5. Formulation and Development of Microemulsion...

5. Formulation and Development of Microemulsion and SMEDDS


Akshay R. Koli 139

Contents

5 Formulation and Development of Microemulsion and SMEDDS…………….…142

5.1 Formulation techniques for Microemulsion ......................................... 142

5.1.1 Phase titration method (Water titration method): ........................ 142

5.1.2 Phase inversion method: .............................................................. 143

5.1.3 Method developed by Boycott and Schulman:.............................. 144

5.2 Selection of excipients used for microemulsion and SMEDDS .............. 145

5.2.1 Drug solubility determination in oils, surfactants & co-surfactants 145

5.2.2 Drug – selected surfactants compatibility study:........................... 150

5.3 Optimization of surfactant: co-surfactant ratio by pseudo-ternary

phase diagram .............................................................................. 152

5.3.1 Microemulsion System: ................................................................ 153

5.3.2 SMEDDS ........................................................................................ 156

5.4 Effect of Drug loading on the phase diagrams of the selected systems 165

5.4.1 Felodipine Microemulsion: ........................................................... 165

5.4.2 Valsartan SMEDDS ........................................................................ 167

5.5 Preparation of Drug Loaded Microemulsions and SMEDDS .................. 169

5.5.1 Felodipine Microemulsion: ........................................................... 170

5.5.2 Valsartan SMEDDS: ....................................................................... 171

5.6 References ........................................................................................... 174


Akshay R. Koli 140

List of Tables

Table 5.2.1.1: Solubility of Felodipine in excipients ........................................... 147

Table 5.2.1.2: Solubility of Valsartan in excipients ............................................ 149

Table 5.2.2.1: Drug - selected surfactant compatibility study for Felodipine ..... 151

Table 5.2.2.2: Drug - selected surfactants compatibility study for Valsartan ..... 152

Table 5.3.1.1: Water titration Reading for Phase diagram (Microemulsion System)

......................................................................................................................... 154

Table 5.3.2.1: Water titration Readings for Phase Diagram (V1) ....................... 157



Table 5.5.1.1: Compositions of Felodipine Microemulsion Systems (Batch F1 – F9)

......................................................................................................................... 170

Table 5.5.2.1: Compositions of Valsartan SMEDDS 1 (V1) ................................. 172




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List of Figures

Figure 5.1.1.1:Pseudoternary phase diagram of oil, water and surfactant

mixture showing microemulsion region ..................................... 143

Figure 5.2.1.1: Solubility of Felodipine in excipients .......................................... 148

Figure 5.2.1.2: Solubility of Valsartan in excipients ........................................... 150

Figure 5.3.1.1: Pseudo-ternary phase diagrams of Capmul MCM (oil), Tween20:

PEG 400 (S:CoS) and Water system ............................................ 155

Figure 5.3.2.1: Excipients profiles for three different systems of SMEDDS ........ 157

Figure 5.3.2.2: Pseudo-ternary phase diagrams of Capmul MCM (oil), Tween 80:

PEG 400 (S:CoS) and Water system ............................................ 158

Figure 5.3.2.3: Pseudo-ternary phase diagrams of Capmul MCM (oil), Labrasol:

Transcutol P (S:CoS) and Water system ...................................... 160


Transcutol P (S:CoS) and Water system ...................................... 161

Figure 5.4.1.1: Pseudoternary phase diagram of Capmul MCM, Tween 20 and

PEG 400 (Placebo) ...................................................................... 166

Figure 5.4.1.2: Pseudoternary phase diagram of Felodipine, Capmul MCM,

Tween 20 and PEG 400............................................................... 166

Figure 5.4.2.1: Pseudoternary phase diagram of Capmul MCM, Tween 80 and

PEG 400 (Placebo) ...................................................................... 168

Figure 5.4.2.2: Pseudoternary phase diagram of Valsartan, Capmul MCM,

Tween 80 and PEG 400............................................................... 168

Figure 5.4.2.1: Flow Chart of preparation of SMEDDS and Microemulsion ........ 169


Akshay R. Koli 142

5 Formulation and Development of Microemulsion and

SMEDDS

5.1 Formulation techniques for Microemulsion

Many researchers in various literatures have reported the formulation techniques for

microemulsion. These techniques include:-

5.1.1 Phase titration method (Water titration method):

Microemulsions are prepared by the spontaneous emulsification method (phase titration

method) and can be depicted with the help of phase diagrams. Construction of phase

diagram is a useful approach to study the complex series of interactions that can occur

when different components are mixed. Microemulsions are formed along with various

association structures (including emulsion, micelles, lamellar, hexagonal, cubic, and

various gels and oily dispersion) depending on the chemical composition and

concentration of each component. The understanding of their phase equilibria and

demarcation of the phase boundaries are essential aspects of the study. As quaternary

phase diagram (four component system) is time consuming and difficult to interpret,

pseudo ternary phase diagram is often constructed to find the different zones including

microemulsion zone, in which each corner of the diagram represents 100% of the

particular component as shown in Figure 5.1.1.1. They can be separated into w/o or o/w

microemulsion by simply considering the composition that is whether it is oil rich or

water rich. Observations should be made carefully so that the metastable systems are not

included[1]

.

In this method, at a constant ratio of S/CoS, various combinations of oil and S/CoS are

produced and the water is added drop wise. After the addition of each drop, the mixture is

stirred and examined through a polarized filter or by naked eye. The appearance

(transparency, opalescence and isotropy) is recorded after addition of each drop of

water[2]

.


