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IJPRD, 2011; Vol 4(06): August-2012 (137 152) International Standard Serial Number 0974 9446
Available online on www.ijprd.com
137
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NANOEMULSIONS AN EMERGING TREND: A REVIEW
R.B.Desi reddy*1,
Ch.T. Lalitha kumari1, G.Naga sowjanya
1, S.L.Sindhuri
1, P.Bandhavi
1
1 Nalanda Institute of Pharmaceutical sciences, Kantepudi, Sattenapalli, India
ABSTRACT
Nanoemulsions are one of the emerging trends in targeted &
controlled drug delivery systems . Nanoemulsions are clear,
thermodynamically stable, isotropic liquid mixtures of oil,
water,surfactant and co-surfactant. These are oil-in-water (o/w)
type of emulsions with the average droplet size ranging from 5nm
to 100 nm. Reduction in droplet size to nanoscale leads to change
in physical properties such as optical transparency & unusual
elastic behavior. Nanoemulsions have widespread applications in
different fields such as pharmaceutics, food technology .
Nanoemulsion offers a promising vehicle for increasing the
aqueous solubility of poorly water-soluble drugs considerably,
which is usually necessary for parenteral application.
Nanoemulsions have many advantages, for instance, enhance
drug solubility, perfect thermodynamic stability, ease of
manufacturing and permeation over conventional formulations
that convert them to important drug delivery systems.
Nanoemulsion can improve transdermal delivery of lipophilic and
hydrophilic compound with different mechanisms. The design &
development of nanoemulsions aimed at controlling or improving
required bioavailability levels of therapeutic agents.. This review
mainly discussed about the importance of nanoemulsions over
other dosage forms, preparation methods ,current state of
nanoemulsions in the delivery of drugs and other bioactives and
characterization of nanoemulsions, applications.
KEYWORDS : Nanoemulsion, parenteral, Preparation,
Characterization, Application in Drug Delivery.
Correspondence to Author
R.B.Desi reddy
Nalanda Institute of Pharmaceutical
sciences, Kantepudi, Sattenapalli,
India
Email: [email protected]
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
Available online on www.ijprd.com
138
INTRODUCTION
Nanoemulsions are non-toxic lipid droplets with a
few hundred nanometers in diameter and made
from surfactants approved for human consumption
and common food substances that are 'Generally
Recognized as Safe' (GRAS) by the FDA. These
emulsions are easily produced in large quantities
by mixing a water-immiscible oil phase into an
aqueous phase with a high-stress, mechanical
extrusion process that is available worldwide. This
process yields a uniform population of droplet
particles that are stable for years even at elevated
temperatures.
The various nanoformulations are : Nanoemulsions
(NE) (submicron sized emulsions), nanosuspensions
(submicron sized suspensions), nanospheres (drug
nanoparticles in polymer matrix), nanotubes
(sequence of nanoscale C60 atoms arranged in a
long thin cylindrical structure), nanoshells
(concentric sphere nanoparticles consisting of a
dielectric core and a metal shell), nanocapsules
(encapsulated drug nanoparticles), lipid
nanoparticles (lipid monolayer enclosing a solid
lipid core) and dendrimers (nanoscale three-
dimensional macromolecules of polymer).
Nanoemulsions are submicron sized emulsions that
are under extensive investigation as drug carriers
for improving the delivery of therapeutic agents.
The small size of the particles in these kinds of
delivery systems (r < 100 nm) means that they have
a number of potential benefits for certain
applications: enhanced long-term stability, high
optical clarity and increased bioavailability.
Nanoemulsions are increasingly being utilized in
food and pharmaceutical industries to encapsulate,
protect, and deliver lipophilic bioactive
components.
Nanoemulsions are formed when the interfacial
tension at the oil/water interface is brought to a
very low level and the interfacial layer is kept
highly flexible and fluid. These two conditions are
usually met by a careful and precise choice of the
components and of their respective proportions
and by the use of a co-surfactant which brings
flexibility to the oil/water interface. These
conditions lead to a thermodynamically optimised
structure, which is stable as opposed to
conventional emulsions and does not require high
input of energy (i.e. through agitation) to be
formed.
Components of Nano Emulsion
The three main components of Nanoemulsions are
as follows:
1. Oil (Table 1)
2. Surfactant/Co-surfactant (Table 2)
3. Aqueous phase (Table 3)
Table 1. List of oils used in nanoemulsions
Name Chemical Name
Captex 355 Glyceryl
Tricaorylate/Caprate
Captex 200 Propylene
Dicaprylate/Dicaprate Glycol
Captex 8000 Glyceryl Tricaprylate
(Tricaprylin)
Witepsol 90:10 % w/w c12 Glyceride
tri: diesters
Myritol 318 c8/c10 triglycerides
Isopropyl myristate Myristic acid isopropyl ester
Table 2. List of Surfactant used in nanoemulsions
S.No Solubilizing agents, surfactants, emulsifying
agents adsorption enhancers
1 Capryol 90
2 Gelucire 44/14, 50/13
3 Cremophor RH 40
4 Imwitor 191, 308(1), 380, 742, 780 K, 928,
988
5 Labrafil M 1944 CS, M 2125 CS
6 Lauroglycol 90
7 PEG MW > 4000
8 Plurol Oleique CC 497
9 Poloxamer 124 and 188
10 Softigen 701, 767
11 Tagat TO
12 Tween 80
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
Available online on www.ijprd.com
139
Table 3. List of Co-Surfactant used in
nanoemulsions
Microemulsions are used for controlled release and
targeted delivery of different pharmaceutics
agents. For instance, microemulsions were used to
deliver oligonucleotides (small fragments of DNA)
specifically to ovarian cancer cells. In contrast to
microemulsions, Nanoemulsions consist in very
fine oil-in-water dispersions, having droplets
diameter smaller than 100 nm. Compared to
microemulsions, they are in a metastable state and
their structure depends on the history of the
system. Nanoemulsions are very fragile systems.
