Suspensions for intravenous (IV) injection: A review of development,preclinical and clinical aspects☆
Joseph Wong ⁎, Andrew Brugger, Atul Khare, Mahesh Chaubal, Pavlos Papadopoulos,Barrett Rabinow, James Kipp, John Ning
Baxter Pharmaceuticals and Technologies, Global Research and Development, Baxter Healthcare Corporation,25212 West Illinois Route 120, Round Lake, IL, 60073-0490, USA
Received 17 July 2007; accepted 28 November 2007Available online 7 February 2008
f the Advanced Drug Delivery Reviews theme issue on “Clinical Developments in Drug Delivery Nanotechnology”.r. Tel.: +1 847 270 5972; fax: +1 847 270 [email protected] (J. Wong).
With innovations in new target and/or disease specific drugdevelopment, 40% of the new chemical entities coming out ofdrug discovery groups at pharmaceutical companies have beenfaced with poor water solubility challenges, and thereby poorbioavailability [1]. Combinatorial chemistry and high throughputscreening pursued by pharmaceutical companies are intrinsicallybiased towards poorly aqueous soluble drugs [2]. To identify“leads” from such discovery compounds with challenging phar-maceutical properties, various screens are adopted, such as the“Rule of 5” [3]. Identifying the appropriate lead compoundsand further formulating them optimally becomes the key, sincepoor bioavailability is often cited as the reason for the dis-continuation of development of new chemical entities (NCEs).
Poor water solubility of the NCEs is caused by hydro-phobicity, i.e., inability to form hydrogen bonds with water and/or by high lattice energy. One market analysis report estimatedthat worldwide sales of about $37 billion of drugs wereinsoluble or poorly soluble. Insolubility can be defined as morethan 10,000 parts of solvent (water in this case) for one part ofsolute [4] or b0.1 mg/mL. A number of companies saw thisopportunity and attempted to capture an estimated $8 billion inrevenues by reformulating these drugs using novel drug de-livery technologies.
Typically, octanol–water partition coefficient (P) andmelting point (MP) describe hydrophobicity and crystal latticeenergy, respectively. The molar aqueous (water) solubility [5],Su, of an uncharged solute can be calculated using Eq. (1).
log Su ¼ 0:8� log P � 0:01 MP� 25ð Þ: ð1Þ
As can be seen in Eq. (1), the higher the melting point of adrug, the lower is its solubility. If the solute dissolves more inoctanol (non-polar solvent) than in water (polar solvent), the Pvalue would be higher and therefore reflect a lower aqueoussolubility. This log P and MP relationship is an important factorin the selection of an injectable suspension versus an injectableemulsion formulation for a drug [6].
The conversion of an aqueous insoluble drug to a salt form,pH adjustment and the use of cosolvents are typically the initial
steps in the formulation strategy taken to dissolve the drug. Ifthe log P is very high, conventional approaches such as salts,pH or cosolvents may not be sufficient to formulate the drug.For such molecules an emulsion or lipidic system may befeasible, if the melting point is low. Alternatively, inclusioncomplexation may also be explored. The molar ratio ofinclusion complexing agent to drug ratio is generally 1:1 or2:1. The dose of a drug is therefore limited by the allowablehigh molecular weight inclusion complexing agent used in theformulation. The allowable cyclodextrin, for example, used in aformulation is limited by the associated toxicity and highsolution viscosity [5]. If high dose is required, a solid drugnanoparticulate suspension may be selected. Typically the meanparticle size is in the submicron range (b1 μm) and the 99thpercentile particle size is less than 5 μm. The higher the log Pand melting point the higher is the chance for making asuccessful nanoparticle formulation. For example, itraconazolehas been described as a good candidate for submicronsuspension, with a log P and melting point values reported tobe N5 and 166 °C, respectively [7].
In the recent past, it has been found that the majority of thewater insoluble drugs are found in oncology, anti-infective,central nervous system (CNS) and anti-viral therapeuticindications. With the increase in patient population in thesediseases, there has been a strong interest in nanosuspensiondosage forms for injectable applications. Following the recentapproval of a nanoparticulate IV dosage form, Abraxane®(130 nm amorphous particles consisting of paclitaxel entrappedin an albumin matrix), in 2005, there has been a steady increasein the drug nanoparticulate formulations moving into humanclinical trials.
Of all the injectable routes of administration, IV druginfusion/injection provides the most rapid effects. There is lesslimitation on the volume of IV administration and thetherapeutic responses as well as associated toxicity are morepredictable. For other parenteral routes of suspension injectionslike intramuscular (IM), the absorption of drug may take weeksto months [8]. In general, variability in drug absorption for IMinjection is associated depth of injection, lipophilicity of drug,differences in adipose layer thickness and extent of tissueperfusion, including local temperature, edema, etc. The steps in
Fig. 1. Transmission electron micrograph of an itraconazole crystal fromsuspension showing the phospholipid coating (arrows show the multiple bilayerof phospholipids).
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the release of drug from an IM aqueous suspension include(1) diffusion of water, which is affected by blood flow, to theinjection site, (2) dissolution of suspension, and (3) diffusion ofthe dissolved drug to the bloodstream. Dissolution rate is gen-erally the rate-limiting step for drug absorption following IMaqueous suspension administration.
The major potential clinical benefits of a suspension dosageform include (1) high drug loading (because drug is in solidstate) leading to lower volume of injection, (2) reduction intoxicity by replacing solubilizing agents, like Cremophor, withrelatively low quantity of suspension stabilizing surfactants,(3) possibility of altering the pharmacokinetics (PK) of the drugleading to higher dosing and less frequent administration, and(4) possibly passive or even active targeting for drug delivery.Because of these potential benefits, IV injection suspensionformulations have received increased attention [9,6].
This review will primarily address the issues associated withformulation, production and analytical aspects of IV injectablesuspension. Reported preclinical and clinical data will also beincluded to provide an understanding on IV delivery of waterinsoluble drugs formulated as a suspension.
2. Factors to be considered in IV injectable suspensiondevelopment
2.1. Formulation
2.1.1. Excipients for physical stability of suspensionIntravenous administration of solid particles requires the
particle size to be reduced to submicron levels. Once the particlesize is reduced by a selected method suitable for IV admin-istration, the surface area of the suspension particles increasessubstantially. The surface area to volume ratio increases 50-foldby reducing a 10 μm sphere to a 200 nm sphere, for example.In addition, the solubility may also increase as predicted bythe Ostwald–Freundlich equation [10]
lnSso
¼ 2Mg
qRT1r� 1ro
� �ð2Þ
where r is particle radius, ρ is density, γ is interfacial tension,T is temperature,M is molecular weight, R is gas constant, S andSo are the solubility of particles with radii r and ro respectively.For a flat starting particle (ro approaches infinity) the increase insolubility ratio, S/So, has been calculated to be larger than 2, asthe particle size is reduced below 200 nm [1]. Both the increasein surface area and solubility of nanoparticles contribute to theincrease in dissolution rate as predicted by the Noyes–Whitneyequation [10].
The increase in contact surface area also causes particles toagglomerate. Surface-active compounds (surfactants) can beused to stabilize the suspension particles, at surfactant:drugratios as low as 1:10 [9]. There are only a limited numbers ofnonionic and anionic surfactants that have been approved asexcipients for parenteral use, including phospholipids, poly-sorbate 80, and poloxamers. There may be safety concernsregarding the use of cationic surfactants. The cell membrane
readily absorbs cationic surfactants leading to hemolysis [11].However, the addition of phosphatidylcholine has been reportedto reduce the toxicity of cationic and anionic surfactants [12]. Toqualify a surface-active agent as a suspension dispersant [13],the following criteria are desired [14]:
1. Ability to adsorb on the hydrophobic surface of suspensionparticles in the manufacturing process.
2. Inability to adhere to the surfactant coating of adjacentparticles.
3. Ability to provide repulsion between dispersant-coatedparticles due to steric hindrance and/or electrostaticrepulsion.
An example of a commonly used nonionic surfactantis poloxamer [15] that is a block copolymer of lipophilicpolyoxypropylene and hydrophilic polyoxyethylene, HO[CH2CH2O]x–[CH(CH3)CH2O]y–[CH2CH2O]zH. Phospholi-pids are also commonly used neutral or charged stabilizers. Atransmission electron microscopy image of a multiple bilayerphospholipid coating on an itraconazole suspension particleis shown in Fig. 1. Combinations of anionic and nonionic sur-factants in stabilization of suspensions and studies of dispersantcoatings have been published. Stabilization of nanospheresuspensions following lyophilization may be achieved byreplacing poloxamer (which crystallizes during freezing) withsodium deoxycholate [16]. Long circulating particles that canavoid capture by the reticuloendothelial system (RES) may beprepared by coating the particle surface with phospholipid–polyethylene glycol (PEG) leading to an increase in the bloodcirculation half-life of the particles by several orders ofmagnitude. The phospholipid–PEG provides a hydrophilicprotective layer around the nanoparticles. The resulting stericrepulsion repels the adsorption of opsonin proteins and thereforeblocks and delays the first step in the opsonization process [17].
Table 1Human blood vessels
Blood vessels Lumendiameter
Average wallthickness
Estimated total cross-sectional area
Aorta 2.5 cm 2 mm 4.5 cm2
Distributing artery 0.4 cm 1 mm 20 cm2
Arteriole 30 μm 20 μm 400 cm2
Capillary a 6 μm 1 μm 4500 cm2
Venule 20 μm 2 μm 4000 cm2
Vein 0.5 cm 0.5 mm 40 cm2
Vena cava 3 cm 1.5 mm 18 cm2
a Depending on the functional state of the tissue, capillaries can increase ordecrease the diameters beyond the 6 to 8 μm diameter range.
Table 2USP extraneous particle counts in injections
≥10 μm ≥25 μm
Light obscuration methodSVP 6000 600 per containerLVP 25 per mL 3 per mL
Microscopic methodSVP 3000 300 per containerLVP 12 per mL 2 per mL
SVP: Small volume injection applies to drug packaged in container with volume≤100 mL.LVP: Large volume injection applies to drug packaged in container with volumeN100 mL.
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For particles that are not PEG coated, the adsorbed opsoninproteins interact with plasma membrane receptors on monocytesand certain tissue macrophages leading to recognition of theparticles by these cells [18].
2.1.2. Roles of excipients in suspension instability and toxicityThe tendency of smaller particles in a suspension to dissolve
and re-grow on bigger particles presents a mode of instability,termed Ostwald ripening.
Ostwald ripening happens because of the Kelvin effect,especially for particles in the size range of 0.1 to 0.5 μm andbelow [19]. In general, the speed of Ostwald ripening may becontrolled by molecular diffusion or surface reaction [20]. IfOstwald ripening proceeds under diffusion-controlled growthkinetics, then faster ripening can be expected if smaller particlesexist in the suspension and the solubility of the large particles ishigh. Ostwald ripening could be minimized if the particledistribution is narrow [21].