Akshay R. Koli 143

Figure 5.1.1.1:Pseudoternary phase diagram of oil, water and surfactant mixture

showing microemulsion region

5.1.2 Phase inversion method:

Phase inversion of microemulsions occurs upon addition of excess of the dispersed phase

or in response to temperature. During phase inversion drastic physical changes occur

including changes in particle size that can affect drug release both in vivo and in vitro.

These methods make use of changing the spontaneous curvature of the surfactant. For

non-ionic surfactants, this can be achieved by changing the temperature of the system,

forcing a transition from an o/w microemulsion at low temperatures to a w/o

microemulsion at higher temperatures (transitional phase inversion). During cooling, the

system crosses a point of zero spontaneous curvature and minimal surface tension,

promoting the formation of finely dispersed oil droplets. This method is referred to as

phase inversion temperature (PIT) method. Instead of the temperature, other parameters

such as salt concentration or pH value may be considered as well instead of the

temperature alone.

Additionally, a transition in the spontaneous radius of curvature can be obtained by

changing the water volume fraction. By successively adding water into oil, initially water

droplets are formed in a continuous oil phase. Increasing the water volume fraction

changes the spontaneous curvature of the surfactant from initially stabilizing a w/o

microemulsion to an o/w microemulsion at the inversion locus. Short-chain surfactants

form flexible monolayers at the o/w interface resulting in a bicontinuous microemulsion

at the inversion point[1]

.


Akshay R. Koli 144

5.1.3 Method developed by Boycott and Schulman:

In this method, adding the oil, surfactant mixture to some of the aqueous phase in a

temperature controlled container with agitation makes a coarse macro emulsion as a first

step, which is then titrated with co-surfactant until clarity is obtained and then diluted

with water to give a microemulsion of the desired concentration[2]

.

The desired characteristics of microemulsions and SMEDDS are dilutability,

transparency, globule size in the range of 100 nm for enhanced absorption, zeta potential

around -10 to -30 mV for stability[3]

. The parameters which can affect these properties are

the nature and concentration of oil, surfactant and co-surfactant. The ratio of surfactant:

co-surfactant plays a very important role in successful preparation of microemulsion.

Hence these parameters were studied and optimized to obtain the desirable

microemulsion formulation. The dependent parameters were Dilutability, Percentage

transmittance, Droplet size and Zeta potential[4]

. Here water titration method was used for

preparation of microemulsion and SMEDDS because it is easy & scalable.


Akshay R. Koli 145

5.2 Selection of excipients used for microemulsion and

SMEDDS

Development of microemulsion systems for poorly water soluble drugs is critical.

Components selected for the formulation should have the ability to solubilize the drug in

high level to deliver the therapeutic dose of the drug in an encapsulated form. In general,

excipients with higher solubilizing efficiency for drug are selected for formulation

development.

5.2.1 Drug solubility determination in oils, surfactants & co-surfactants

Solubility of drugs was determined in different oils (such as capmul MCM, Capryol 90,

Capmul MCM C8, Capmul MCM C10, Captex 200P, Captex 355, Isopropyl myristate,

Soyabean oil, Castor oil), surfactants (such as Tween 20, Tween 80, Labrasol, Plurol

oleique, Cremophore EL) and co-surfactants (such as Transcutol P, PEG 400, Labrafil

1944 CS). Non-ionic surfactants were used in this study since they are known to be less

affected by pH and changes in ionic strength. Drug was added in excess amount into 2 ml

of each component in vials and stirred for 48 hrs at 25 ˚C on magnetic stirrer. The

mixture vials were then kept at 25±1.00C in an isothermal shaker for 72 h to reach

equilibrium[6, 7]

. The equilibrated samples were removed from shaker and centrifuged at

3000 rpm for 15 min to remove the excess drug, after which the concentration of drug in

supernatant was measured by UV spectrophotometric method after appropriate dilution

with methanol. Then drug solubility (mg/ml) was calculated and depicted in Table 5.2.1.1

and 5.2.1.2 for Felodipine and Valsartan respectively.

Result and Discussion

The components used in the system should have high solubilization capacity for the drug,

ensuring the solubilization of the drug in the resultant dispersion. The higher solubility of

the drug in the oil phase is important for the microemulsion and SMEDDS to maintain

the drug in solubilized form. In present study, oils namely capmul MCM, capmul MCM

C8, capmul MCM C10, captex 200P, captex 355, castor oil, isopropyl myristate and olive

oil were screened for solubilization of both drugs.


Akshay R. Koli 146

In the present study, non ionic surfactants namely tween20, tween 80, labrasol, peceol

and plurol oleique were screened as nonionic surfactants are less toxic than ionic

surfactants. Microemulsion dosage forms for oral or parenteral use based on nonionic

surfactants are likely to offer in vivo stability[8]

. Transient negative interfacial tension and

fluid interfacial film is rarely achieved by the use of single surfactant, usually

necessitating the addition of a co-surfactant. The presence of co-surfactant decreases the

bending stress of interface and allows the interfacial film sufficient flexibility to take up

different curvatures required to form microemulsion over a wide range of composition.

Thus, the co-surfactants namely PEG 400, propylene glycol and Transcutol P were

screened for the study that again are nonionic surfactants.