The nanoemulsions can find applications in skin
care due to their good sensorial properties (rapid
penetration, merging textures) and their
biophysical properties (especially their hydrating
power). This technology has a great advantage over
the other dosage forms that the formulation can be
delivered by various routes including oral , ocular
and transdermal .
Nanoemulsions have broad-spectrum
antimicrobial activity against bacteria, enveloped
viruses, fungi, protozoa and spores, due to their
ability to lyse these organisms. In contrast, studies
of nanoemulsions in animals have shown these
compounds to be very well tolerated on the skin
and mucous membranes. These attributes provide
a broad therapeutic index when the nanoemulsions
are used in humans as topical treatments for
disorders including Herpes Labialis, cutaneous
fungal infections, vaginitis, and respiratory
infections. This material holds such unique promise
and low risk that the FDA allowed Phase II Clinical
Trials for the treatment of Herpes Labialis with
Good Manufacturing Procedures (GMP)
nanoemulsion to be conducted.
A B
A:Microemulsions,B:Nanoemulsions
Preparation methods of Nanoemulsions
Several methods have been suggested for the
preparation of nanoemulsion. The basic objectives
of the nanoemulsion preparation is to achieve the
droplet size range of 100-600 nm and another is to
provide the stability condition. Formation of
nanoemulsion system required a high amount of
energy. This energy can be provided either by
mechanical equipment or the chemical potential
inherent within the component . Here some
methods are discussed which are freely used for
the nanoemulsion preparation.
1. Phase inversion method :
In this method fine dispersion is obtained by
chemical energy resulting of phase transitions
taking place through emulsification path. The
adequate phase transitions are produced by
varying the composition at constant temperature
or by varying the temperature at constant
composition. Phase inversion temperature (PIT)
method was introduced by Shinoda et al. based on
the changes of solubility of polyoxyethylene type
surfactant with temperature. This surfactant
becomes lipophilic with increase in temperature
due to dehydration of polymer chain. But at low
temperature, the surfactant monolayer has a large
positive spontaneous curvature forming oil-swollen
S.No Co Surfactant
1 TranscutolP
2 Glycerin,Ethyle
ne glycol
3 Propylene
glycol
4 Ethanol
5 Propanol
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
Available online on www.ijprd.com
140
micellar solution phase .
2.Sonication method:
Sonication method is another best way to prepare
nanoemulsion. In this method the droplet size of
conventional emulsion are reduced with the help
of sonication mechanism. This method is not
suitable for large batches, only small batches of
nanoemulsion can be prepared by this method .
Sonication method
3.Highpressurehomogenizer:
This method is performed by applying a high
pressure over the system having oil phase, aqueous
phase and surfactant or co-surfactant. The
pressure is applied with the help of a special
equipment know as homogenizer. There are some
problems which are associated with homogenizer
such as poor productivity, component
deterioration due to difficult mass production and
generation of much heat. With this method only oil
in water (o/w) liquid nanoemulsion of less than
20% oil phase can be prepared and cream
nanoemulsion of high viscosity or hardness with a
mean droplet diameter lower than 200 nm cannot
be prepared .
4.Microfluidization:
Microfluidization is a patented mixing technology,
which makes use of a device called microfluidizer.
This device uses a high-pressure positive
displacement pump (500-20000 psi), which forces
the product through the interaction
chamber,consisting of small channels called
"microchannels." The product flows through the
microchannels on to an impingement area resulting
in very fine particles of submicron range. The two
solutions (aqueous phase and oily phase) are
combined together and processed in an inline
homogenizer to yield a coarse emulsion. The
coarse emulsion is into a microfluidizer where it is
further processed to obtain a stable nanoemulsion.
The coarse emulsion is passed through the
interaction chamber of the microfluidizer
repeatedly until desired particle size is obtained.
The bulk emulsion is then filtered through a filter
under nitrogen to remove large droplets resulting
in a uniform nanoemulsion.
Production With High-Amplitude Ultrasound
High-amplitude ultrasound is a viable alternative to
high-pressure homogenization. Intense shear
forces necessary for the nanoemulsification are
generated by ultrasonic cavitation, which produces
violently and asymmetrically imploding vacuum
bubbles and causes micro-jets that disperse and
break up particles down to the nanometer scale.
Known for many decades, this effect has been
extensively studied and successfully used in small-
scale production of pharmaceutical nanoemulsions
and liposomes. However, prior to the introduction
of Barbell Horn Ultrasonic Technology (BHUT),
ultrasonic liquid processors could not effectively
compete with high-pressure homogenizers in this
market because they were not able to generate
sufficiently high-amplitude (70 - 120 microns)
ultrasonic vibrations on the industrial scale.
Conventional high-power ultrasonic technology
inherently forces all processes to run either at a
small scale and high amplitude or a large scale and
low amplitude, not allowing for the possibility of
implementing high amplitudes on industrial scale.
Thus, despite its potential, the ultrasonic method
has mainly been restricted to laboratory
investigations.
Ultrasonic Technology:
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
Available online on www.ijprd.com
141
Industrial Sonomechanics, LLC, (ISM) has
successfully overcome the aforementioned
limitation by developing BHUT, which permits
constructing industrial ultrasonic systems able to
operate at extremely high ultrasonic amplitudes
(up to about 200 microns). The output tip areas of
the incorporated Barbell horns and the resulting
productivity rates of the systems are more than 10
times higher than those of any conventional
ultrasonic device operating at high amplitudes.
ISM's Barbell horn-based high-amplitude industrial
ultrasonic processors can be used for the
commercial-scale production of the highest-quality
nanoemulsions and liposomes, while offering many
advantages over high-pressure homogenizers.