If Ostwald ripening proceeds under very low supersatura-tion, then interfacial reaction is likely to be the cause. Additionof carboxymethyl cellulose to the formulation may preventreaction-controlled ripening. However, it has been reported thattoo much dispersant used in the stabilization of a suspensioncould actually promote Ostwald ripening. The proposed weightratio of drug to stabilizer (dispersant) was advocated to be in therange of 20:1 to 2:1 [22]. It is recognized that only excipientswith established safety profiles should be used in stabilization ofsuspensions. It has been reported that the surfactant and not thesize of the nanoparticles impacts the viability and cytokineproduction by macrophages as well as cyototoxicity followingIV injection [23,24]. As always, safety is related to the quantityof the dispersant used and sometimes its purity [25]. Poloxamer,for example, covers a family of these macromolecular sur-factants. Commercial poloxamer 407 has an average molecularweight of 12,000 (with a range between 9000 and 16,000).Animal studies in irritation, acute toxicology, immunotoxicity,repeated dose toxicology, genetic toxicity, chronic carcinogeni-city and reproductive toxicity were performed. Althoughpoloxamer 407 has been regarded as non-toxic, its ability tocause hypertriglyceridemia and hypercholesterolemia in ratsraises concerns. The alteration of lipidic profile and reportedrenal toxicity pose a potential barrier for use in parenteralformulations [26]. Pluronic F108, on the other hand, has been
used in the formulation of IV injectable itraconazole and aclinical trial of the suspension (50%b200 nm and 90%b335 nm) has been conducted [27].
In addition to the selection of surfactant for physical stabilityof the suspension, the basic requirements for IV injectableformulation include the use of tonicity adjusting agent andbuffer. It is important to note that if an ionic surfactant is used,selection of the buffer and its associated quantity need to beevaluated to avoid neutralization of charges leading todestabilization of the suspension.
2.2. Intravenous introduction of particles
2.2.1. Distribution of radiolabeled spheres following IVinjections in dogs
In one study, radiolabeled 25 μm, 15 μm, 8 μm and 3 μmspheres were injected into beagle dogs [28]. The≥8 μm sphereswere found localized in the lungs. The 3 μm spheres wereinitially found in the lungs and were then recovered in the liver(75%) spleen (17%) and other organs. Three percent were stilllocated in the lungs and the rest of the spheres were in thekidneys and heart. No differences in the distribution wereobserved when the dose was administered using IV bolusinjection or 30 min infusion.
2.2.2. Sources of particle introduction—IV drug therapy,musculoskeletal trauma, cardiopulmonary bypass surgery,vertebroplasty, IV drug abuse, etc.
As can be seen in Table 1, the suspension, following an IVinjection into the vein will encounter the venules (lumendiameter of about 20 μm) and capillaries (lumen diameter ofabout 6 μm) in the lungs. The limit for extraneous particlesallowed by the United States Pharmacopeia (USP), Chapter788, is shown in Table 2 [29]. It is important to note that theparticle size limits in USP chapter 788 are not designed fordispersions of IV injections. Rather, they are intended asguidelines for environmental/extraneous particle contaminationin IV injections.
In terms of intravenous foreign body introduction, it has beendocumented in the published literature that particulate matter inintravenous fluids such as rubber stopper fragments, glass,synthetic polymers, fibers, starch, and precipitated calcium–
Fig. 2. Field emission scanning electron micrograph of a filtered aliquot of anitraconazole suspension.
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phosphate crystals in total parenteral nutrition infusion can alsobe introduced into the body. Particles are introduced quite ofteninto the blood stream via IV drug therapy [30], musculoskeletaltrauma [31], cardiopulmonary bypass surgery [32], etc.Significant numbers of patients with fractured long bone orsevere musculoskeletal trauma had fat droplets in thepulmonary capillaries. Complications related to vertebroplasty,the injection of bone cement (e.g., polymethyl metacrylate) intothe fractured vertebrae for the fast relief of pain, may alsointroduce particles into the body [33]. The risk of venousembolism has been well documented in chronic IV drug addicts[34,35]. Typically, a combination of foreign particle embolismand inflammatory responses is observed in long-term follow-upevaluations of drug abusers [36,37]. For example, IVmethadone abusers would crush thousands of tablets over theperiod of years, dissolve the content in water and inject in-travenously. Subsequently, granulomatous mass lesions in thelungs due to talcosis were observed. There is 5% talc in each10 mg tablet [38].
2.2.3. Microparticulate induced phlebitis and injection rateIt has been reported that drug precipitate formed during the
injection of IV solution may cause phlebitis [39], an inflamma-tion of a vein, or even pulmonary embolism [40]. It is unclearthat the injection of suspension would cause phlebitis. However,drug precipitation, and therefore the microparticulate inducedphlebitis, associated with injection of IV solution may beavoided by employing a slow injection [41]. A slow injection ordeep vein injection, allows the formulation to be rapidly dilutedby blood and therefore minimizes the particulate numbers.
In a beagle dog study, acute hypotensive effect was reportedwith a peak at 2.5 min following IV injection of a 5% (w/v)suspension (200 nm polystyrene spheres coated with PluronicF108) at 1 mL/min [42]. However, no effect was observed withthe injection of 50 nm suspension particles. The dose ofsuspension was 0.1 mL/kg of body weight. Full recovery wasobserved after 60 min. While severe sinus bradycardia wasdetected at the peak, no other primary electrocardiographicabnormalities were noted. Reducing the particle load and rate to1% suspension (200 nm) at 0.5 mL/min also could eliminate theacute hypotensive effect.
During the pharmacokinetic evaluation of IV itraconazolesuspension in human subjects (single dose of 300 mg), it wasfound that an infusion rate of 300 mg/h caused acute severelocalized back pain, accompanied with lumbar muscular spasmsin 2 of the healthy human subjects [27]. The infusion wasdiscontinued. When the same dose was infused at 100 mg/h, norelevant side effects were observed. The particle size distribu-tion of the itraconazole suspension was reported to be 50%b200 nm and 90%b335 nm. The suspension was milled andstabilized using Pluronic F108.
2.2.4. Dispersion for IV administration
2.2.4.1. Particle size. Assuming that a dispersion, such asemulsion, liposome, suspension, etc., for IV administration isphysically stable, the particle size distribution, particle
morphology, as well as components of the formulation are themajor parameters characterizing the dispersion formulation andthe associated safety in administration. Particle size measure-ment becomes a critical activity especially for IV injections,since particle size determines safety and distribution of theparticles in vivo, and stability of the particles during storage.Particle size measurement methods depend significantly on thetype of instrument used, as well as the input parameters used bythe instrument in its calculations. Some of these considerationsare discussed below. Since a number of these factors have beenwell studied for parenteral emulsions, analogies and learningsfrom emulsion literature have also been discussed.
2.2.4.2. Particle size measurement methods. Particles in apopulation may be analyzed discretely (particle countingmethods: e.g., microscopy, light extinction counter, etc.) orcollectively (e.g., light scattering, photo correlation spectro-meter, etc.) [43,44]. Measurement of the particle size distribu-tion of a dispersion is not necessarily a straightforward task.Issues with sampling and particle overlap often complicateoptical measurement techniques. The complexity of thisapproach is illustrated in Fig. 2, which shows the scanningelectron micrograph (SEM) of an itraconazole suspensionsample after filtration. Alternatively, instrumental particle-sizing methods using a collective approach, rather than opticalmethods, appear to be a practical option in the determination ofthe suspension particle size distribution. Even instrumentalparticle-sizing methods using a discrete approach may not besuitable, as excessive sample dilution in a dispersion formula-tion, especially in the case of suspension, can cause dissolutionof suspension crystals. Light extinction sensors can count up toabout 40,000 particles at a flow rate of 5 mL/min [43]. Laserlight scattering techniques (collective method) also require acertain level of sample dilution so as to allow light transmissionin the range specified by the equipment manufacturer. A staticlaser light scattering technique [45] for example, has thecapability to measure particle size in the range of 0.02 to2000 μm. The particle size can be reported as volume or massweighted, number weighted or surface area weighted. For a
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dispersion sample with relatively small number of substantiallylarge particles, number-weighted results are inevitably biasedtowards reporting smaller mean particle size value. As such, themost common particle size method reported in the literature, byfar, is volume-weighted [46]. Nevertheless, the effect of dilutionon particle size measurement by any method should beevaluated during the method development process.
Particle size, shape and number are important parameters inpopulation analysis. There is no one particle-sizing method thatis superior to all the rest. All techniques have limitations interms of accuracy, precision, particle size range, speed ofparticle size distribution determination, ease of use, sample sizeand preparation, sensitivity, etc. The strengths and weaknessesof various available particle-sizing methods for the pharmaceu-tical industry have been discussed extensively [47].
In addition, the size of non-spherical particles is oftenreported as diameter of an equivalent volume sphere. Char-acterization of the irregular particle shape has been described inliterature [48]. The particle shape issue is particularly relevant tothe dispersion sample that happens to be a suspension. Theapproach of mathematically converting suspension particleswith non-spherical geometry to equivalent volume sphereshelps to reduce the effect of particle shape in size determinationas long as the number of particles is large enough and in randomorientations during measurement. Due to the complexities incomputation, the version of software used for a particularparticle-sizing instrument must be disclosed to assess thepotential error introduced. In addition, different numericalalgorithms used by different manufacturers could calculatedifferent particle size distribution results for the same suspen-sion sample [49].
The use of light scattering technique in particle sizedetermination also requires the identification of real refractiveindex of the particles measured [50,51]. Because the liquid flowin the measurement cell of a particle size analyzer is turbulent,the particles in dispersion will be in random orientations. For acrystal sample with a range of reported real refractive indices[45] the use of the average real refractive index is recom-mended, which is the same approach as if a measurement of amixture of different materials with different refractive indices isperformed [51]. Impact of the imaginary component of therefractive index should also be assessed [44]. Technically, theMie theory in laser scattering analysis applies to sphericalparticles of less than 1 μm in diameter. In the case of an IVinjectable dispersion, the Mie theory has been applied indispersion size measurements. As discussed before, therefractive indices of the suspending particles as well asmeasurement medium such as water are required, as a certainlevel of dilution needs to be performed in the measurement cellof the equipment. However, laser diffraction is reported to beinsensitive to the presence of large particles between 1 and 3%by volume [47] and lipid emulsion with globules larger than5 μm did not provide a linear response. Rather a light obscu-ration technique was recommended for emulsions [52].
The dynamic light scattering (DSL) technique that utilizesthe principle of Brownian motion can measure particles in therange of 0.6 nm to 6 μm [53]. DSL is also known as photon
correlation spectroscopy (PCS) or quasi-elastic light scattering(QELS). The DSL technique reports particle size as hydro-dynamic radius. Hydrodynamic radius is defined as the radius ofa hard sphere that diffuses at the same rate as the particle underexamination. The reported hydrodynamic size (Z average) isweighted by the particle scattering intensity. The factors that canaffect the reported hydrodynamic radius include shape, density,properties of suspending fluid (e.g., refractive index) andtemperature. No dilution of the dispersion is required in themeasurement process. A published paper has reported that staticand dynamic scattering techniques could make aggregatesappear to be smaller due to intra-aggregate interference [54],especially when the aggregate size is about the same magnitudeas the wavelength of the measurement light beam. This effect isdue to the reduction in scattering intensity in static lightscattering method or in frictional resistance in dynamic lightscattering measurement.