Since the Felodipine and Valsartan are highly lipophilic, it was presumed that keeping

them in lipophilic environment might increase their stability[9]

.

Felodipine:

The solubility of Felodipine in different oils, surfactants, co-surfactants and water was

determined (Table 5.2.1.1 and Figure 5.2.1.1). The solubility of Felodipine was found to

be highest in Capmul MCM (90±1.25 mg/ml) as compared to other oils while in water it

was 0.0191 mg/ml[10]

. This may be attributed to the polarity of the poorly water soluble

drugs that favor their solubilization in small/medium molecular volume oils such as

medium chain triglycerides or mono- or diglycerides[11]

.


Akshay R. Koli 147

Table 5.2.1.1: Solubility of Felodipine in excipients

Ingredients Solubility (mg/ml)

Oils

Capmul MCM 90 ± 1.25

Capmul MCM C8 80 ± 1.17


Captex 200P 32.25 ± 3.09

Captex 355 3.89 ± 2.36

Castor oil 8.50 ± 4.24

Olive oil 3.87 ± 2.40

Isopropyl myristate 2.78 ± 1.44

Surfactants

Tween 20 120 ± 2.52

Tween 80 100 ± 2.47

Labrasol 15 ± 1.25

Plurol oleique 10 ± 3.30

Co-surfactants

PEG 400 120 ± 3.44

Propylene glycol Insoluble


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Figure 5.2.1.1: Solubility of Felodipine in excipients

The studies have revealed that mixed mono and diglyceride like Capmul gave

microemulsion (clear or translucent liquid) and emulsion phases, whereas di- and

triglycerides exhibited an additional gel phase. Among individual mono-, di- and

triglycerides, the oil-in-water microemulsion region was found to be the largest for the

diglyceride. Dispersion of drug in aqueous media from mixtures of mono- and

diglyceride or mono- and triglyceride was superior to individual lipids[12]

. Mono-

diglyceride medium chain esters like Capmul MCM are particularly recommended for the

dissolution of difficult compounds[13]

. Hence Capmul MCM was selected as the oil

phase. The solubility of Felodipine was also very high in Tween 20 and PEG 400. Hence

these components were selected as surfactant and co-surfactant for microemulsion system

preparation.

Valsartan:

The solubility of Valsartan in different oils, surfactants, co-surfactants and water was

determined (Table 5.2.1.2 and Figure 5.2.1.2). The solubility of Valsartan was found to

0

20

40

60

80

100

120

140

Solu

bili

ty (m

g/m

l)

Excipients


Akshay R. Koli 149

be highest in Capmul MCM (110±1 mg/ml) as compared to other oils while in water it

was 0.003±0.01mg/ml. This may be attributed to the polarity of the poorly water soluble

drugs that favor their solubilization in small/medium molecular volume oils such as

medium chain triglycerides or mono- or diglycerides[11]

.

Table 5.2.1.2: Solubility of Valsartan in excipients

Ingredients Solubility (mg/ml)

Oils

Capmul MCM 110 ± 1.2



Captex 200 P 15 ± 3.06

Captex 355 NF 42 ± 3.5

Olive oil 8 ± 3.5

Isopropyl myristate 10 ± 1.5

Surfactants

Tween 80 60 ± 5.5

Labrasol 90± 1.2

Peceol 82± 3.00

Co-surfactants

PEG 400 10.67± 2.7

Transcutol P 12 ± 0.5


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Figure 5.2.1.2: Solubility of Valsartan in excipients

From above data, highest solubility of Valsartan was found in capmul MCM as oil. Due

to suitability of Capmul MCM as an oil phase as per previous discussion, it was selected

as oil phase. All three surfactants i.e. Tween 80, Peceol and Labrasol show comparable

solubility of Valsartan. Thus all of them were taken for further studies. The solubility of

Valsartan was almost similar in PEG 400 and Transcutol P. Thus Tween 80, peceol and

Labrasol were selected as surfactants and PEG 400 and Transcutol P as co-surfactants for

SMEDDS preparation.

5.2.2 Drug – selected surfactants compatibility study:

Physical compatibility of the water-insoluble drug with surfactants should be used in

surfactant selection procedure. Physical compatibility may include

precipitation/crystallization, phase separation and color change in the drug surfactant

solution during course study. Chemical compatibility is primarily regarded as the

chemical stability of the drug in a surfactant solution. A surfactant was considered for

further development only if it was physically and chemically compatible with drug. A

0

20

40

60

80

100

120

Solu

bili

ty (m

g/m

l)

Excipients


Akshay R. Koli 151

fixed amount (5 ml) of each of the surfactant:co-surfactant (1:1) was placed in a 10 ml

glass vial with a known amount (100 mg) of drug. The samples were stored under 25oC

for 1 month and observed for physical changes and analyzed for chemical changes[14]

.

Results and Discussion

The drug and surfactant compatibility study was designed to evaluate the effect of Tween

20 on the physical and chemical stability of Felodipine and effect of Tween 80, Peceol

and Labrasol on the physical and chemical stability of Valsartan. This study was found to

be very useful because concentrations of surfactants are usually quite high in

microemulsion formulations. As data demonstrated in Table 5.2.2.1 and 5.2.2.2, there

were no significant losses of potency (less than 10%) in any of the samples. Felodipine

did not show any signs of incompatibility with surfactant and co-surfactant mixture. The

results are as shown in Table 5.2.2.1.