These include significantly lower equipment costs,
smaller number of wetted parts (easier cleaning,
less wear and simpler servicing), no need to use a
separate rotor-stator high-shear mixer to prepare a
preliminary emulsion, as well as a much more
practicable aseptic processing. In addition, it is
much easier to create an ultrasonic system design
that eliminates the need for multiple passes of the
liquid through the system, which has not been
possible with any high-pressure homogenizer.
ISM offers directly scalable bench-top and
industrial ultrasonic processors for the
manufacture of high-quality pharmaceutical
nanoemulsions and liposomes. Our patented
ultrasonic devices utilize high-gain Barbell horns,
which make it possible to reproduce any high-
amplitude laboratory-optimized process in a
commercial production setting. These flow-through
processors provide extremely high ultrasonic
amplitudes and very uniform exposure patterns,
ensuring that all treated liquid is exposed to
tremendous ultrasonic cavitation-induced shear
forces and that no part of the liquid is able to
bypass the active cavitation zone in the reactor.
Each ISMs industrial ultrasonic processor
incorporates a calibrated amplitude sensor and is
able to display and record ultrasonic amplitudes in
microns peak to peak during operation.
Characterization of nanoparticles
Nanoemulsions are not thermodynamically stable,
because of that their characteristics will depend on
preparation method. Here some parameters are
discussed which should be analyzed at the time of
preparation of nanoemulsion .
(i) Phase behaviour study: This study is a
characterization and optimization of ingredients
(surfactant, oil phase and aqueous phase).
Generally the study is necessary in case of
nanoemulsion formulation prepared by phase
inversion temperature method and self
emulsification method in order to determine the
phase of nanoemulsion and dispersibility. Study is
done by placing the different ingredients of
nanoemulsion by varying the concentration in glass
ampules and thoroughly homogenized at a certain
temperature for a time until equilibrium.
Anisotropic phase can be identified by polarized
light.
(ii) Particle Size Analysis: Formulated
nanoemulsion should be analyzed for their
hydrodynamic particle size and particle size
distribution. Generally in case of nanoemulsion
dynamic light scattering (DLS) method are used for
the measurement of particles and further particle
size distribution.
ISMs Ultrasonic Processor
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
Available online on www.ijprd.com
142
(iii) Surface charge measurement: Surface zeta
potential of nanoemulsion droplets will be
measured with the help of mini electrode to
predict the surface properties of nanoemulsion.
(iv) Transmission Electron Microscopy (TEM): This
method is used to observe the morphology in the
nanoemulsion.
(v) Drug content: This method is used to determine
the amount of drug contained in the formulation.
Various methods (especially Western Blot method)
are used in this order.
(vi) Viscosity: Viscosity will be measured to ensure
the better delivery of the formulation.
Stability of Nanoemulsions :
Stability of a dosage form refers to the chemical
and physical integrity of the dosage unit and when
appropriate, the ability of the dosage unit to
maintain protection against microbiological
contamination . Stability of drug product is one of
the problems associated with the development of
emulsions, microemulsions and nanoemulsions.
Nanoemulsions have been known to enhance the
physical as well as chemical stability of drugs .
Stability studies are performed on
nanoemulsions by storing them at refrigerator and
room temperatures over a number of months. The
viscosity, refractive index and droplet size are
determined during this period of storage.
Insignificant changes in these parameters indicate
formulation stability. Accelerated stability studies
can also performed. In this instance, nanoemulsion
formulation are kept at accelerated temperatures
and samples withdrawn at regular intervals and
analyzed for drug content by stability indicating
HPLC methods . The amount of drug degraded and
remaining in nanoemulsion formulation is
determined at each time interval.
Morphology of Nanoemulsions
The morphology of nanoemulsions can be
determined by transmission electron microscopy
(TEM) and scanning electron microscopy (SEM).
SEM gives a three-dimensional image of the
globules . The samples are examined at suitable
accelerating voltage, usually 20 kV, at different
magnifications. A good analysis of surface
morphology of disperse phase in the formulation is
obtained through SEM. Image analysis software,
(e.g., Leica Im- aging systems, Cambridge, UK), may
be employed to obtain an automatic analysis result
of the shape and sur- face morphology .
ApplicationsOfNanoemulsions:
Parenteral Delivery:
Parenteral administration (especially via the
intravenous route) of drugs with limited solubility is
a major problem in industry because of the
extremely low amount of drug actually delivered to
a targeted site. Nanoemulsion formulations have
distinct advantages over macroemulsion systems
when delivered parenterally because of the fine
particle size. Nanoemulsion is cleared more slowly
than the coarse particle emulsion and , therefore,
have a longer residence time in the body. Both
O/W and W/O nanoemulsions can be used for
parenteral delivery. The literature contains the
details of the many nanoemulsion systems, few of
these can be used for the parenteral delivery
because the toxicity of the surfactant and
parenteral use. An alternative approach was taken
by Von Corsewant and Thoren in which C3-C4
alcohols were replaced with parenterally
acceptable co-surfactants, polyethylene glycol
(400) / polyethylene glycol (660) 12-
hydroxystearate / ethanol, while maintaining a
flexible surfactant film and spontaneous curvature
near zero to obtain and almost balanced middle
phase nanoemulsion. The middle phase structure
was preferred in this application, because it has
been able to incorporate large volumes of oil and
water with a minimal concentration of surfactant.
Oral Delivery:
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
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143
Nanoemulsion formulations offer the several
benefits over conventional oral formulation for oral
administration including increased absorption,
improved clinical potency and decreased drug
toxicity. Therefore, Nanoemulsion have been
reported to be ideal delivery of drugs such as
steroids, hormones, diuretic and antibiotics.
Pharmaceutical drugs of peptides and proteins are
highly potent and specific in their physiological
functions. However, most are difficult to
administer orally. With on oral bioavailability in
conventional (i.e. non-Nanoemulsion based)
formulation of less than 10%, they are usually not
therapeutically active by oral administration.