The use of ultracentrifugation [55] in particle size distribu-tion has also been published and claimed to be a far moreprecise method with better resolving power. All in all, eachmethod has its own unique set of technical issues that has to beresolved and each method may only be suitable for a specificapplication. Regardless of which method is selected, analyticalmethod validation [56] is required for regulatory submission.
2.2.4.3. Upper dispersion size limit for emulsion. In 1980 theBritish Pharmacopoeia specified that the diameter of fatglobules in emulsion should not exceed 5 μm [57]. Thisrequirement, however, is not in the current British Pharmaco-poeia. A series of publications stated that irrespective ofemulsion lipid concentration, the volume-weighted percent ofN5 μm (i.e., volume-weighted percentage of fat greater than5 μm (PFAT5)) should not exceed 0.05% [58,59]. The USPPharmacopeial Forum [60] has published this requirement andthe associated measurement methods [61]. Per the Forum,dynamic light scattering (DLS), also known as photoncorrelation spectroscopy (PCS), or static light scattering (SLS)based on Mie theory may be used for the determination of meanglobule diameter and the standard deviation. Per the Forum, theproposed intensity-weighted mean droplet diameter measuredusing DLS technique must be less than 500 nm, irrespective ofthe lipid concentration. Incidentally, if SLS is used, the sampleconcentration in the measurement is recommended to becontrolled at blue-light intensity of above 70%, preferably atabout 80%, in order to avoid underestimation of emulsionglobule diameter due to multiple scattering [62]. For character-izing globules larger than 5 μm, the single particle opticalsensing (SPOS) technique, based on light obscuration or lightextinction particle counting methods are proposed. The USPPharmacopeial Forum has proposed the requirements [60]:
The volume-weighted, large-diameter fat globule limits ofthe dispersed phase, expressed as the percentage of fatresiding in the globules larger than 5 μm (PFAT5) for agiven lipid injectable emulsion, must be less then 0.05%.
The arguments for these recommendations center onemulsion stability and safety. In terms of emulsion stability,
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the supporters of these recommendations have indicated thatelevated PFAT5 values are associated with coalescence or phaseseparation leading to free oil formation [63]. Pathophysiologicchanges in vital organs in animals were also reported for lipidinjectable emulsion PFAT5 higher than 0.05% [64]. Based on anumber of animal studies, infusion of unstable emulsion waslinked to oxidative stress in the liver, in addition to potentialpulmonary embolism [58].
Of course there are counter arguments to dispute theassertions of the 5 μm limit with respect to emulsion stabilityand safety. In terms of safety, a paper [57] has been published in1996 concluding that the limitations on particle size in fatemulsion should be reconsidered. The 1980 British Pharmaco-poeia monograph [65] was the only official particle size limit forinjectable emulsions ever mentioned:
Intravenous infusions are sterile aqueous solutions oremulsions with water as the continuous phase; they arefree from pyrogens and, as far as possible, made isotonicwith blood. They do not contain added antimicrobialpreservatives or buffering agents. The diameter of globulesof the dispersed phase of emulsions does not exceed 5 μm.
As mentioned above, this 5 μm requirement is not in thecurrent British Pharmacopoeia. According to this investigationpublished in 1996, a significant number of lipid emulsionglobules with diameter larger than 5 μm were detected incommercial parenteral fat emulsion products. The lightobscuration technique was used to determine particles largerthan 5 μm. These products have been used in humans for yearswithout reports of important adverse reactions. Lipid emulsionglobules with diameter even larger than 7.5 μm may passpulmonary vasculature by deformation [66]. Even occlusion ofpulmonary capillaries by lipid emulsion globules larger than5 μm may be reversible following biodegradation [67].
In terms of stability, recent work has clearly demonstratedthat it is the time-dependent behavior of globule sizedistributions that is predictive of phase separation instability.A single-point measurement of PFAT5 is insufficient to reliablypredict emulsion stability due to the disparity in initial PFAT5
levels for commercial emulsions. Time-dependent changes inPFAT10 were found to be more predictive of phase separationinstability [68]. PFAT10 is the percentage of fat residing in theglobules larger then 10 μm. Nevertheless, the USP appears to bemoving in the direction of accepting the recommendationsstated in the Pharmacopeial Forum [60].
2.2.4.4. Implication of the proposed upper dispersion size limitfor emulsion on IV suspension. Physically, lipid emulsionglobules have been regarded as deformable. As such, there is aperception that rigid solid particles could present a much lowerLD50 when compared with fat globule [59]. By inference, thereis a temptation to apply the proposed requirements (i.e.,volume-weighted percent of N5 μm to be less than 0.05% andthe mean globule diameter b500 nm) in the USP PharmacopeialForum [60] for nutritional fat emulsion to IV injectablesuspensions. There are considerable obstacles to applyingthese limitations to nanosuspensions possessing unique proper-
ties including compositions, morphologies, and particle sizedistributions relative to lipid emulsions. It is the clinical safetydata relevant to nanosuspensions that should drive proposedsafety limits. Furthermore, physicochemical stability considera-tions should be based on techniques predictive of time-dependent responses to ensure that the clinically establishedsafety limitations are not encroached during the period ofintended use. Finally, use of SPOS-based methodology forspherical emulsions may not be uniformly suitable for the non-spherical particles (see Fig. 2) contained in many nanosuspen-sions. Therefore, application of the acceptance criteria to solidsuspensions using the USP Pharmacopeial Forum proposal fornutritional fat emulsion appears inappropriate at this time.
2.3. Scale up and manufacturing
There are numerous methods of producing suspensions forinjection [1], including but not limited to homogenization,media milling, precipitation and combinations of these.However, challenges still reside in the production of a sterileand pyrogen-free suspension, which is after all a heterogenoussystem for intravenous administration.
2.3.1. Dosing uniformityUSP content uniformity requirements apply to suspensions in
single-unit containers [69]. Variation of particle size due topotential agglomeration, aggregation or wide span of crystal size/shape could possibility lead to weight variation. Therefore,physical stability of the IVinjectable suspensionmust be achievedfor the intended shelf life of the product. Insufficient mixing of asuspension may also contribute to variability, as dispersions maybe viscous. Sedimentation during production and prior to vialfilling may also be a concern. The content uniformity at theproduction level needs to be validated for product release.However, training of hospital staff also must to be considered forproper uniform mixing of the suspension prior to IV administra-tion. For example, package insert of Abelcet® discloses thepreparation of admixture for infusion. It requires shaking of thevial gently until there is no evidence of any yellow sediment at thebottom. The 5-micron filter needle supplied with each vial is thenattached to the syringe before injecting the suspension into an IVbag containing 5% Dextrose Injection USP.
2.3.2. Polymorph and crystallinityIf sterile drug of the thermodynamically stable polymorph is
available, direct homogenization for surfactant coating andreduction of particle size may be performed to asepticallyproduce an IV injectable suspension with mean volume-weighted particle size of less then 1 μm. If sterile drug is notavailable, then the drug may be dissolved in an organic solventand filtered via a 0.2 μm filter. A sterile antisolvent may then beused to precipitate the drug for aseptic production of thesuspension. However, crystals formed by precipitation maycontain inclusions — pockets of entrapped impurities such assolvent. Crystals with solvent inclusions may show differentphysical properties. It was also known that different crystal-lization conditions could produce different polymorph. For
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example, polymorphs I and II showing different X-ray dif-fraction profiles of itraconazole were produced in the develop-ment of a potential suspension dosage form [45].
In other cases, amorphous solids could be obtained viaprecipitation. However, disordered nanocrystalline materialmay also exhibit an “X-ray amorphous” pattern due to theabsence of its long-range order. True amorphous material, ascited by the publication, is defined by the absence oftranslational, orientational, and conformational order of indivi-dual molecules [70]. The short-range order of a few moleculardimension is typically exhibited by amorphous solids. It isimportant to note that X-ray diffraction pattern can detectmolecular order. Disorder, however, is only implied [71].
Slow crystallization often leads to formation of the morestable polymorph. However, it could also form larger crystals[72]. In order to avoid the use of a milling process, which couldreduce the yield by 2–5%, ultrasound and temperature cyclingwas employed to produce uniform small crystals. The mixing,nucleation and growth rate of the crystallization process has alsobeen investigated to control particle size [73]. It is generallyrecognized that the smaller the starting crystal size the easier it isto reduce the product particle size by milling or piston gaphomogenization. In addition, homogenization may be applied tofacilitate the coating of particles with surfactants that areessential in conferring physical stability to the suspension.
Depending on the pharmacokinetics and pharmacodynamicrequirements, amorphous or crystalline IV injectable suspen-sions may be developed. The suspension with amorphous solidparticles could be stabilized by lyophilization. Crystallineparticles in IV injectable suspension may provide an IV depotcontrolled release of drug [1]. On the other hand, microparticlepiroxicam, dantrolene and flurbiprofen have been reported toachieve rapid dissolution upon injection in animals [9].Furthermore, organ distributions of microparticulate flurbipro-fen in animals following IV injection were shown to be identicalto the one resulted from unformulated drug [74].
2.3.3. MixingAdequate mixing of a suspension presents a unique set of
challenges. Blending time could affect surfactant coating aswell as uniformity of the distribution of the suspended particlesin the feeding vessel prior to homogenization. For a smallcontainer, the tank surface area to volume ratio is much largerthan a production-scale mixing tank. Also, the addition time forthe excipient solution and drug (e.g., dissolved in organicsolvent) is much higher than for the small-scale case. Theselection of impeller has been studied [75] for suspensions,which could experience sedimentation during production or invial filling operations. Typically there are two types ofimpellers. The propeller and fan turbine are the axial flowimpellers, whereas flat blade turbines and paddles result inradial flow during mixing. The mixing tank can also be baffledto allow top-to-bottom flow and therefore real mixing. Under-standably, precautions must be taken to avoid trapping andaccumulation of drug particles at the baffles. Typically, eachbaffle should be about 1/12 the diameter of the tank, T. Theoptimal static liquid depth, Z, to tank diameter ratio (or Z/T) is
between 1 and 1.2. The minimum static liquid depth should notbe less than 1/3 of the tank diameter. If the static liquid depth totank diameter ratio is larger than 1.2, then multiple impellers areusually required. The impeller diameter, D, is typically 1/3 thediameter of the tank (T). The axial flow impeller should beplaced between 2/3 and 1 impeller diameter (D) off the tankbottom. In suspension mixing, the flat-bottom tank equippedwith a small fillet may also beneficial [76].
One problem of vortexing is air entrainment, especiallyfoaming resulting from the surface-active compounds used tostabilize the suspension [77]. Foamability of ionizable amphi-philic compounds varies as a function of pH. Unionized andionized amphiphilic species have different foaming properties.Instead of centering the shaft in a regular tank (i.e., no baffles)that could cause vortexing, the propeller may be set at anangular off-center position to allow a top-to-bottom patternessentially equivalent to that in the baffled tank [75].
Because suspension particles settle, constant mixing isrequired to allow uniform mixture throughout the entire tank.As reported in the literature, if the settling velocity is less than1 ft/min, no concentration gradient of suspension is expected aslong as a low power mixing using a propeller impeller is applied[75]. Turbine impeller is reserved for more difficult applications.