Table 5.2.2.1: Drug - selected surfactant compatibility study for Felodipine

Surfactant :

Co-Surfactant

Mixture (1:1)

Precipitation Crystallization Phase

separation

Color

change

%

Recovery(1

month at

250C)

Tween 20:PEG

400

× × × × 99.0

Where, √- Presence and ×- Absence

In case of Valsartan, Peceol : PEG 400 and Labrasol : PEG 400 combinations showed

precipitation during 1 month study. Thus they were eliminated from further studies. The

remaining S:CoS combinations passed the Durg-Surfactant compatibility test. These

results showed promise for a SMEDDS formulation which could be the way to proceed

further to meet the dose requirement for Valsartan. The results are as shown in Table

5.2.2.2.


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Table 5.2.2.2: Drug - selected surfactants compatibility study for Valsartan

Surfactant:CoSurfac

tant Mixture (1:1)

Precipitati

on

Crystallizati

on

Phase

separati

on

Color

chan

ge

%

Recovery

(1 month

at 250C)

Tween 80:PEG 400 × × × × 99.3

Labrasol : Transcutol

P

× × × × 97.8

Peceol : PEG 400 √ × × × 96.1

Tween 80: Transcutol

P

× × × × 99.3

Labrasol : PEG 400 √ × × × 97.8

Where, √- Presence and ×- Absence

5.3 Optimization of surfactant: co-surfactant ratio by

pseudo-ternary phase diagram

The existence of microemulsions regions were determined using pseudo-ternary phase

diagrams. The mixture of oil and surfactant/co-surfactant at certain weight ratios were

diluted with water in a drop wise manner. Distill water was used as an aqueous phase for

the construction of phase diagrams. For construction of pseudo ternary phase diagrams,

water titration method was used because this method is easy & scalable. In this study,

microemulsions were prepared to find the area of particular component system[6, 15, 16]

.

In this method, surfactant was blended with co-surfactant in fixed weight ratios i.e. 1:1,

2:1, 3:1, and 4:1 for Felodipine Microemulsion and 3:1, 2:1 and 1:1 for Valsartan

SMEDDS. As from reports, it was found that at S/CoS (0.5/1) stable microemulsion

formation is not possible. Aliquots of each surfactant and co-surfactant mixture (Smix)

were then mixed with oil at ambient temperature. For each phase diagram, the ratio of oil

to the Smix was varied as 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9 (% v/v). Water was

added drop wise to each oil-Smix mixture under vigorous stirring. After equilibrium, the


Akshay R. Koli 153

samples were visually checked and determined as being clear microemulsion or emulsion

or gel. No heating is conducted during the preparation. These values of oil, surfactant and

co-surfactant were used to determine the boundaries of microemulsion region[17]

. After

the identification of microemulsion region in the phase diagrams, the microemulsion

formulations were selected at desired Surfactant : Co-surfactant (Smix) ratios. To

determine the effect of drug addition in SMEDDS, phase diagrams were constructed in

presence of drug. Black color shows self-microemulsion region and gray color indicates

microemulsion region. In order to prepare SMEDDS, selection of microemulsion region

from phase diagram was based on the fact that solution remains clear even on infinite

dilution[6, 15, 16]

. Phase diagrams were prepared using Pro-Sim ternary diagram software.

Results of phase diagram system are shown in Table 5.3.1.1 for Felodipine and Table

5.3.2.1 to 5.3.2.3 for Valsartan.

Results and Discussion

Pseudo-ternary phase diagrams were constructed to identify the Microemulsifying

regions. It has been observed that increasing concentration of the Surfactant within the

microemulsifying region caused increased spontaneity of self micro-emulsification

process. When a CoS was added to the system, it further lowered the interfacial tension

between the oil and water interface and also influenced the interfacial film curvature and

stability. On the other hand, safety should be considered with the increasing

concentration of S and CoS. All the combinations under test formed a microemulsion in

certain concentrations, but the combination with wider single phase region is considered

to be a better combination in terms of microemulsification efficiency.

5.3.1 Microemulsion System:

The system for Felodipine microemulsion is composed of oil (Capmul MCM),

surfactant:co-surfactant (Tween 20:PEG 400) and distilled water.


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Table 5.3.1.1: Water titration Reading for Phase diagram (Microemulsion System)

Oil (ml) Smix (ml) Dilution with water until system remained clear (ml)

4:1(S:CoS) 3:1(S:CoS) 2:1(S:CoS) 1:1(S:CoS)

0.3 2.7 infinite infinite Infinite Infinite

0.6 2.4 6.10 5.70 12.70 1.90

0.9 2.1 2.70 3.00 3.80 0.70

1.2 1.8 0.70 0.70 1.10 0.55

1.5 1.5 0.60 0.60 0.80 0.55

1.8 1.2 0.60 0.50 0.60 0.50

2.1 0.9 0.50 0.40 0.50 0.45

2.4 0.6 0.50 0.30 0.40 0.40

2.7 0.3 0.40 0.30 0.30 0.40

A B


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C D

Figure 5.3.1.1: Pseudo-ternary phase diagrams of Capmul MCM (oil), Tween20:

PEG 400 (S:CoS) and Water system

Microemulsion (Single phase region)

In microemulsion system, surfactant and co-surfactant get preferentially adsorbed at the

interface, reducing the interfacial energy as well as providing a mechanical barrier to

coalescence. The decrease in the free energy required for the emulsion formation

consequently improves the thermodynamic stability of the microemulsion formulation.