Because of their low oral bioavailability, most
protein drugs are only available as parenteral
formulations. However, peptide drugs have an
extremely short biological half life when
administered parenterally, so require multiple
dosing. A Nanoemulsion formulation of
cyclosporine, named Neoral has been introduced
to replace Sandimmune, a crude oil-in-water
emulsion of cyclosporine formulation. Neoral is
formulated with a finer dispersion, giving it a more
rapid and predictable absorption and less inter and
intra patient variability.
Topical Delivery:
Nanoemulsion formulation provides a rapid
penetration of active ingredients through skin due
to the large surface area of droplets. Even
sometimes it is found that nanoemulsion penetrate
easily through rough skin. This property of
nanoemulsion minimizes the additional utilization
of special penetration enhancer which is re-
sponsible for incompatibility of formulation.
Topical administration of drugs can have
advantages over other methods for several
reasons, one of which is the avoidance of hepatic
first pass metabolism of the drug and related
toxicity effects. Another is the direct delivery and
targetability of the drug to affected area of the skin
or eyes. Both O/W and W/O Nanoemulsions have
been evaluated in a hairless mouse model for the
delivery of prostaglandin E1. The Nanoemulsions
were based on oleic acid or Gelucire 44/14 as the
oil phase and were stabilized by a mixture of
Labrasol (C8 and C10 polyglycolysed glycerides)
and Plurol Oleique CC 497 as surfactant. Although
enhanced delivery rates were observed in the case
of the O/W Nanoemulsion, the authors concluded
that the penetration rates were inadequate for
practical use from either system. The use of
lecithin/IPP/water Nanoemulsion for the
transdermal transport of indomethacin and
diclofenac has also been reported. Fourier
transform infra red (FTIR) spectroscopy and
differential scanning calorimetry (DSC) showed the
IPP organogel had disrupted the lipid organisation
in human stratum corneum after a 1 day
incubation. The transdermal delivery of the
hydrophilic drug diphenhydramine hydrochloride
from a W/O Nanoemulsion into excised human skin
have also been investigated. The formulation was
based on combinations of Tween 80 and Span 20
with IPM. However two additional formulations
were tested containing cholesterol and oleic acid,
respectively. Cholesterol increased drug
penetration whereas oleic acid had no measurable
effect, but the authors clearly demonstrated that
penetration characteristics can be modulated by
compositional selection.
Ocular and Pulmonary Delivery:
For the treatment of eye diseases, drugs are
essentially delivered topically. O/W Nanoemulsions
have been investigated for ocular administration,
to dissolve poorly soluble drugs, to increase
absorption and to attain prolong release profile.
The Nanoemulsions containing pilocarpine were
formulated using lecithin, propylene glycol and PEG
200 as co-surfactant and IPM as the oil phase. The
formulations were of low viscosity with a refractive
index lending to ophthalmologic applications. The
formation of a water-in-HFA propellent
Nanoemulsion stabilized by fluorocarbon non-ionic
surfactant and intended for pulmonary delivery has
been described.
Nanoemulsions in Biotechnology:
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
Available online on www.ijprd.com
144
Many enzymatic and biocatalytic reactions are
conducted in pure organic or aqua-organic media.
Biphasic media are also used for these types of
reactions. The use of pure apolar media causes the
denaturation of biocatalysts. The use of water-
proof media is relatively advantageous. Enzymes in
low water content display and have
Increased solubility in non-polar reactants.
Possibility of shifting thermodynamic
equilibria in favour of condensations.
Improvement of thermal stability of the
enzymes, enabling reactions to be carried
out at higher temperatures.
Many enzymes, including lipases, esterases,
dehydrogenases and oxidases often function in the
cells in microenvironments that are hydrophobic in
nature. In biological systems many enzymes
operate at the interface between hydrophobic and
hydrophilic domains and these usually interfaces
are stabilized by polar lipids and other natural
amphiphiles. Enzymatic catalysis in Nanoemulsions
has been used for a variety of reactions, such as
synthesis of esters, peptides and sugar acetals
transesterification; various hydrolysis reactions and
steroid transformation. The most widely used class
of enzymes in microemulsion-based reactions is of
lipase.
Nanoemulsions in vaccine development:
Nanoemulsions can be used as a mucosal vaccine
adjuvant. Nasal spray nanoemulsion vaccine fuses
with antigen and is then sprayed into a nostril.
Nanoemulsion droplets with antigen penetrate the
nasal mucosa. Diagram of nanoemulsion droplet
with antigen in its interface. Blue dots are antigen
present in emulsion. Antigen delivery by
nanoemulsion into nasal submucosa where fusion
with dendritic cells delivers the antigen to the
immune system. Dendritic cells can then transport
the antigen to other parts of the body to trigger the
desired immune response.
Antimicrobialnanoemulsions:
Antimicrobial NEs are oil-in-water droplets that
range from 200 to 600 nm. They are composed of
oil and water and are stabilized by surfactants and
alcohol. The NE has a broad-spectrum activity
against bacteria (e.g.E.coil, salmonella, S. aureus),
enveloped viruses (e.g. HIV, Herpes simplex), fungi
(e.g. Candida, Dermatophytes), and spores (e.g.
anthrax). The NE particles are thermodynamically
driven to fuse with lipid-containing organisms.
This fusion is enhanced by the electrostatic
attraction between the cationic charge of the
emulsion and the anionic charge on the pathogen.