Regardless of which impeller, tank and power are selectedfor nanosuspension mixing, a turbulent flow is required to allowrapid eddy motion leading to efficient mixing [78]. As such, ahigh Reynolds number, NRe, of larger than 104 is preferred formixing in a baffled tank. NRe is defined as
NRe ¼ D2xqLg
ð3Þ
where D is the impeller diameter, ω is impeller rotational speed(revolution/s), ρL is liquid density, and η is the liquid viscosity[79]. Axial flow, rather than radial flow, impellers are preferredbecause they are more efficient pumping devices allowing betterflow of the suspension. As theoretical prediction is not feasible,empirical correlations for NRe and power number (powerrequirement, P, in J/s), Np, for a given system (see Eq. (4))must be obtained experimentally.
NP ¼ PD5x3qL
ð4Þ
The scale up for suspension mixing has also been discussed[80,76,78]. The relationship between impeller speed to justcause suspension of particles in the medium, NJS, and thedimensionless number, S, is shown in Eq. (5).
NJS ¼ 1D0:85
Sv0:1 d0:2p gDqqL
� �0:45
X 0:13
" #ð5Þ
X ¼ WS
WL100 ð6Þ
where D is the impeller diameter, ν is kinetic viscosity, dp isparticle size, g is gravitational constant,Δρ is density differencebetween the particle and fluid, ρL is fluid density, WS is the
947J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
weight of solid and WL is the weight of liquid. S is dependenton geometry of the impeller (type), impeller distance from thetank bottom, and the impeller to tank sizes ratio. With thegeometry of (1) flat-bottom tank, (2) static liquid depth to tankdiameter ratio of 1 (i.e., Z=T), (3) impeller diameter to tankdiameter ratio of 1/3 (i.e., D/T=1/3), and (4) impeller clearanceabove bottom, C, to tank diameter ratio of 1/4 (i.e., C/T=1/4),the S value was determined to be 7.9 [79].
2.3.4. SyringeabilitySyringeability is an important factor to consider for
intravenous delivery. This is the pressure association with theinjection via a needle of predetermined gauge and length. Anexample of a syringeability test apparatus has been proposed[81]. For injection of a nonaqueous formulation, the forceapplied to the syringe plunger attached to a needle is dissipatedin the frictional resistance of the traveling plunger, the motion ofthe liquid in the barrel and the resistance of the liquid throughthe needle. For nonaqueous suspension, the syringeability wasfound to be proportional to the 4th power of the diameter of theneedle (d) and inversely proportional to the length of the needle(ln) and viscosity (μ). The equation for syringeability is shownas follows:
Syringeability ¼ kd4
128Alnð7Þ
For IV injection of an aqueous suspension, simulation ofsyringeability can provide a reliable and reproducible qualitycontrol test for the product.
2.3.5. Sterility and pyrogenicity
2.3.5.1. Sterility. One of the important safety requirements foran IV injectable suspension is sterility assurance [82]. It hasbeen recognized that crystallization could entrap bacterialspores [83] and these isolated entrapped spores can be resistantto formaldehyde and ethylene oxide [84]. In fact, studies haveshown that entrapped spores may be stable and extremelyresistant to destruction by moist and dry heat [85,86].
Terminal sterilization of the final product at 121 °C for anextended period of time and then cooling down to roomtemperature could cause physical or chemical instability — theincrease and decrease in solubility of the suspension drugparticles, a scenario for Ostwald ripening. For a proposedparenteral suspension for veterinary administration (oxytetracy-cline), the use of gamma radiation has been demonstrated to beeffective in sterilizing the product [87]. This oxytetracyclinesuspension was also physically stable for at least one year.However, general acceptance of gamma irradiation by thepharmaceutical industry for IV injectable suspension for humanuse is unlikely due the potential formation of free radicals byionizing radiation. However, if the suspension can belyophilized, this elimination of water can sufficiently improvethe stability of the final product by gamma radiation [88]. If theparticle size of an IV injectable suspension is small enough,sterile filtration is possible. An example is the NanoCrystal™,
X-ray contrast agent iodipamide [89]. The mean particle sizewas reported to be 98 nm with all particles less than 220 nm.100% of Pseudomonas diminuta (≥107 organisms/cm2 ofeffective filtration area) were retained by the 0.2 μm Supor®200 DCF™ filter (Gelman Sciences. Ann Arbor, MI).
Aseptic manufacturing of the IV injectable suspension is alsoa practical option. There are two ways to manufacture IVinjectable suspensions using aseptic techniques. One way is tosterilize the excipient solution containing surfactants andinsoluble raw drug material separately. If the excipient solutionis not stable to heat it may be filtered via 0.2 μm and/or 0.1 μmfilters. The raw drug material can be sterilized by gammaradiation [88] or by dry heat [90] if the raw material is stable toeither method applied. The suspension can then be manufac-tured aseptically by combining the two and then processingfurther. However, dry heat of drug powder at 145 °C for 3 h maycause sintering which is characterized by three stages —smoothing, sticking and shrinking, leading to reduction of thepowder surface area and hardening. The powder surfaceroughness is first smoothed out followed by adhesion andwelding of the particles. This process causes the space and poresin between and within particles to disappear. The secondmethod involves the filtration of all components in liquid formbefore processing. The raw drug material can first be dissolvedin a suitable organic solvent and filtered via a compatible0.2 μm and/or 0.1 μm filters.
The risk factors associated with aseptic manufacturing ofsterile products have been discussed by the Food and DrugAdministration [91]. The risk factors associated with sterilityassurance include personnel, facility and room, aseptic processline, process, HVAC (heating, ventilation and air conditioning),deviation and environmental control trends, disinfectionspractices, quality assurance and control, and media fills.
Per the USP [92], 2% or 20 containers, whichever is less, aresampled for testing for a batch of more than 500 containers.Passing the tests do not necessarily ensure a batch of product issterile or has been sterilized. Per the USP, validation of theaseptic processing procedures is required to ensure that theproduct is sterile. As an example, the sterility assurance ofinjectable microspheres of leuprorelin has been published [93].Since gamma radiation degrades polylactic/glycolic acid(PLGA) and leuprorelin and the PLGA glass-transitiontemperature is low for heat sterilization, a week-long asepticproduction was developed. The current pharmacopeial methodonly requires the test of sterility in the aqueous medium and onthe exterior of the microspheres and does not indicate thesterility on the interior of the microspheres. This samepharmacopeial requirement also applies to IV injectablesuspensions. Direct inoculation rather than the membranefiltration (0.45 μm) therefore may be more suitable to be usedin this sterility testing. As discussed earlier, the assurance ofsterility can only be accomplished by validation of the processand not simply by testing of a limited number of samples. In thecase of leuprorelin microspheres, the scientists developed amethod that could test the sterility in the interior of themicrospheres as well. A solvent was found that could dissolvethe microspheres and was miscible with culture media without
948 J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
exhibiting inhibitory effects of the bacterial spores. The sporesinclude the ones found in the bioburden assessment ofmanufacturing facility as well as the compendial test organisms.All waste solution/solvent in the manufacturing process wastested for sterility.
2.3.5.2. Endotoxins. USP Chapter 85, Bacterial EndotoxinsTest [94] has requirements for bacterial endotoxin level inexcipients and in the final product. Nanogram quantities oflipopolysaccharides are sufficient to cause an IV injectablesuspension to be pyrogenic. Depending on the intended dose ofactive drug and the suspension formulation, the limits onendotoxins for the final product can be determined using theequation K /M, where K is the threshold human pyrogenicdose of endotoxin per kg of body weight (i.e., 5 EU/kg) andM is the maximum recommended human dose per kg of bodyweight in a single hour period. The body weight is assigned tobe 70 kg. For example, if the final product contains 0.05 g/mLof an active drug and M is 3.5 g/h, then the endotoxin limitfor the final product is 5 EU/mL. Again, the current pharma-copeial method will only require the test of endotoxins in theaqueous medium and on the exterior of the suspension particles.Validation of the manufacturing process is the key to ensure thatthe product endotoxin limit is not exceeded. Current pharma-copeial methods include the gel-clot techniques and thephotometric techniques (turbidimetric and chromogenic tests)using Limulus Amebocyte Lysate (LAL) reagents.
2.3.5.3. IV injectable suspension pyrogenicity. An alternativeto the endotoxin test is the USP pyrogen test [95]. Prior toproduction, individual excipients typically must first meet USPlimits on endotoxin. Pieces of glassware are then depyrogenatedat 250 °C with dry heat for not less than 30 min. The equipmentsurfaces, including rubber, plastic and metal, etc. are cleanedusing a validated method. If necessary, a pharmaceutical bio-degradable detergent such as Pyroclean™ (ALerCHEK, Inc.,Portland, ME), which solubilizes endotoxins for removal viawater flushing may also be used. Following the injection of thesuspension intravenously into three rabbits, if none the animalsshow an individual temperature rise of 0.5 °C or more above itsrespective control temperature for 3 h, the suspension passes thetest. If not a retest procedure needs to be followed. This testcould be used for product release.
3. Preclinical and clinical information
3.1. Safety
3.1.1. Approved, safe nanoparticulate dosage formsA number of studies have been conducted to demonstrate the
safety of injecting nanoparticles into the blood stream. Humansafety data have been published for albumin-bound paclitaxelnanoparticles (mean particle size 130 nm) [96]. The studyindicated that no significant adverse events were attributable tonanoparticles when administered at 10 or 30 mg/m2. Moderateneutropenia, moderate sensory neuropathy, and mild tomoderate, reversible alopecia occurred at doses of 70 and
100 mg/m2. In another clinical study, highly porous particlescontaining paclitaxel were infused intravenously into 22 cancerpatients [97]. Although this reference did not describe theparticles, another publication indicated that the porous particleswere prepared by spray drying and when reconstituted inaqueous system, had a mean size of approximately 2 μm [98].
3.1.2. Requirements for a safe injectable nanosuspensionThe safety of intravenously injected particulates will be
considered from two perspectives: 1) potential vascularocclusion and 2) potential compromise of the monocytephagocytic system or MPS.
3.1.2.1. Potential vascular occlusion: in vivo distribution as afunction of particle size. The time course of the biodistribu-tion of intravenously injected particulates is dependent uponparticle size. Particles larger than 7 μm are sequestered by thefirst large capillary filtration system they encounter, the pul-monary vasculature. In the lung, alveolar macrophages carryparticles less than 12 μm in size [99] through the capillary walls,permitting excretion into the sputum and subsequently out ofthe lung. Provided that the particle load is kept sufficiently low[43], the extensive collateral circulation of the pulmonaryvasculature mitigates potential particulate blockage of capil-laries, with anticipated reduction of blood flow. Certainly,blockage can occur if the particulates are sufficiently large.Thus, capillary occlusion appeared to occur in the lungs ofrecipients of transfused unfiltered blood, which can containparticles of 20 μm to 500 μm in size. This effect was found to beeliminated by employing Dacron® wool depth filters of 40 μmto 80 μm size cutoff. This suggests both an approach to controlhigh particulate burdens of excessively large-sized nanosuspen-sions, as well as the acceptability of particles less than 40 μmfrom such products [43].