Therefore, the selection of oil and surfactant, and the mixing ratio of oil to S/CoS, play an

important role in the formation of the microemulsion. This can ascertain by pseudo-

ternary phase diagram as it differentiates the microemulsion region from that of

macroemulsion region. The water titration results for phase diagram are shown in Table

5.3.1.1 for Felodipine. One can select the microemulsion region from pseudo-ternary

phase diagram. As seen in figure 5.3.1.1, the microemulsion existence area increased as

the concentration of S:CoS ratio increased.

The grey region in the phase diagram is the one phase region which is the characteristic

of Microemulsion. As shown in Figure 5.3.1.1(A), for the 4:1 ratio of Tween 20:PEG 400

(S:CoS), more than 40% of S:Cos is required to stabilize 10% of the oil to make a single

phase system. The phase diagram shows that when S:CoS reduces less than 35%, coarse


Akshay R. Koli 156

emulsion forms having particle greater than 100 nm (Fig 5.3.1.1 A). Hence it can be

predicted that concentration of S:CoS should be more than 35% to form Microemulsion.

Higher concentration of oil leads to turbidity and coarse emulsion system. The decrease

in surfactant concentration in the system i.e. 3:1 ratio of S:CoS (Fig 5.3.1.1 B)didn’t

show any significant difference compared to the previous 4:1 ratio. In figure (Fig.

5.3.1.1(C)), 2:1 ratio of S/CoS covers maximum microemulsion region as compare to

other ratio of S/CoS. In this system, 40% of S/CoS can incorporate more than 12% of

the oil which is the highest incorporation of oil among all S:CoS ratio. Above these

concentrations coarse emulsion formed. When the ratio of S:CoS was 1:1 (Fig. 5.3.1.1

(D)), minimum microemulsion region was observed compared to other ratios and showed

fairly low incorporation of water to maintain visually clear microemulsion systems. It

involves formation of microemulsion which is unstable on dilution after 20% oil. Initially

it formed microemulsion but later on converted to emulsion as it moved towards higher

concentration of oil. Because of this, they were not selected for further investigation.

Hence putting into Nut Shell, 2:1 ratio of S/CoS forms better microemulsion region and

more water incorporation to form visually clear microemulsion compared to 1:1 ratio and

almost similar to 3:1 and 4:1 ratio and hence selected for further development and in all

the cases concentration of oil should be less than 20%v/v.

5.3.2 SMEDDS

Valsartan SMEDDS prepared using three different systems are summarized in Figure

5.3.2.1 considering the solubility study of the drug in various solvents. SMEDDS formed

oil in water microemulsion with gentle stirring, upon being introduced into aqueous

media. Since the free energy of the microemulsion is very low, the formation is

thermodynamically spontaneous. Surfactant and co-surfactant formed a layer around the

droplet of microemulsion, which not only reduced the interfacial energy but also

provided a mechanical barrier to coalescence. Generally, high proportion of oil in

microemulsion may result in high solubilization for poorly water-soluble drugs.

However, O/W microemulsions were not formed when SMEDDS with high proportions

of oil were diluted. Therefore, only SMEDDS with the law levels of oil were studied.


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(√: Ingredients used)

Figure 5.3.2.1: Excipients profiles for three different systems of SMEDDS

Table 5.3.2.1: Water titration Readings for Phase Diagram (V1)

V1: Oil (Capmul MCM), Surfactant : co-surfactant (Tween 80:PEG 400) and water.

Oil (ml) Smix (ml) Dilution with water until system remain clear (ml)

3:1(S:CoS) 2:1(S:CoS) 1:1(S:CoS)

0.1 0.9 Infinite Infinite Infinite


0.3 0.7 1.2 2.4 1.1

0.4 0.6 0.7 1.25 0.6

0.5 0.5 0.5 0.8 0.5

0.6 0.4 0.4 0.75 0.33

0.7 0.3 0.33 0.6 0.2

0.8 0.2 0.3 0.5 0.1

0.9 0.1 0.25 0.3 0.1

Ingredients V 1 V 2 V 3

Capmul MCM √ √ √

Tween 80 √ √

Labrasol √

PEG 400(CoS) √

Transcutol P (CoS) √ √

SMEDDS


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PEG 400 (S:CoS) and Water system

Self Microemulsion Microemulsion


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V2: Oil (Capmul MCM), Surfactant : co surfactant (Labrasol :Transcutol P) and

water.


3:1(S:CoS) 2:1(S:CoS) 1:1(S:CoS)

0.1 0.9 0.3 0.3 0.1

0.2 0.8 0.3 0.3 0.2

0.3 0.7 0.6 0.4 0.3

0.4 0.6 0.5 0.3 0.3

0.5 0.5 0.3 0.2 0.2

0.6 0.4 0.2 0.2 0.1

0.7 0.3 0.2 0.1 0.1

0.8 0.2 0 0 0

0.9 0.1 0 0 0


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Figure 5.3.2.3: Pseudo-ternary phase diagrams of Capmul MCM (oil), Labrasol:

Transcutol P (S:CoS) and Water system



V3: Oil (Capmul MCM), Surfactant:co surfactant (Tween 80:Transcutol P) and

water.