When enough nanoparticles fuse with the
pathogens, they release part of the energy trapped
within the emulsion. Both the active ingredient and
the energy released destabilize the pathogen lipid
membrane, resulting in cell lysis and death. In the
case of spores, additional germination enhancers
are incorporated into the emulsion. Once initiation
of germination takes place, the germinating spores
become susceptible to the antimicrobial action of
the NE. A unique aspect of the NEs is their selective
toxicity to microbes at concentrations that are non-
irritating to skin or mucous membrane. The safety
margin of the NE is due to the low level of
detergent in each droplet, yet when acting in
concert, these droplets have sufficient energy and
surfactant to destabilize the targeted microbes
without damaging healthy cells. As a result, the NE
can achieve a level of topical antimicrobial activity
that has only been previously achieved by systemic
antibiotics.
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
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145
Nanoemulsions as a mucosal vaccines .:
Nanoemulsions are being used to deliver either
recombinant proteins or inactivated organisms to a
mucosal surface to produce an immune response.
The first applications, an influenza vaccine and an
HIV vaccine, can proceed to clinical trials. The
Nanoemulsions causes proteins applied to the
mucosal surface to be adjuvanted and it facilitates
uptake by antigen-presenting cells. This results in a
significant systemic and mucosal immune response
that involves the production of specific IgG and IgA
antibody as well as cellular immunity. Initial work
in influenza has demonstrated that animals can be
protected against influenza after just a single
mucosal exposure to the virus mixed with the
emulsion. Research has also demonstrated that
animals exposed to recombinant gp120 in NE on
their nasal mucosa develop significant responses to
HIV, thus providing a basis to examine the use of
this material as an HIV vaccine. Additional research
is ongoing to complete the proof of concept in
animal trials for other vaccines including Hepatitis
B and anthrax A novel technique for vaccinating
against a variety of infectious diseases-using an oil-
based emulsion placed in the nose, rather than
needles-has proved able to produce a strong
immune response against smallpox and HIV in two
new studies.
Nanoemulsion as non-toxic disinfectant cleaner :
A breakthrough nontoxic disinfectant cleaner for
use in commercial markets that include healthcare,
hospitality, travel, food processing, and military
applications has been developed by EnviroSystems,
Inc. that kills tuberculosis and a wide spectrum of
viruses, bacteria and fungi in 5-10 min without any
of the hazards posed by other categories of
disinfectants. The product needs no warning labels.
It does not irritate eyes and can be absorbed
through the skin, inhaled, or swallowed without
harmful effects. The disinfectant formulation is
made up of nanospheres of oil droplets #106 mm
that are suspended in water to create a NE
requiring only miniscule amounts of the active
ingredient, PCMX (parachlorometaxylenol). The
nanospheres carry surface charges that efficiently
penetrate the surface charges on microorganisms'
membranes much like breaking through an electric
fence. Rather than "drowning" cells, the
formulation allows PCMX to target and penetrate
cell walls. As a result, PCMX is effective at
concentration levels 1-2 orders of magnitude lower
than those of other disinfectants; hence, there are
no toxic effects on people, animals, or the
environment. Other microbial disinfectants require
large doses of their respective active ingredients to
surround pathogen cell walls, which cause them to
disintegrate, fundamentally "drowning" them in
the disinfectant solution. The formulation is a
broad-spectrum disinfectant cleaner that can be
applied to any hard surface, including equipment,
counters, walls, fixtures, and floors. One product
can now take the place of many reducing product
inventories and saving valuable storage space.
Chemical disposal costs can be eliminated, and
disinfection and cleaning costs can be reduced. It is
marketed as a EcoTru (EnviroSystems, Inc.)
Nanoemulsions in cell culture technology
Cell cultures are used for in vitro assays or to
produce biological compounds, such as antibodies
or recombinant proteins. To optimize cell growth,
the culture medium can be supplemented with a
number of defined molecules or with blood serum.
Up to now, it has been very difficult to supplement
the media with oil-soluble substances that are
available to the cells, and only small amounts of
these lipophilic compounds could be absorbed by
the cells. NEs are a new method for the delivery of
oil-soluble substances to mammalian cell cultures.
The delivery system is based on a NE, which is
stabilized by phospholipids. These NEs are
transparent and can be passed through 0.1 mm
filters for sterilization. NE droplets are easily taken
up by the cells. The encapsulated oil-soluble
substances therefore have a high bioavailability to
cells in culture. The advantages of using NEs in cell
culture technology are better uptake of oil-soluble
supplements in cell cultures; improve growth and
vitality of cultured cells, and allowance of toxicity
studies of oil-soluble drugs in cell cultures.
International Journal of Pharmaceutical Research & Development ISSN: 0974 9446
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146
Nanoemulsion in cancer therapy and in targeted
drug delivery :
It is also reported that nanoemulsion may be used
for the target delivery of active ingredient
especially in cancer therapy.The effects of the
formulation and particle composition of gadolinium
(Gd)-containing lipid NE (Gd-nanoLE) on the
biodistribution of Gd after its intravenous (IV)
injection in D1-179 melanoma-bearing hamsters
were evaluated for its application in cancer
neutron-capture therapy. Biodistribution data
revealed that Brij 700 and HCO-60 prolonged the
retention of Gd in the blood and enhanced its
accumulation in tumors. Among the core
components employed, soybean oil yielded the
highest Gd concentration in the blood and tumor,
and the lowest in the liver and spleen. When each
Gd-nanoLE was IV injected once or twice at a 24-h
interval, the Gd concentration in the tumor
correlated well with the total dose of Gd, and it
reached a maximum of a 189 mg/g wet tumor. This
maximum Gd level was greater than the limit
required for significantly suppressing tumor growth
in neutron-capture therapy. In order to achieve
penetration of Paclitaxel (PCL) into deeper skin
layers while minimizing the systemic escape, a NE
(NE) was formulated and its in
vivo pharmacokinetic performance was evaluated.
Further, the same formulation was explored for
peroral bioavailability enhancement of PCL. Upon
dermal application, the drug was predominantly
localized in deeper skin layers, with minimal
systemic escape. This has amounted to an absolute
bioavailability of 70.62%. Inhibition of P-
glycoprotein efflux by D-tocopheryl
polyethyleneglycol 1000 succinate and labrasol
would have contributed to the enhanced peroral
bioavailability of PCL. This investigation provides
direct evidence on the localization of high-
molecular-weight, lipophilic drug, PCL, in dermis.