If they remain intact and are not dissolved, particles smallerthan 7 μm migrate from their initial lung entrapment ratherquickly [100], within minutes, but are phagocytized by the nextmajor filtration system they encounter, the fixed macrophagecells of the liver and spleen [101,102]. Phagocytosis or particleingestion is a normal function of these cells, when presentedwith microbes, or foreign particulates of size less than about8 μm. In several rat studies, no evidence of an inflammatoryreaction was found with ingestion of inert particulates.Histologically, a low incidence of focal myocardial degenera-tion was found with 10 μm and 40 μm particles. Apparently safelevels of 8×106 particles/kg of size 0.4 μm to 10 μm or 4×105
particles/kg of particles of size 40 μm could be administered.These safe levels in animal studies may be compared with
those for approved particulate products for man. OPTISON™(Perflutren Protein-Type A Microspheres for Injection, USP),Amersham Health Inc., is an approved albumin microspheresuspension for echocardiographic imaging. Ultrasound-induceddisruption of the primary particles results in a short residencetime in the body. However, a secondary burden of smallerparticles results from disintegration of the primary particleswhich must be cleared by the MPS. The mean diameter ofthe particulate dosage form is 3.0–4.5 μm, with a range
949J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
extending upward to 32 μm. The concentration is 5–8×108 microspheres/mL, with a maximal recommended doseof 8.7 mL per contrast study [103]. The maximal numberof particles that can be injected for this approved product istherefore 7×109, or 9.9×107 particles/kg.
Additionally, macroaggregated albumin injection is anapproved product, routinely used in diagnostic imaging. “Theaggregated particles are formed by denaturation of humanalbumin in heating and aggregation process. Each vial contains4–8 million particles. By light microscopy, more than 90% ofthe particles are between 10 and 70 micrometers, while thetypical average size is 20 to 40 micrometers; none is greater than150 micrometers… The suggested range of particle numbersfor a single injection is 200,000–700,000 with the recom-mended number being approximately 350,000” [104].
By way of comparison, the USP b788N microscopic test forparticulate matter in small volume parenteral intravenoussolutions permits only 300 particles N25 μm per unit container[29]. Therefore, conformance of IV drug nanosuspensions to thelimits specified by USP b788N will ensure significant safetyfactors relative to the current practice of pulmonary perfusionof radiographic particulate injections.
The data presented above constitutes a worst case analysis, inthat the size of those particles is considerably larger than that forconventional, modern nanosuspension drug formulations. Thelatter has a mean value, which is far smaller, below 1 μm,compared with those described in the historic literature. Table 3summarizes the maximal IV levels of tolerated doses, reportedin the literature.
3.1.2.2. Effects upon the monocyte phagocytic system. Manyof the animal studies performed in the literature involvedpolystyrene, cross-linked styrene divinyl-benzene, or latexmicrospheres. These particles are biologically inert and non-metabolizable. The persistence of metabolizable drug nanopar-ticulates will be much shorter than the inert particles because ofeither: rapid processing through the phagolysozomes of themacrophages [105], or dissolution of the drug nanoparticleswithin the macrophage and subsequent diffusive migrationextracellularly. Either situation poses much less of burden uponthe macrophages and enables them to cycle faster. If the MPS
Rats, bolus, 2.5×1012 0.4 Well tolerated [129]Dogs, infusion, 1.3×1012 0.4 Well tolerated [130]
becomes overloaded by phagocytic activity, then reticuloen-dothelial blockage could potentially occur [106], but only if thephagocytic overload is continued and heavy [107,108], becausethese cells can digest all biodegradable substances [109].
It has been observed that administration of liposomaldoxorubicin (a cytotoxic agent and macrophage targeter) didnot result in more frequent opportunistic infections in patientswith AIDS-related Kaposi's sarcoma compared to patientstreated with combinations of conventional non-particulateformulations of doxorubicin, bleomycin and vincristine [110]This was explained by a compensatory increase in macrophagenumbers and activity of the organism when subjected to highphagocytic loads [111]. In animal systems, for example,exposure to liposomes results in an initial reduction inmacrophage capacity, which subsequently rises twofold within24–48 h.
Delayed phagocytosis of nanoparticles can be accomplishedby coating with phospholipid–polyethyleneglycol (PEG). Thisreduces the propensity of protein adsorption, and therefore,opsonization, or surface protein-adsorbed triggering of thespecific membrane receptors for phagocytosis by the macro-phage. The phagocytic properties of macrophages couldpotentially be used for slow release of entrapped drugs. ThisIV slow depot release could be utilized to alter the pharma-cokinetic profile of a drug for desirable therapeutics effects.
3.2. Preclinical and clinical applications of intravenousnanoparticles
Nanoparticles typically refer to solid particles with a sizedistribution consisting of a median of around 0.1 to 1 μm. Theparticles can be formulated as crystals stabilized surfactants, oras amorphous particles coated by a layer of an encapsulate(surfactant or other material) or as nanospheres of polymericmatrices with the drug trapped within. When injected intra-venously, the fate of the particles depends on a number ofproperties such as: drug particle dissolution rates; morphologyof particles, type and density of coating; size of the particles.
When the particles are injected into the blood stream they aresubjected to an instantaneous sink condition. Under such asituation the particles may dissolve completely, immediatelyupon injection. The suspension in such cases provides apharmacokinetic profile very similar to a true solution. Oneexample of this case is the intravenous injection of flurbiprofen[74]. The drug itself has a solubility of b10 ppm [112].However when formulated as a nanoparticle and injectedintravenously, the drug dissolved rapidly, leading to similarplasma profile as the solution formulation. Furthermore thedistribution of the drug in various organs was similar as well forthe two formulations tested. The nanoparticles however pro-vided a superior formulation, since the solution required highpH that could potentially cause pain on injection. In this casestudy the particles were stabilized using phospholipids.
Morphology of particles plays an important role on thedissolution behavior of the particles, hence this factor is linkedto the one above. For example, amorphous particles maydissolve rapidly upon injection and show a pharmacokinetic
Fig. 3. Transmission electron micrograph showing itraconazole nanoparticlesendocytized in phagolysosomes of fixed macrophages of the spleen (arrowsshow the particles).
950 J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
profile similar to solution. Crystalline particles on the otherhand may take a longer time to dissolve. This lag would allowthe particle to be recognized as a foreign object by the body'simmune system.
As discussed previously, successful evasion of opsonization[113] enables long circulating particles to have higher chancesof being transported to the region of choice, such as the tumortissue, or a site of inflammation. This approach was exploited inthe liposomal formulation of doxorubicin — Doxil®. Thebiggest clinical benefit of long circulating nanoparticles is forpassive targeting into tumors via a phenomenon termed asenhanced permeation and retention (EPR) effect. Circulatingparticles diffuse preferentially into tumor tissues due to theleaky nature of tumor vasculature. The extent of tumor targetingdepends on the circulation time of the particles, which in turndepends on the type and density of coating. PEG with aminimum molecular weight of 2000 is considered desirable toprovide stealth properties to nanoparticles. Below this chainlength, the PEG chains are too rigid and may not provide thesame protection from opsonin protein adsorption. If the PEGdensity is too low, protein adsorption and subsequent particlephagocytosis is possible. On the other hand, if the PEG densityon the particle is too high, the mobility of the chains may berestricted and hence the protection may be compromised.
The size range of the nanoparticles plays a critical role on itspharmacokinetic fate. The process of phagocytosis is applicableto particles as small as 500 nm, whereas a similar receptor-mediated endocytosis is more generally available to manydifferent kinds of cells. This extends to particles as small as100 nm and probably smaller [114]. For particles greater than300 nm, stealth properties are minimal even when appropriatecoating is present. This is due to the overwhelming propensityfor phagocytosis at higher particle size. Furthermore, there is anupper limit placed upon the size of the particle, permittingdiffusion through the vascular tumor pores. The range of poresizes is 300 nm to 700 nm, depending upon the tumor type, andtherefore targeting particles should be substantially smaller,preferably less than 250 nm.
3.2.1. Preclinical dataTypically, if the particles following IV injected suspension
do not dissolve quickly in blood, they will be swiftly removedfrom circulation leading to a much lower Cmax and a higherAUC than would have obtained following IV injection of thedrug solution of equivalent dose. Following an injection of80 mg/kg itraconazole suspension, drug concentration in theplasma exhibited as precipitous drop subsequent resurgence to aCmax of 2.8 μg/mL, corresponding to approximately 24 h afterinjection [1]. Primarily, the particles are endocytized inphagolysosomes of fixed macrophages in the RES and theitraconazole is released back into the blood. Fig. 3 shows thetransmission electron micrograph (TEM) of itraconazole drugcrystals in macrophages following IV administration to a rat[115]. Drug uptake does not affect cellular viability, and in factmacrophages are able to continue phagocytose other particlesincluding E. coli. In this respect, IV injection of suspensiongains an advantage because toxicity is proportional to Cmax and
efficacy is proportional to AUC. The altered pharmacokineticsprofile seen for the nanosuspension explains the increasedtolerability as compared to the solution formulation in the rat.The LD50 was reported to be higher than 320 mg/kg.
Other the other hand, following IV injection of microparticledantrolene, the drug is released rapidly in an animal study tocounteract hyperthermia within minutes and is completelyeliminated from the blood stream after 24 h [9]. This is anexample of rapid drug release.
3.2.2. Clinical applicationsThe nanoparticle-based product, Abraxane®, approved by
FDA for intravenous administration. Abraxane® is a novelformulation consisting of lyophilized particles with 10% (w/w)paclitaxel and 90% (w/w) albumin. The particle size of thesuspension is about 130 nm [116]. In a Phase I trial, 39 patientswith advanced nonhematologic malignancies were treated atdose levels from 80 to 200 mg/m2 in multiple cycles of weekly30-minute intravenous infusions. No premedication was used inthis study. The maximum tolerated dose observed from thisstudy was higher than the commercial Taxol® formulation.Furthermore this study confirmed that the nanoparticleformulation of paclitaxel eliminates the need for premedication(since the toxic excipient Cremophor EL was not used in theformulation) [117].
Results from a multicenter Phase II study confirmed thefindings from the initial Phase I clinical study. In this expandedstudy, 63 patients with metastatic breast cancer received300 mg/m2 Abraxane® by intravenous infusion over 30 minevery 3 weeks without premedication. An overall response rateof 48% was found for all patients enrolled in this study [118].
951J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
In a pivotal Phase III trial/drug comparison study involving454 breast cancer patients, Taxol® was administered by itsstandard protocol using a 3-hour infusion. Additionally,premedication with steroid and antihistamines was required toalleviate Cremophor related hypersensitivity. Abraxane® on theother hand was administered at higher doses over a shorterduration 30 min, without any premedication. The nanoparticleformulation showed a higher response rate, higher time to tumorprogression, and lower incidence of grade 4 neutropenia.Additional studies are ongoing to combine the paclitaxel–albumin nanoparticles with other chemotherapy agents to attackother cancers. A Pharmacokinetic study utilizing a combinationof Abraxane® and carboplatin, involving 41 patients with solidtumors, indicated response in melanoma, lung, bladder,esophageal, and pancreatic cancer [119]. Another study in-volving combination of Abraxane® with gemcitabine has alsobeen reported [120].
Another intravenous nanoparticle formulation tested inclinical trials is Spartaject™ Busulfan. This formulation con-sists of a sterile powder of busulfan, encapsulated in a mixtureof phospholipids, dimyritoylphosphatidylcholine, and dilaur-oylphosphatidylcholine in a buffer containing mannitol [121].Twelve patients with chronic myeloid leukemia were treated ina Phase I/II clinical trial. The nanoparticle formulationdemonstrated low intra-patient variability compared to theoral formulation. Furthermore, the nanoparticle formulationindicated reduced toxicity compared to other formulations.