3:1(S:CoS) 2:1(S:CoS) 1:1(S:CoS)


0.2 0.8 Infinite Infinite 3.7

0.3 0.7 2.3 1.1 0.7

0.4 0.6 1.3 0.8 0.3

0.5 0.5 0.7 0.6 0.2

0.6 0.4 0.6 0.3 0.1

0.7 0.3 0.4 0.2 0.1

0.8 0.2 0.3 0.1 0.1

0.9 0.1 0 0 0


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Transcutol P (S:CoS) and Water system


Pseudo-ternary phase diagram for each formulation shown above represents presence of

microemulsion and emulsion regions. Black region represents self microemulsion domain

where as gray region indicates formation of microemulsion.


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SMEDDS forms microemulsion when titrated with water under agitation condition. The

particle size of microemulsion is less than 100 nm and as the energy required to form

microemulsion is very low, it is a thermodynamically spontaneous process[18]

. This

process is facilitated by presence of surfactant. The surfactant forms a layer around oil

globule in such a way that polar head lies towards aqueous and non polar tail pull out oil

and thereby reduces surface tension between oil phase and aqueous phase [20, 21]

. Another

factor affecting formation of microemulsion is the ratio of surfactant and co-surfactant.

The lipid mixtures with different surfactant, co-surfactant and oil ratios lead to the

formation of SMEDDS with different properties[22]

. Since surfactant and co-surfactant

adsorb at interface and providing mechanical barrier to coalescence, selection of oil,

surfactant, co-surfactant and mixing ratio to S/CoS, play important role in microemulsion

formation [23, 24]

. Nine different composition systems were prepared to study

pseudoternary phase diagram using surfactants and co-surfactants in varying ratio.

Generally, high proportion of oil in microemulsion may result in high solubilization for

poorly water-soluble drugs. However, no O/W microemulsion was formed when

SMEDDS with high proportion of oil were diluted.

System V1 was prepared using Capmul MCM as oil phase, Tween 80 as surfactant and

PEG 400 as co-surfactant. Formulation V1 A was prepared with surfactant : co-surfactant

(S:CoS) ratio of 3:1. As shown in Figure 5.3.2.2 (A), the point where amount of oil is less

than 10%, the water content is around 90%. At this point microemulsion can be diluted to

infinite which fulfills requirement of SMEDDS and also particle size of this

microemulsion is less than 100nm (described in characterization of SMEDDS). The

region where oil content is more than 20% and surfactant: co-surfactant is up to 60% also

forms the microemulsion but these were found to be unstable on dilution. The phase

diagram shows that when S:CoS reduces less than 40%, coarse emulsion forms having

particle greater than 100 nm (Fig 5.3.2.2 (A)). Hence it can be predicted that

concentration of Smix should be more than 40% to form self-microemulsion. Further,

more amount of oil also entrap less water content and thereby results in coarse emulsion.

As shown in Figure (Fig. 5.3.2.2 (B)), formulation V1 B covers maximum microemulsion

region as compare to all other formulations. Formulation V1B was prepared using similar


Akshay R. Koli 163

excipients but with S/CoS ratio of 2:1. In this system, after dilution amount of oil

contained was limited up to 20% and concentration of S/CoS was also 50%. At this point

and below, microemulsion can be diluted to infinite which fulfills requirement of

SMEDDS and also particle size of this microemulsion is less than 100nm (described in

characterization of SMEDDS). Above these concentrations coarse emulsion formed. The

third formulation V1C was prepared using S:CoS as 1:1. Formulation V1 C covers

minimum microemulsion region compared to V1 A and B. It involves formation of

microemulsion which is unstable on dilution after 20% oil (Fig. 5.3.2.2 (C)). Initially it

formed self microemulsion but later on converted to emulsion as it moved towards higher

concentration of oil. Hence putting into Nut Shell, in system V 1, composition B prepared

with 2:1 ratio of S/CoS forms better SMEDDS compared to other two formulations and

in all the cases oil concentration should be less than 20%.

The systems V2 were prepared using Capmul MCM as oil, Labrasol as a surfactant and

Transcutol P as a co-surfactant which produced three formulations A, B and C with

varying ratios of S:CoS to 3:1, 2:1 and 1:1 respectively. Formulation V2 A (Fig. 5.3.2.3

(V2A)) created microemulsion region with oil up to 10% and S/CoS 80% but at larger oil

concentrations it formed emulsion region having higher particle size which were not

stable for longer time. Also the requirement of surfactant volume for single phase region

in phase diagram was very high. Fig. 5.3.2.3 (V2B) and (V2C) showed comparatively

smaller microemulsion region. So it can be concluded that excipients used for V2 are

comparatively less suitable to form a SMEDDS then excipients of V1. It also suggests the

comparatively less effectivity of Labrasol as a surfactant than Tween 80. The possible

reason may the larger chain and greater solubilization capacity of Tween 80 than

Labrasol. Also the combination of Labrasol with Transcutol P may not be able to form

flexible, complex and easily reformable surface film. Thus it can be concluded that in

system V2, composition A prepared with 3:1 ratio of S/CoS forms better microemulsion

region compared to other two formulations and in all the cases oil concentration should

be less than 10%.