Further, the NE formulation has enhanced the
peroral bioavailability significantly to more than
70%. The developed NE formulation was safe and
effective for both.
Camptothecin is a topoisomerase I inhibitor that
acts against a broad spectrum of cancers. However,
its clinical application is limited by its insolubility,
instability, and toxicity. The aim of the present
study was to develop acoustically active NEs for
camptothecin encapsulation to circumvent these
delivery problems. The NEs were prepared using
liquid perfluorocarbons and coconut oil as the
cores of the inner phase. These NEs were stabilized
by phospholipids and/or Pluronic F68 (PF68). The
NEs were prepared at high drug loading of
approximately 100% with a mean droplet diameter
of 220-420 nm. Camptothecin in these systems
showed retarded drug release. Camptothecin in
NEs with a lower oil concentration exhibited
cytotoxicity against melanomas and ovarian cancer
cells. Confocal laser scanning microscopy
confirmed NE uptake into cells. Using a 1 MHz
ultrasound, an increased release of camptothecin
from the system with lower oil concentration could
be established, illustrating a drug-targeting effect.
The advantages of formulating various lipophilic
anti-cancer drugs in submicron O/W emulsion are
obvious. The oil phase of the emulsion systems can
act as a solubilizer for the lipophilic compound.
Therefore, solubility of lipophilic drugs can be
significantly enhanced in an emulsion system,
leading to smaller administration volumes
compared to an aqueous solution. In addition,
because lipophilic drugs are incorporated within
the innermost oil phase, they are sequestered from
direct contact with body fluids and tissues. Lipid
emulsions can minimize the pain associated with
intravenously administered drugs by exposing the
tissues to lower concentrations of the drug or by
avoiding a tissue-irritating vehicle. This has been
demonstrated with propofol, diazepam,
methohexital, clarithromycin, and etomidate.
Another study reported the formulation of filter
sterilizable emulsion formulation of paclitaxel using
-tocopherol as the oil phase and -
tocopherylpolyethyleneglycol-1000 succinate
(TGPS) and poloxamer 407 as emulsifiers. The
formulation exhibited better efficacy and was more
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147
tolerable when studied in B16 melanoma tumor
model in mice.
Emulsion formulations also show promise in cancer
chemotherapy as vehicles for prolonging the drug
release after intramuscular and intratumoral
injection (W/O systems) and as a means of
enhancing the transport of anti-cancer drugs via
the lymphatic system.
The perfluorochemical Nanoemulsions (PFCE) have
opened interesting opportunities in cancer
therapy. It is suggested that fluorocarbon
emulsions might find a role in photodynamic
therapy, both as carriers for sensitizing dyes and to
maintain tissue oxygenation in hypoxic regions of
solid tumors. The high solubility of oxygen in
fluorocarbon emulsions maintains solution oxygen
tension, optimizing photo-oxidative damage. The
hydrophobic anti-cancer drugs can be delivered to
the tumor mass by dissolving them in a
hydrophobic core of the emulsion. Furthermore,
PFCE can be used as an adjuvant to radiation
therapy and/or chemotherapy in the treatment of
solid tumors.
The preclinical studies have shown very positive
effects with single dose and fractionated radiation
in several rodent solid tumor models. Many widely
used anticancer drugs, including anti-tumor
alkylating agents and doxorubicin, have shown
improved response by PFCE coadministration. Also,
local application of toxic doses of PFCEs resulted in
the necrosis of cancer cells. This is especially
promising in the treatment of cancers of the head
and neck regions that are currently difficult to
treat.
Nanoemulsion in the treatment of various other
disease conditions:
Pharmos' (US-based company) has developed the
nanoemulsion topical diclofenac cream as a
potential treatment for osteoarthritis (OA) pain.
Topical diclofenac is also being considered as
treatment for soft tissue injuries, sprains, and
strains. It is estimated that 20% of OA patients are
not receiving treatment, mainly due to
gastrointestinal side effects of oral NSAIDs and
cardiovascular risk of COX-2 inhibitors. A topical
NSAID offering adequate pain relief targeted to the
site of injury with an improved safety profile could
become a treatment alternative for these patients.
One of the unique characteristics of the
Nanoemulsion technology is the relatively high
percentage of total particle volume occupied by
the internal hydrophobic oil core of the droplets.
This provides high solubilization capacity for
lipophilic compounds compared to other lipoidal
vehicles such as liposomes. Viscosity-imparting
agents are used for nanoemulsion thickening to
produce creams with the desired semisolid
consistency for application to the skin. The skin
penetrative properties of the solvent-free NE
delivery technology and its low irritancy make this
novel topical nanovehicle a promising candidate for
effective transcutaneous delivery of lipophilic
drugs. A topical application of the nanotechnology
has already demonstrated excellent targeted
delivery of lipophilic drugs to muscle and joints in
animal models. Preclinical data using a paw edema
animal model showed enhanced anti-inflammatory
activity with NSAIDs encapsulated in nanoemulsion
creams compared to commercial formulations.
Pharmacokinetic studies using nanoemulsion
topical creams containing radiolabeled diclofenac
and ketoprofen were performed to assess drug
penetration through skin and to determine local
tissue (muscle and joint) and plasma levels of drugs
following topical administration. Compared to oral
administration, diclofenac and ketoprofen
administered via nanoemulsion topical creams
demonstrated 4- to 6-fold lower drug
concentration in plasma, 60-to 80-fold more drug
in muscle tissue, and about 9-fold more drug in
jointsThe NE technology consists of spheric oily
droplets (in the range of 100-200 nm) uniformly
dispersed in an aqueous medium. The emulsion
droplet size reduction is essential to generate drug
formulations with high stability. The NE technology
has been successfully applied in the formulation of
ophthalmic preparations showing improved drug
delivery and reduced ocular irritation in humans in
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148
Phase I/II clinical studies.