Mouton and coworkers discuss the pharmacokinetics ofitraconazole, injected intravenously into human subjects, as acrystalline suspension [27]. The suspension was stabilized usingPluronic 108, and had a mean particle size of 200–300 nm. Itwas surprisingly observed that the half-life of itraconazole as ananosuspension was not significantly higher than that of acyclodextrin-based solution, injected as control. This suggeststhat the particles may have dissolved rapidly upon administra-tion, thus behaving similar to a solution.
Hollow microspheres consisting of a hydrophobic drugdispersed in a biodegradable polymeric matrix has been testedas an approach to create faster dissolving formulations of thedrug. This concept was tested for paclitaxel, in a Phase I clinicaltrial involving 22 patients [121]. The main objective of thestudy was to define the dose-limiting toxicity, maximallytolerated dose and pharmacokinetics. The novel Cremophor-free formulation eliminated the need for corticosteroid pretreat-ment and allowed for rapid intravenous infusion (less than30 min).
Besides small molecules, nanoparticles can also be used ascarriers for intravenous administration of macromolecules. Arecent study conducted at conducted at the University of TexasM. D. Anderson Cancer Center, utilized lipid nanoparticles ascarriers for the delivery of a FUS1 gene [122]. Thirteen patientswere treated with no significant drug-related toxicity. Mediansurvival time for all patients was 14.6 months, which comparedfavorably to a seven-month median survival time for patientsreceiving second line therapy. It was reported that the maximumtolerated dose had not been identified, hence allowing thecontinuation of the study.
3.2.3. Approved IV injectable suspension productsImagent®, a contrast agent, is an injectable suspension of
microspheres that was approved by the FDA in June 2002 for usein patients with suboptimal echocardiograms. It is indicated forimproved ultrasound images of the left ventricular chamberof the heart, as well as improving the delineation of the leftventricular endocardial border. The formulation contains 200mgof Imagent® powder, 9.2 mg 1,2-dimyristoyl-sn-glycero-3-phosphocholine, 2.1 mg poloxamer 188, 75 mg hydroxyethylstarch, 75 mg of sodium chloride and 36 mg sodium phos-phate buffer. In terms of particle size distribution, it has amaximum of 13.7×108 microspheres/mLwith 78.8% of b3 μm,21.0% 3-10 μm and 0.2% N10 μm (upper limit 20 μm) afterreconstitution.
Abelcet® is a currently US marketed amphotericin B lipidcomplex injection. Per package insert, it is an opaque sus-pension formulated per mL with 5 mg of amphotericin B,3.4 mg L-α-dimyristoylphosphatidylcholine, 1.5 mg L-α-dimyristoylphosphatidylglycerol and 9 mg sodium chloride.Abelcet® was reported to provide a less toxic alternative (lessnephrotoxic) to conventional amphotericin B treatment infungal infections without compromising efficacy. In addition,the treatment of invasive fungal infections in patients who areintolerant of or refractory to conventional antifungal therapywas also supported in human study [123].
Abraxane® is the newest approved injectable suspension.The particle size was reported to be 130 nm [124]. Following IVadministration of 260 mg/m2 Abraxane® over 30 min withoutpremedication this suspension was reported to be well tolerated.Significant tumor responses and prolonged disease control weredocumented. The formulation for paclitaxel protein-boundparticles includes 100 mg of paclitaxel and 900 mg of humanalbumin per vial. Paclitaxel is insoluble in water. Humanalbumin is reported to be biodegradation into natural products,lack of toxicity and nonantigenic.
4. Concluding remarks
Nanoparticles have rapidly gained acceptance and interestin intravenous dosage forms. Up to June of 2007, there are over20 companies worldwide pursing the applications of nanotech-nology in drug delivery [125]. While research in this area datesback to 1980s, more relevant human clinical data has beengathered in the past twenty years. There is an increasingdatabase of evidence indicating the safety of injecting drugnanoparticles directly in the blood stream. However, given thecomplexity of this dosage form, significant care has to be takenin production and characterization of the formulation. Choice ofexcipients plays a key role in stability of the particles as well asthe toxicity of the final product. As new techniques andregulatory guidance develop to characterize submicron parti-cles, it is expected that nanoparticles will be used on a morewidely and on a consistent basis, especially for poorly solubledrugs. The possibility of targeted drug delivery has alsoprovided an opportunity to utilize nanoparticle dosage formsfor more complex molecules such as proteins and nucleic acidbased drugs.
952 J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
Acknowledgements
The authors wish to acknowledge the contributions bythe NANOEDGE team members, especially the encourage-ment from Dr. Neervalur Raghavan, Dr. Jeffery Wilhelm,Dr. Theodore Roseman, Dr. Philip Carter and Mr. ThomasGonyon.
References
[1] J. Kipp, The role of solid nanoparticle technology in the parenteraldelivery of poor water-soluble drugs, Int. J. Pharm. 284 (2004) 109–122.
[2] C. Lipinski, Drug-like properties and the cause of poor solubility andpoor permeability, J. Pharmacol. Toxicol. Methods 44 (2000) 235–249.
[3] C. Lipinski, Poor aqueous solubility— an industry wide problem in drugdiscovery, Am. Pharm. Rev. 5 (2002) 82–85.
[4] K. Gupta, Solutions and phase equilibria, in: A. Gennaro (Ed.),Remington: The Science and Practice of Pharmacy, 20th Ed., LippincottWilliams & Wilkins, Baltimore, 2000, pp. 208–209.
[5] S. Yakowsky, Solubility and Solubilization in Aqueous Media, OxfordUniversity Press, New York, 1999, pp. 67, 321–396, 426, 431.
[6] B. Rabinow, Nanosuspensions in drug delivery, Nat. Rev. Drug Discov.3 (2004) 785–796.
[7] M. Francois, E. Snoeckx, P. Putteman, F.Wouters, E. De Proost, U. Delaet,J. Peeters, M. Brewster, A mucoadhesive, cyclodextrin-based vaginalcream formulation of itraconazole, AAPS PharmSci 5 (2003) Article 5.
[8] J. Zuidema, F. Pieters, G. Duchateau, Release and absorption rate aspects ofintramuscularly injected pharmaceuticals, Int. J. Pharm. 47 (1988) 1–12.
[9] S. Pace, G. Pace, I. Parikh, A. Mishra, Novel injectable formulations ofinsoluble drugs, Pharm. Technol. 23 (1999) 116–134.
[10] P. Borm, F. Klaessig, T. Landry, B. Moudgil, J. Pauluhn, K. Thomas,R. Trottier, S. Wood, Research strategies for safety evaluation ofnanomaterials, Part V: role of dissolution in biological fate and effectsof nanoscale particles, Toxicol. Sci. 90 (2006) 23–32.
[11] P. Bummer, Interfacial phenomena, in: A. Gennaro (Ed.), Remington:The Science and Practice of Pharmacy, 20th Ed., Lippincott Williams &Wilkins, Baltimore, 2000, p. 285.
[12] L. Gould, A. Lansley, M. Brown, B. Forbes, G. Martin, Mitigation ofsurfactant erythrocyte toxicity by egg phosphatidylcholine, J. Pharm.Pharmacol. 52 (2000) 1203–1209.
[13] S. Apte, S. Ugwu, A review and classification of emerging excipients inparenteral medications, Pharm. Technol. 27 (2003) 46–60.
[14] J. Adler, P. Singh, A. Patist, Y. Rabinovixh, D. Shah, B. Moudgil,Correlation of particulate dispersion stability with the strength of self-assembled surfactant films, Langmuir, 16 (2000) 7255–7262.
[15] D. Carthew, G. Buckton, G. Parsons, S. Poole, The effect of temperatureon the surface nature of an adsorbed layer of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymers, Pharm. Res. 13 (1996)1730–1733.
[16] S. Chasteigner, G. Cave, H. Fessi, J. Devissaguet, F. Puisieux, Freeze-drying of itraconazole loaded nanosphere suspensions: a feasibility study,Drug Dev. Res. 38 (1996) 116–124.
[17] D. Owens, N.A. Peppas, Opsonization, biodistribution, and pharmacoki-netics of polymeric nanoparticles, Int. J. Pharm. 307 (1) (2006 Jan 3) 93–102.
[18] S. Moghimi, A. Hunter, J. Murray, Long-circulating and target-specificnanoparticles: theory to practice, Pharmacol. Rev. 53 (2001) 283–318.
[19] K. Welin-Berger, B. Bergenstahl, Inhibition of Ostwald ripening in localanesthetic emulsions by using hydrophobic excipients in the dispersephase, Int. J. Pharm. 200 (2000) 249–260.
[20] J. Mullin, Crystallization, 4th Ed., Elsevier, Oxford, 2004, pp. 320–322.[21] J. Swarbrick, J. Rubino, O. Rubino, Coarse dispersion, in: A. Gennaro
(Ed.), Remington: The Science and Practice of Pharmacy, 20th Ed.,Lippincott Williams & Wilkins, Baltimore, 2000, p. 322.
[22] E. Merisko-Liversidge, G. Liversidge, E. Cooper, Nanosizing: aformulation approach for poorly-water-soluble compounds, Eur. J.Pharm. Sci. 18 (2003) 113–120.
[23] N. Scholer, C. Olbrich, K. Tabatt, R. Muller, H. Hahn, O. Liesefeld,Surfactant, but not the size of solid nanoparticles (SLN) influencesviability and cytokine production of macrophages, Int. J. Pharm. 221(2001) 57–67.
[24] R. Muller, D. Ruhl, S. Runge, K. Schulze-Forster, W. Mehnert,Cytotoxicity of solid lipid nanoparticles as a function of the lipid matrixand the surfactant, Pharm. Res. 14 (1997) 458–462.
[25] J. Riess, M. Le Blanc, Perfluorocompounds as blood substitutes, Angew.Chem. 17 (1978) 621–634.
[26] G. Dumortier, J. Grossiord, F. Agnely, J. Chaumeil, A review ofpoloxamer 407 pharmaceutical and pharmacological characteristics,Pharm. Res. 23 (2006) 2709–2728.
[27] J. Mouton, A. van Peer, K. de Beule, A. van Vliet, J. Donnelly, P. Soons,Pharmacokinetics of itraconazole and hydroxyitraconazole in healthysubjects after single and multiple does of a novel formulation,Antimicrob. Agents Chemother. 50 (2006) 4096–4102.
[28] H. Schroeder, G. Simmons, P. DeLuca, Distribution of radiolabeledsubvisible microspheres after intravenous administration to beagle dogs,J. Pharm. Sci. 67 (1978) 504–507.
[29] Chapter 788, Particle matter in injections, The United State Pharmacopeia,The National Formulary, USP30/NF25, vol. 1, The United StatePharmacopeial Convention, Rockville, 2007, pp. 321–327.
[30] H. Lehr, J. Brunner, R. Rangoonwala, C. Kirkpatrick, Particulate mattercontamination of intravenous antibiotics aggravates loss of functionalcapillary density in post ischemic striated muscle, Am. J. Respir. Crit.Care Med. 165 (2002) 514–520.