Next three compositions were prepared from third system V3 using Capmul MCM as oil,

Tween 80 as surfactant and Transcutol P as co-surfactant with S/CoS ratio of 3:1, 2:1 and


Akshay R. Koli 164

1:1 respectively. The V3 system has shown similar SMEDDS region as compared to

system V1. It may be due to the presence of Tween 80 in the formulations. The Figure

5.3.2.4 (V3 A, B and C) clarify that first two composition V3 A and composition V3 B

formed self microemulsion region with up to 20% oil concentration where as third

composition V3C did not show self-microemulsion region and stability of this

microemulsion was poor. Composition V3 A (Fig. 5.3.2.4 (V3A)) was prepared with

surfactant/co-surfactant (S/CoS) ratio of 3:1 which covers maximum microemulsion

region as compare to other V3 compositions. As shown in Figure 5.3.2.4 (V3A), the point

where amount of oil is less than 15%, the water content is more than 80%. At this point

microemulsion can be diluted to infinite which fulfills requirement of SMEDDS and also

particle size of this microemulsion is less than 100nm (described in characterization of

SMEDDS). The region where oil content is more than 15% and surfactant/cosurfactant is

up to 60% also forms the microemulsion but these were found to be unstable on dilution.

The phase diagram shows that when S/CoS reduces less than 40%, microemulsion region

decreases drastically and coarse emulsion forms having particle greater than 100 nm.

Hence it can be predicted that the concentration of S/CoS should be more than 40% to

form self-microemulsion. Further, more amount of oil also entrap less water content and

thereby results in coarse emulsion. Composition V1B was prepared using similar

excipients but with S/CoS ratio of 2:1. In this system, after dilution amount of oil

contained was limited up to 10%. At this point and below, microemulsion can be diluted

to infinite which fulfills requirement of SMEDDS and also particle size of this

microemulsion is less than 100nm (described in characterization of SMEDDS). Above

these concentrations coarse emulsion formed. The third composition V3C was prepared

using S/CoS as 1:1. Composition V3 C covers minimum microemulsion region compared

to V3 A and B. It involves formation of microemulsion which is unstable on dilution after

20% oil (Fig. 5.3.2.4 (V3C)). Initially it formed self microemulsion but later on converted

to emulsion as it moved towards higher concentration of oil. Hence putting into Nut

Shell, in V3, composition A prepared with 3:1 ratio of S/CoS forms better SMEDDS

compared to other two compositions and in all the cases oil concentration should be less

than 10%.


Akshay R. Koli 165

The Microemulsion region of V1 was higher than V3 in spite of having Tween 80 as

surfactant in both systems. The reason may be the different co-surfactants compositions

used in the compositions could have attributed to the difference in area of microemulsion

as in the case of V1 where PEG 400 was used while in V2 and V3 it was Transcutol P.

5.4 Effect of Drug loading on the phase diagrams of the

selected systems

The incorporation of drug has considerable influence on the phase behavior of the

spontaneously emulsifying systems. It has been reported that drug incorporation into

microemulsion can affect the microemulsion region in phase diagram[18]

. This can be due

to drug penetration into the surfactant monolayer producing perturbations at the interface

[18, 19].To verify this, the drugs were incorporated in to the selected oil:surfactant/Co-

surfactant system for Felodipine microemulsion and Valsartan SMEDDS and the area of

the one phase region was observed and compared with the area of one phase region

without drug.

5.4.1 Felodipine Microemulsion:

To verify the effect of drug loading on one phase region of the phase diagram, 20 mg/ml

(as per dose: 40mg/2ml) Felodipine was incorporated to Capmul MCM: Surfactant

mixture (Tween 20:PEG 400= 2:1) and studied for microemulsion region in phase

diagram by water titration.


Akshay R. Koli 166

Figure 5.4.1.1: Pseudoternary phase diagram of Capmul MCM, Tween 20 and PEG

400 (Placebo)

Figure 5.4.1.2: Pseudoternary phase diagram of Felodipine, Capmul MCM, Tween

20 and PEG 400

The phase diagrams indicating effect of Felodipine on phase behavior and area of

microemulsion existence are shown in figure 5.4.1.1 and 5.4.1.2. It was expected that

Felodipine would influence the phase behavior and the area of microemulsion formation


Akshay R. Koli 167

as in these formula, Felodipine was present in 20mg/ml. Phase diagrams studies indicated

that there was no difference observed in microemulsion region in the phase diagram

between the drug loaded and placebo composition. This suggests that the presence of

Felodipine does not affect the microemulsifying property of the composition.

5.4.2 Valsartan SMEDDS

Similar results were found when 40mg/ml (as per dose: 80mg/2ml) of Valsartan was

incorporated (10%w/w) to Capmul MCM: Surfactant mixture (Tween 80:PEG 400 = 3:1)

system and studied for microemulsion region in phase diagram by water titration. A slight

difference in microemulsion region in the phase diagram was observed between the drug

loaded and placebo SMEDDS mixtures. The results are shown in Figure 5.4.2.1 and

5.4.2.2 for placebo SMEDDS and Valsartan loaded SMEDDS.

It was expected that Valsartan would influence the phase behavior and the area of

microemulsion formation. Phase diagrams studies indicated that there was slight

influence of Valsartan on the area of microemulsion formation of the

Capmul:Tween80:PEG 400 based system. Incorporation of Valsartan in system led to a

slight reduction in the area of microemulsion formation of SMEDDS in Figure 5.4.2.1

when compared to the area in Fig. 5.4.2.2. Valsartan, due to its low aqueous solubility

and high surfactant mixture solubility, is likely to participate in the microemulsion by

orienting at the interface. The reduction in the area of microemulsion formation could be

due to Valsartan influenced interaction of surfactant and co-surfactant with oil.