Primaquine (PQ) is one of the most widely used
antimalarial and is the only available drug till date
to combat relapsing form of malaria especially in
case of Plasmodium vivax and Plasmodium ovale.
Primaquine acts specifically on the pre-erythrocytic
schizonts that are concentrated predominantly in
the liver and causes relapse after multiplication.
However, application of PQ in higher doses is
limited by severe tissue toxicity including
hematological and GI-related side effects that are
needed to be minimized. Lipid NE has been widely
explored for parenteral delivery of drugs.
Primaquine when incorporated into oral lipid NE
having a particle size in the range of 10-200 nm
showed effective antimalarial activity
against Plasmodium bergheii infection in Swiss
albino mice at a 25% lower dose level as compared
to conventional oral dose. Lipid NE of primaquine
exhibited improved oral bioavailability and was
taken up preferentially by the liver with drug
concentration higher at least by 45% as compared
to the plain drug.
Nanoemulsion formulations for improved oral
delivery of poorly soluble drugs :
NE formulations were developed to enhance oral
bioavailability of hydrophobic drugs. Paclitaxel was
selected as a model hydrophobic drug. The oil-in-
water (o/w) Nanoemulsions were made with pine
nut oil as the internal oil phase, egg lecithin as the
primary emulsifier, and water as the external
phase.
Stearylamine and deoxycholic acid were used to
impart positive and negative charge to the
emulsions,respectively.
Coenzyme Q10 (CoQ10), also known as
ubiquinone, is used for energy production within
cells and acts as an anti-oxidant. Since CoQ10 is
highly lipophilic, the topical and oral bioavailability
is very low. Several attempts have been made to
improve absorption. Latest technical developments
reveal that encapsulation of CoQ10 in NEs results
in a significantly enhanced bioavailability. The
application of CoQ10 has been further improved by
the development of novel CoQ10 double NEs
containing tocopherol and CoQ10 in individual
nanodroplets. In addition, the CoQ10
concentration in these NEs could be increased by
the development of a supersaturated CoQ10 NE.
Nanoemulsions as a vehicle for transdermal
delivery:
From in vitro and in vivo data, it was concluded
that the developed NEs have great potential for
transdermal drug delivery of aceclofenac. The NEs
of the system containing ketoprofen evidenced a
high degree of stability. Ketoprofen-loaded NEs
enhanced the in vitro permeation rate through
mouse skins as compared to the control.
The study was developed to evaluate the potential
of NEs for increasing the solubility and the in
vitro transdermal delivery of carvedilol. The
prepared NEs were subjected to physical stability
tests. Transdermal permeation of carvedilol
through rat abdominal skin was determined with
the Keshary-Chien diffusion cell. Significant
increase (P < 0.05) in the steady state flux (Jss) and
permeability coefficient (Kp) was observed in NE
formulations as compared to control or drug-
loaded neat components. The irritation studies
suggested that the optimized NE was a non-irritant
transdermal delivery system.
Celecoxib, a selective cyclo-oxygenase-2 inhibitor,
has been recommended orally for the treatment of
arthritis and osteoarthritis. Long-term oral
administration of celecoxib produces serious
gastrointestinal side effects. Skin permeation
mechanism of celecoxib from NE was evaluated by
FTIR spectral analysis, DSC thermogram, activation
energy measurement, and histopathological
examination. The optimized NE was subjected to
pharmacokinetic (bioavailability) studies on Wistar
male rats. Photomicrograph of a skin sample
showed the disruption of lipid bilayers as distinct
voids and empty spaces were visible in the
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149
epidermal region. Results of skin permeation
mechanism and pharmacokinetic studies indicated
that the NEs can be successfully used as potential
vehicles for enhancement of skin permeation and
bioavailability of poorly soluble drugs.
Solid self-nanoemulsifying delivery systems as a
platform technology for formulation of poorly
soluble drugs :
New drug discovery programs produce molecules
with poor physico-chemical properties, making
delivery of these molecules at the right proportion
into the body, a big challenge to the
formulationscientist. The various options available
to overcome the hurdle include solvent
precipitation, micronisation or nanonization using
high-pressure homogenization or jet milling, salt
formation, use of microspheres, solid dispersions,
cogrinding, complexation, and many others. Self-
nanoemulsifying systems (SNES) form one of the
most popular and commercially viable approaches
for delivery of poorly soluble drugs exhibiting
dissolution rate limited absorption, especially those
belonging to the Biopharmaceutics Classification
System II/IV. SNES are essentially an isotropic blend
of oils, surfactants, and/or cosolvents that emulsify
spontaneously to produce oil in water NE when
introduced into aqueous phase under gentle
agitation. Conventional SNES consist of liquid forms
filled in hard or soft gelatin capsules, which are
least preferred due to leaching and leakage
phenomenon, interaction with capsule shell
components, handling difficulties, machinability,
and stability problems. Solidification of these liquid
systems to yield solid self-nanoemulsifying systems
(SSNES) offer a possible solution to the mentioned
complications, and that is why these systems have
attracted wide attention.
Use of nanoemulsions in cosmetics:
NEs have recently become increasingly important
as potential vehicles for the controlled delivery of
cosmetics and for the optimized dispersion of
active ingredients in particular skin layers. Due to
their lipophilic interior, NEs are more suitable for
the transport of lipophilic compounds than
liposomes. Similar to liposomes, they support the
skin penetration of active ingredients and thus
increase their concentration in the skin. Another
advantage is the small-sized droplet with its high
surface area allowing effective transport of the
active to the skin. Furthermore, NEs gain increasing
interest due to their own bioactive effects. This
may reduce the trans-epidermal water loss (TEWL),
indicating that the barrier function of the skin is
strengthened. NEs are acceptable in cosmetics
because there are no inherent creaming,
sedimentation, flocculation, or coalescence that
are observed with macroemulsions. The
incorporation of potentially irritating surfactants
can often be avoided by using high-energy
equipment during manufacturing.