[31] W. Oh, M. Mital, Fat embolism: current concepts of pathogenesis,diagnosis, and treatment, Orthop, Clin. North Am. 9 (1978) 769–779.
[32] J. Orenstein, N. Sato, B. Arcon, B. Buchholz, S. Bloom, Microemboliobserved in deaths following cardiopulmonary bypass surgery: siliconeantifoam agents and polyvinyl chloride tubing as sources of emboli,Human Pathol. 13 (1982) 1082–1090.
[33] A. Burton, L. Rhines, E. Mendel, Vertebroplasty and kyphoplasty: acomprehensive review, Neurosurg. Focus 18 (2005) 1–9.
[34] F. Douglas, K. Fafilmout, N. Patt, Foreign particle embolism in drugaddicts: respiratory pathophysiology, Ann. Intern.Med. 75 (1971) 865–872.
[35] S. Ward, L. Heyneman, P. Reittner, E. Kazerooni, J. Godwin, N. Müller,Talcosis associated with IV abuse of oral medications: CT findings, Am.J. Roentgenol. 174 (2000) 789–793.
[36] J. Pare, G. Cote, R. Fraser, Long-term follow-up of drug abusers withintravenous talcosis, Am. Rev. Respir. Dis. 139 (1989) 233–241.
[37] E. Overland, A. Nolan, P. Hopewell, Alteration of pulmonary function inintravenous drug abusers, Am. J. Med. 68 (1980) 231–237.
[38] D. Sieniewicz, A. Nidecker, Conglomerate pulmonary disease: a form oftalcosis in intravenousmethadone abusers, Am. J. Roentgenol. 135 (1980)697–702.
[39] K. Falchuk, L. Peterson, B. McNeil, Microparticle-induced phlebitis, itsprevention by in-line filtration, N. Engl. J. Med. 312 (1985) 78–82.
[40] T. Taniguchi, K. Yamamoto, T. Kobayashi, Precipitate formed bythiopentone and vecuronium cause pulmonary embolism, Can. J. Anaesth.45 (1998) 347–351.
[41] S. Yalkowsky, J. Krzyzaniak, G. Ward, Formulation-related problemsassociated with intravenous drug delivery, J. Pharm. Sci. 87 (1998)787–796.
[42] L. Garavilla, N. Peltier, E. Merisko-Liversidge, Controlling the acutehemodynamic effects associated with IV administration of particulatedrug dispersions in dogs, Drug Dev. Res. 37 (1996) 86–96.
[43] T. Barber, Pharmaceutical Particle Matter Analysis and Control,Interpharm Press, Buffalo Grove, Illinois, 1993, pp. 50–142, 266–349,294–303, 470–486.
[44] D. Neuberger, J. Wong, Suspension for intravenous injection: imageanalysis of scanning electron micrographs of particles to determine sizeand volume, PDA J. Pharm. Sci. Technol. 59 (2005) 187–199.
[45] J. Wong, P. Papadopoulos, J. Werling, C. Rebbeck, M. Doty, J. Kipp,J. Konkel, D. Neuberger, Itraconazole suspension for intravenousinjection: determination of the real component of complete refractiveindex input for static light scattering particle sizing instrument, PDAJ. Pharm. Sci. Technol. 60 (2006) 302–313.
953J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
[46] A. Tinke, K. Vanhoutte, R. De Maesschalck, S. Verheyen, H. De Winter,A new approach in the prediction of dissolution behavior of suspendedparticles by means of their particle size distribution, J. Pharm. Biomed.Anal. 39 (2005) 900–907.
[47] R. Kelly, S. Lerke, Particle size measurement techniques selection withinmethod development in the pharmaceutical industry, Am. Pharm. Rev. 8(2005) 72–81.
[48] A. Hickey, N. Concessio, Descriptors of irregular particle morphologyand powder properties, Adv. Drug Deliv. Rev. 26 (1997) 29–40.
[49] F. Etzler, R. Deanne, Particle size analysis: a comparison of variousmethods II, Part. Part. Syst. Charact. 14 (1997) 278–282.
[50] Guide to Selecting Refractive Index, Particle Size Distribution AnalyzerTechnical Note, TN118, Horiba Instruments, Inc., Irvine, CA, , 2004.
[51] S. Toongsuwan, H. Chang, L. Li, D. Stephens, H. Plichta-Mahmoud,Particle size determination of a three-component suspension using a laser-scattering particle size distribution analyzer, Drug Dev. Ind. Pharm. 26(2000) 895–900.
[52] D. Driscoll, F. Etzler, T. Barber, J. Nehne, W. Niemann, B. Bistrian,Physicochemical assessments of parenteral lipid emulsions: lightobscuration versus laser diffraction, Int. J. Pharm. 219 (2001) 21–37.
[53] K. Mattison, A. Morfesis, M. Kaszuba, A Primer on Particle Sizing usingDynamic Light Scattering, American Biotechnology Laboratory, Decem-ber, 2003, pp. 20–23.
[54] V. Bloomfield, Static and dynamic light scattering from aggregatingparticles, Biopolymers 54 (2000) 168–172.
[55] H. Műller, Automated determination of particle-size distributions ofdispersions by analytical ultracentrifugation, Colloid Polym. Sci. 267(1989) 1113–1116.
[56] D. Barber, J. Keuter, K. Kravig, A logical stepwise approach to laserdiffraction particle size distribution analysis development and validation,Pharm. Dev. Technol. 3 (1998) 153–161.
[57] V. Koster, P. Kuks, R. Lange, H. Talsma, Particle size in parenteral fatemulsions, what are the true limitations? Int. J. Pharm. 134 (1996) 235–238.
[58] D. Driscoll, Lipid injectable emulsions: pharmacopeial and safety issues,Pharm. Res. 23 (2006) 1959–1969.
[59] D. Driscoll, Stability and compatibility assessment techniques for totalparenteral nutrition admixtures: setting the bar according to pharmaco-peial standard, Curr. Opin. Clin. Nutr. Metab. Care 8 (2005) 297–303.
[60] In-Process Revision, b729N Globule Size Distribution in Lipid InjectableEmulsions, Pharmaceutical Forum, Vol. 31 (5), The United States Pharma-copeial Convention, Rockville, September–October, 2005, 1448–1453.
[61] D. Driscoll, J. Nehne, H. Peters, K. Klűtsch, B. Bistrian, W. Niemann,Physical assessments of lipid injectable emulsions via microscopy: acomparison methods proposed in United States pharmacopoeia chapterb729N, Int. J. Pharm. Compd. 10 (2006) 309–315.
[62] Y. Tian, L. Li, Light-scattering method in particle size analysis ofparenteral emulsions, Drug Dev. Ind. Pharm. 24 (1998) 275–280.
[63] D. Driscoll, M. Parikh, A. Silvestri, K. Klűtsch, B. Bistrian, J. Nehne,Establishing a stability window for medium-chain and long-chain-triglyceride lipid-based total nutrient admixtures using USP standards,Am. J. Health-Sys. Pharm. 63 (2006) 2135–2143.
[64] D. Driscoll, Lipid injectable emulsions, Nutr. Clin. Prac. 21 (2006) 381–386.[65] Injectable Preparations, British Pharmacopoeia, vol. II, Her Majesty's
Stationary Office, London, 1980, pp. 578–580.[66] W. Burnham, P. Hansrani, C. Knott, C. Cook, S. Davis, Stability of a fat
emulsion based intravenous feeding mixture, Int. J. Pharm. 13 (1983) 9–22.[67] C. Schwarz, W. Mehnert, J. Lucks, R. Müller, Solid lipid nanoparticles
(SLN) for controlled drug delivery. I. Production, characterization andsterilization, J. Control. Release 30 (1994) 83–96.
[68] T. Gonyon, P. Patel, H. Owen, A. Dunham, P. Carter, Physiochemicalstability of lipid injectable emulsions: correlating changes in large globuledistributions with phase separation behavior, Int. J. Pharm. 343 (2007)208–219.
[69] Chapter 905, Uniformity of Dosage Units, The United State Pharmaco-peia, The National Formulary, USP30/NF25, Vol. 1, The United StatePharmacopeial Convention, Rockville, 2007, pp. 379–385.
[70] E. Barash, A. Newman, S. Bates, S. Comella, Amorphous pharmaceu-ticals, AAPS Newsmagazine, June, 2006, p. 30.
[71] B. Hancock, G. Zografi, Characteristics and significance of the amorphousstate in pharmaceutical systems, J. Pharm. Sci. 86 (1997) 1–12.
[72] S. Kim, C. Wei, S. Kiang, Crystallization process development of an activepharmaceutical ingredient and particle engineering via the use of ultra-sonics and temperature cycling, Org. Process Res. Dev. 7 (2003) 997–1001.
[73] D. Ende, S. Brenek, Strategies to control particle size during crystal-lization process, Am. Pharm. Rev. 7 (2004) 98–104.
[74] M. Clement, W. Pugh, I. Parikh, Tissue distribution and plasma clearanceof a novel microcrystal-encapsulated flurbiprofen formulation, Pharma-cologist 34 (1992) 204.
[75] J. Oldshue, Mixing of solid–liquid suspensions, J. Pharm. Sci. 50 (1961)523–530.
[76] J. Oldshue, N. Nerbst, T. Post, A Guide to Fluid Mixing, Lightnin, NewYork, 1995, pp. 1–27.
[77] F. Alvarez Nunez, S, Yalkowsky, Foaming activity and pKa of somesurface active compounds, Int. J. Pharm. 151 (1997) 193–199.
[78] L. Block, Process scale-up for pharmaceutical liquids and semisolids,Am. Pharm. Rev. 3 (2000) 30–33.
[79] C. Geankoplis, Transport Processes and Unit Operations, 3rd Ed.,Prentice-Hall, Englewood Cliffs, 1978, pp. 140–153.
[80] A. Nienow, The suspension of solid particles, in: H. Harnby, M. Edwards,A. Nienow (Eds.), Mixing in the Process Industries, 2nd Ed., Butterwoth-Heinemann, Oxford, 2000, pp. 364–393.
[81] Y. Chien, P. Przybyszewski, E. Shami, Syringeability of nonaqueousparenteral formulations — development and evaluation of a testingapparatus, PDA J. Pharm. Sci. Technol. 35 (1981) 281–284.
[82] Chapter 1211, Sterilization and Sterility Assurance of CompendialArticles, The United State Pharmacopeia, The National Formulary,USP30/NF25, Vol. 1, The United State Pharmacopeial Convention,Rockville, 2007, pp. 669–674.
[83] H. Dulmage, J. Correa, J. Martinez, Coprecipitation with lactose as ameans of recovering the spore–crystal complex of Bacillus thuringiensis,J. Invertebr. Pathol. 15 (1970) 15–20.
[84] C. Abbott, J. Cockton, W. Jones, Resistance of crystalline substances togas sterilization, J. Pharm. Pharmacol. 8 (1956) 709–720.
[85] J. Doyle, R. Ernst, Resistance of Bacillus subtilis var. niger sporesoccluded in water-insoluble crystals to three sterilization agents, Appl.Microbiol. 15 (1967) 726–730.
[86] C. Mullican, R. Hoffman, Dry heat or gaseous chemical resistance ofBacillus subtilis var. niger spores included within water-insolublecrystals, Appl. Microbiol. 16 (1968) 1110–1113.
[87] J. Wong, P. Papadopoulos, C. Rebbeck, S. Schwabe, G. Lischewski,J.Melchert,W.Kuu, T.Agostinelli, T. Smith, G. Brame, R. Lynn, D. Hepler,Effect of terminal sterilization by irradiation on amber type I and typeIII glass containers containing veterinary oxytetracycline suspension, PDAJ. Pharm. Sci. Technol., 58 (2004) 6–14.
[88] B. Reid, Gamma processing technology: an alternative technology forterminal sterilization of parenterals, PDA J. Pharm. Sci. Technol. 49(1995) 83–89.
[89] J. Zheng, H. Bosch, Sterile filtration of NanoCrystal™ drug formulations,Drug Dev. Ind. Pharm. 23 (1997) 1087–1093.
[90] N. Moller, V. Jensen, Studies on particle size problems-V. Surface areastabilities of micronized powders in relation to humidity and heatsterilization, Dansk Tidsskr. Farm. 44 (1970) 301–310.
[91] R. Friedman, S. Mahoney, Risk factors in aseptic processing, Am. Pharm.Rev. 6 (2003) 44–47.
[92] Chapter 71, Sterility Tests, The United State Pharmacopeia, The NationalFormulary, USP30/NF25, Vol. 1, The United State PharmacopeialConvention, Rockville, 2007, pp. 97–102.
[93] H. Toguchi, Sterility assurance of microspheres, J. Control. Release 62(1999) 51–55.
[94] Chapter 85, Bacterial Endotoxins Test, The United State Pharmacopeia,The National Formulary, USP30/NF25, Vol. 1, The United StatePharmacopeial Convention, Rockville, 2007, pp. 109–113.
[95] Chapter 151, Pyrogen Test, The United State Pharmacopeia, The NationalFormulary, USP30/NF25, Vol. 1, 2007, pp. 135–136.
[96] J. Margolis, J. McDonald, R. Heuser, P. Klinke, R. Waksman, R. Virmani,N. Desai, D. Hilton, Systemic nanoparticle paclitaxel (NAB-paclitaxel)
954 J. Wong et al. / Advanced Drug Delivery Reviews 60 (2008) 939–954
for in-stent restenosis I (SNAPIST-I): a first-in-human safety and dose-finding study, Clin. Cardiol. 30 (2007) 165–170.
[97] A. Olszanski, L. Lewis, C. Mita, R. Walovitch, R. Perez, D. Tuck,E. Rowinsky, Phase 1 and pharmacokinetic study of AI-850, a novelmicroparticle hydrophobic drug delivery system (HDDS) for pac-litaxel, 2004 ASCO Annual Meeting Proceedings (Post-MeetingEdition), J. Clin. Oncol. 22 (2004, July 15 Supplement) 2048.
[98] J. Straub, D. Chickering, J. Lovely, H. Zhang, B. Shah, W. Waud,H. Bernstein, Intravenous hydrophobic drug delivery: a porous par-ticle formulation of paclitaxel (AI-850), Pharm. Res. 22 (2005)347–355.
[99] M. Kanke, G. Simmons, D. Weiss, B. Bivins, P. DeLuca, Clearanceof 41Ce labeled microspheres from blood and distribution in specificorgans following intravenous and intraarterial administration in beagledogs, J. Pharm. Sci. 69 (1980) 755–762.
[100] J. Singer, L. Adlersberg, E. Hoenig, E. Ende, Y. Tchorsch, Radiolabeledlatex particles in the investigation of phagocytosis in vivo: clearancecurves and histological observations, J. Reticuloendothel. Soc. 6 (1969)561–589.
[101] R. Gesler, P. Garvin, B. Klamer, R. Robinson, C. Thompson, et al., Thebiological effects of polystyrene latex particles administered intrave-nously to rats—a collaborative study, Bull. Parenter. Drug Assoc. 27(1973) 101–113.
[102] H. Schroeder, G. Simmons, P. Deluca, Distribution of radiolabeledsubvisible microspheres after intravenous administration to beagle dogs,J. Pharm. Sci. 67 (1978) 504–507.
[103] OPTISON™ (Perflutren Protein-Type A Microspheres for Injection,USP) Product Description, Amersham Health Inc. , June 2003.
[104] DraxImage MAA Kit for the preparation of Technetium Tc99m AlbuminAggregated Injection. Product insert, , February 2002.
[105] J. Kreuter, Nanoparticles, in: J. Kreuter (Ed.), Colloidal Drug DeliverySystems, Marcel Dekker, New York, 1994, pp. 219–315.
[106] T. Daemen, G. Hofstede, M. ten Kate, I. Bakker-Woudenbert, G.Scherphof, Liposomal doxorubicin-induced toxicity: depletion andimpairment of phagocytic activity of liver macrophages, Int. J. Cancer61 (1995) 716–721.
[107] E. van Etten, M. ten Kate, S. Snijders, I. Bakker-Woudenberg,Administration of liposomal agents and blood clearance capacity of themononuclear phagocyte system, Antimicrob. Agents Chemother. 42(1998) 1677–1681.
[108] I. Bakker-Woudenberg, M. ten Kate, G. Storm, E. van Etten,Administration of liposomal agents and the phagocytic function of themononuclear phagocytic system, Int. J. Pharm. 162 (1998) 5–10.
[109] L. Pesko, Physiological consequences of injected particulates, in: J.Z.Knapp, T.A. Barber, A. Lieberman (Eds.), Liquid- and Surface-BorneParticle Measurement Handbook, Marcel Dekker, New York, 1996,pp. 661–686.
[110] J. Bogner, U. Kronawitter, B. Rolinski, K. Truebenbach, F. Goebel,Liposomal doxorubicin in the treatment of advanced AIDS-relatedKaposi sarcoma, J. Acquir. Immune Defic. Syndr. 7 (1994) 463–468.
[111] T. Daemen, J. Regts, M. Meesters, M. ten Kate, I. Bakker-Woudenberg,G. Scherphof, Toxicity of doxorubicin entrapped within long-circulatingliposomes, J. Control. Release 44 (1997) 1–9.
[112] University of Alberta Drug Bank, July 12th, 2007, http://redpoll.pharmacy.ualberta.ca/drugbank/extrIndex.htm.
[113] B. Rabinow, M. Chaubal, Injectable nanoparticles for efficient drugdelivery, in: R. Gupta, J. Kompella (Eds.), Nanoparticle Technology forDrug Delivery, Marcel Dekker, New York, 2006.
[114] A. Rupper, J. Cardelli, Regulation of phagocytosis and endophagosomaltrafficking pathways in Dictyostelium discoideum, Biochim.Biophys.Acta 1525 (2001) 205–216.
[115] B. Rabinow, J. Kipp, P. Papadopoulos, J. Wong, J. Glosson, J. Gass,C. Sun, T. Wielgos, R. White, C. Cook, K. Barker, K. Wood,Itraconazole IV nanosuspension enhances efficacy through alteredpharmacokinetics in the rat, Int. J. Pharm. 339 (2007) 251–260.
[116] D. Nyman, K. Campbell, E. Hersh, K. Long, K. Richardson, V. Trieu,N. Desai, M. Hawkins, D. von Hoff, Phase I and pharmacokineticstrial of ABI-007, a novel nanoparticle formulation of paclitaxel inpatients with advanced nonhematologic malignancies, J. Clin. Oncol. 1(2005) 7785–7793.
[117] N. Ibrahim, N. Desai, S. Legha, P. Soon-Shiong, R. Theriault, E. Rivera,B. Esmaeli, S. Ring, A. Bedikian, G. Hortobagyi, J. Ellerhorst, Phase Iand pharmacokinetic study of ABI-007, a Cremophor-free, protein-stabilized, nanoparticle formulation of paclitaxel, Clin. Cancer Res. 8(2002) 1038–1044.
[118] N. Ibrahim, B. Samuels, R. Page, D. Doval, K. Patel, S. Rao, M. Nair,P. Bhar, N. Desai, G. Hortobagyi, Multicenter phase II trial of ABI-007,an albumin-bound paclitaxel, in women with metastatic breast cancer,J. Clin. Oncol. 23 (2005) 6019–6026.
[119] T. Stinchcombe,M. Socinski, C.Walko, B. O'neil, F. Collichio, A. Ivanova,H. Mu, M. Hawkins, R. Goldberg, C. Lindley, E. Claire Dees, Phase Iand pharmacokinetic trial of carboplatin and albumin-bound paclitaxel,ABI-007 (Abraxane®) on three treatment schedules in patients with solidtumors, Cancer Chemother. Pharmacol. 60 (2007) 759–766.
[120] A. Moreno-Aspitia, E. Perez, North Central Cancer Treatment GroupN0531: phase II trial of weekly albumin-bound paclitaxel (ABI-007;Abraxane®) in combination with gemcitabine in patients with metastaticbreast cancer, Clin. Breast Cancer 6 (2005) 361–364.
[121] E. Olavarria, M. Hassan, A. Eades, C. Nilsson, A. Timms, J. Matthews,C. Craddock, E. Kanfer, J. Apperley, J. Goldman, A phase I/II study ofmultiple-dose intravenous busulfan as myeloablation prior to stem celltransplantation, Leukemia 14 (2000) 1954–1959.
[122] Introgen Company Press Release, dated April 17, 2007. Introgen'sIntravenous Nanoparticle Gene Therapy Shows Activity in Stage IVLung Cancer Patients (cited on Introgen company website, http://www.introgen.com).
[123] T. Walsh, J. Hiemenz, N. Seibel, J. Perfect, G. Horwith, L. Lee, J. Silber,M. DiNubile, A. Reboli, E. Bow, J. Lister, E. Anaissie, AmphotericinB lipid complex for invasive fungal infections: analysis of safety andefficacy in 556 cases, Clin. Infect. Dis. 26 (1998) 1383–1396.
[124] M. Green, G. Manikhas, S. Orlov, B. Afanasyev, A. Makhson, P. Bhar,M. Hawkins, Abraxane, a novel Cremophor-free, albumin-boundparticle form of paclitaxel for the treatment of advanced non-small-cell lung cancer, Ann. Oncol. 17 (2006) 1263–1268.
[125] P. van Arnum, Nanotechnology advances in drug delivery, Pharm.Technol. 31 (2007) 48, 50, 52.
[126] D. Wilkins, P. Meyers, Studies on the relationship between theelectrophoretic properties of colloids and their blood clearance andorgan distribution in the rat, Br. J. Exp. Pathol. 47 (1966) 568–576.
[127] M. Schoenberg, P. Gilman, V. Mumaw, R. Moore, The phagocytosis ofuniform polystyrene latex particles by the reticulo-endothelial system inthe rabbit, Br. J. Exp. Pathol. 42 (1961) 486–495.
[128] J. Slack, M. Kanke, G. Simmons, P. DeLuca, Acute hemodynamic effectsand blood pool kinetics of polystyrene microspheres followingintravenous administration, J. Pharm. Sci. 70 (1981) 660–664.
[129] J. Gass, Pathobiology, Baxter Healthcare Corporation, personalcommunication.
[130] J. Gass, Pathobiology, Baxter Healthcare Corporation, personalcommunication.