NanoGel technology provides a simple process and
system to create submicron emulsions from an
easy-to-use, oil-in-water concentrate. The formula
is particularly suited to minimizing transepidermal
water loss, enhanced skin production, and
penetration of active ingredient. These
characteristics suggest that it would be particularly
useful for sun care products as well as moisturizing
and anti-aging creams-particular areas where
nanotechnology is already being incorporated into
a host of products currently on the market.
Likewise, it is also highlighted that it helps to give
skin care formulations a good skin feel, an
increasingly important characteristic for
formulators.
NEs have attracted considerable attention in recent
years for application in personal care products as
potential vehicles for the controlled delivery of
cosmetics and the optimized dispersion of active
ingredients in particular skin layers.
Evaluation of Nanoemulsions:
In Vitro Skin Permeation Studies (for transdermal
drug delivery system):
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Franz diffusion cell is used to obtain the drug
release profile of the nanoemulsion formulation in
the case of formulations for transdermal
application. The extent or depth of skin
penetration by the released content can be
visualized by confocal scanning laser microscopy. In
vitro drug release can be determined by dispersing
an amount of the preparation in the donor
compartment of a Franz cell having a membrane as
barrier and monitoring the appearance of the
encapsulated drug in the reception medium,
usually PBS (pH 7.4) and stirring on a magnetic
stirrer at 100 rpm at 37C 1C. Samples (1 ml) of
the dispersion are withdrawn from the medium
and replaced with an equivalent amount of the
medium at definite intervals. The withdrawn
sample is then filtered using a 0.22 - 50 m filter
(e.g., Millipore, USA) and the drug released then
analyzed using UV-visible spectroscopy at
wavelength of peak absorption of the drug . An
alternative and popular method of ex-vivo release
study is performed using diffusion cell. The skin is
cut from the ear or abdomen and underlying
cartilage and fats care- fully removed. Appropriate
size of skin is cut and placed on the diffusion cell
which had earlier been filled with receptor
solution. Samples of the vesicular preparation are
then applied on the dorsal surface of the skin and
the instrument started. At intervals, up to 24 h,
samples are withdrawn from the receptor medium
and replaced with equal amounts of the medium
and the withdrawn samples analyzed for the drug
permeated using HPLC or UV spectroscopy. Semi-
permeable membrane such as regenerated
cellulose could be used in place of skin for in vitro
release studies. The flux J, of the drug across the
skin or membrane is calculated from the formula:
J = D dc/dx (2)
where D is the diffusion coefficient and is a
function of the size, shape and flexibility of the
diffusing molecule as well as the membrane
resistance, c is the concentration of the diffusing
species, x is the spatial coordinate .
In vivo release study otherwise referred to as
dermatopharmacokinetics, is carried out by
applying or admin- istering the preparation to
whole live animal. Blood samples are then
withdrawn at intervals, centrifuged and the plasma
analyzed for the drug content using HPLC. Results
obtained from in vitro and in vivo studies are
extrapolated to reflect bioavailability of the drug
formulation.
ADVANTAGES OF NANOEMULSIONS OVER OTHER
DOSAGE FORMS
Increase the rate of absorption.
Eliminates variability in absorption.
Helps solublize lipophilic drug.
Provides aqueous dosage form for water
insoluble drugs.
Increases bioavailability.
Various routes like tropical, oral and
intravenous can be used to deliver the product.
Rapid and efficient penetration of the drug
moiety.
Helpful in taste masking.
Provides protection from hydrolysis and
oxidation as drug in oil phase in O/W
Nanoemulsion is not exposed to attack by
water and air.
Liquid dosage form increases patient
compliance.
Less amount of energy requirement.
Nanoemulsion has a transparent and fluidy
property which improves the formulation
patient compliance and safe for administration
due to the absence of any thickening agent and
colloidal particles.
Nanoemulsions are thermodynamically stable
system and the stability allows self-
emulsification of the system .
Nanoemulsion formulation required low
amount of surfactant compared to
microemulsion. For example about 20- 25 %
surfactant is required for the preparation of
microemulsion but 5-10 % surfactant is suffi-
cient in case of nanoemulsion.
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Limitations of nanoemulsions:
Even though nanoemulsions provide great
advantages as a delivery system, but sometimes
the re duced size of droplets are responsible for
the limited use of nanoemulsion formulation. Some
limitations of nanoemulsions are as follows :
The manufacturing process of nanoemulsion
formulation is expensive, because size
reduction of droplets is very difficult as it
required a special kind of instruments and
process methods. For example, homogenizer
arrangement, microfluidization
&ultrasonification require high financial
support.
Nanoemulsion stability creates a big problem
during the storage of formulation for the longer
time period. Ostwald ripening is the main factor
associated with unacceptability of
nanoemulsion formulations. This is due to the
high rate of curvature of small droplet show
greater solubility as compared to large drop
with a low radius of curvature.
Less availability of surfactant and co-surfactant
required for the manufacturing of
nanoemulsion is another factor which marks as
a limitation to nanoemulsion manufacturing.
Limited solubilizing capacity for high-melting
substances.
CONCLUSION:
Nanoemulsions have now-a-days become an
answer for the questions regarding targeted
delivery . Because of their submicron size , they can
be easily targeted . Moreover, the possibility of
surface functionalization with a targeting moiety
has opened new avenues for targeted delivery of
drugs, genes, photosensitizers& other molecules of
tumer area. So,nanoemulsions can set a better
mark for targeted drug delivery system
.
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