Akshay R. Koli 168

Figure 5.4.2.1: Pseudoternary phase diagram of Capmul MCM, Tween 80 and PEG

400 (Placebo)

Figure 5.4.2.2: Pseudoternary phase diagram of Valsartan, Capmul MCM, Tween

80 and PEG 400


Akshay R. Koli 169

5.5 Preparation of Drug Loaded Microemulsions and

SMEDDS

Microemulsion and SMEDDS were prepared using the same method. However, the only

difference was that in preparation of SMEDDs, addition of water was not done as in

microemulsion. This SMEDDS is also known as microemulsion pre-concentrate because

when this SMEDDS come in contact with water it will convert into microemulsion

spontaneously. The flow chart for the preparation of drug loaded microemulsion is shown

below:

Fixed calculated quantity of oil, surfactant, co-surfactant & drug in completely dry

beaker was taken.

The drug was dissolved completely at room temperature under constant stirring on

the magnetic stirrer.

Figure 5.4.2.1: Flow Chart of preparation of SMEDDS and Microemulsion

SMEDDS

The required quantity of water was added drop wise with stirring.

Allowed to form a clear and transparent liquid.

Microemulsion


Akshay R. Koli 170

5.5.1 Felodipine Microemulsion:

A series of formulations were prepared with varying ratios of oil, surfactant and co-

surfactant. Formulations F1 – F9 were prepared using Capmul MCM as oil, Tween 20 as

surfactant and PEG 400 as co-surfactant to optimize the concentration of oil and Smix, For

microemulsion system, three different oil concentrations i.e 5%, 10% and 15% and three

different concentrations of Smix i.e 40%, 45% and 50% were used. These concentrations

were selected based on preliminary studies and pseudoternary phase diagram i.e. above

15% oil concentration, turbidity occurred and upto 50% Smix was sufficient to make clear

microemulsion. The compositions are shown in Table 5.5.1.1.

Table 5.5.1.1: Compositions of Felodipine Microemulsion Systems (Batch F1 – F9)

In all the formulations, the level of Felodipine was kept constant (i.e. 20 mg/ml of

Felodipine). Briefly, oil, surfactant and co-surfactant were accurately weighed into glass

vials according to their ratios. The Felodipine (20 mg/ml) was added in the mixture.

Batch no. Felodipine

(mg/ml)

Oil

%v/v

Smix (2:1)

% v/v

F1 20 5 40

F2 20 5 45

F3 20 5 50

F4 20 10 40

F5 20 10 45

F6 20 10 50

F7 20 15 40

F8 20 15 45

F9 20 15 50


Akshay R. Koli 171

Then, the components were mixed by gentle stirring and vortex mixing until Felodipine

was completely dissolved. The mixture was stored at room temperature until used. So,

prepared concentrate of microemulsion was composed of oil, surfactant, co-surfactant

and drug. Water was added to microemulsion concentrate to make up the volume up to

100. The compositions which were optically clear have been evaluated further by

constructing phase diagrams.

5.5.2 Valsartan SMEDDS:

A series of formulations were prepared with varying ratios of oil, surfactant and co-

surfactant. Formulations V1 (Table 5.5.2.1) were prepared using Capmul MCM as oil,

Tween 80 as surfactant and PEG 400 as cosurfactant. Similarly formulations V2 (Table

5.5.2.2) were prepared with Capmul MCM as oil, Labrasol as surfactant and Transcutol P

as cosurfactant. Third system containing formulations V3 (Table 5.5.2.3) were prepared

using combination of Capmul MCM, Tween 80 and Transcutol P as an oil, surfactant and

co-surfactant respectively. In each system three formulations were prepared by varying

ratio of Oil in three levels i.e 5%, 7.5% and 10% v/v with the optimized ratio of

Surfactant mixture (S:CoS) as per the pseudo ternary phase diagram study (Section 5.3).

For Tween 80: PEG 400 system (V1), highest one phase region was found in 2:1 ratio by

pseudoternary phase diagram and hence selected as further preparation. For Labrasol:

Transcutol P system (V2), highest one phase region was found in 3:1 ratio and hence

selected for further preparation. For Tween 80: Transcutol P (V3) system, highest one

phase region was found in 3:1 ratio and hence selected for further preparation.

Formulations A, B and C were prepared by taking the concentration of oil as 5%, 7.5%

and 10%. In each formulation concentration of valsartan was kept constant to 40 mg/ml.

The volume of Valsartan SMEDDS was kept 2ml. The concentrations of oil, surfactant,

and cosurfactant for Valsartan SMEDDS are recorded in Table 5.5.2.1 (V1), Table

5.5.2.2 (V2) and Table 5.5.2.3 (V3).


Akshay R. Koli 172

Table 5.5.2.1: Compositions of Valsartan SMEDDS 1 (V1)

Ingredients (% v/v) A B C

Valsartan (mg/ml) 40 40 40

Capmul MCM 5 7.5 10

Tween 80 63.3 61.7 60

PEG 400 31.7 30.8 30

Oil- Capmul MCM, Surfactant- Tween 80, Co-surfactant- PEG 400 (S:CoS=2:1)


Vehicle (% v/v) A B C


Capmul MCM 5 7.5 10

Labrasol 71.2 69.4 67.5

Transcutol P 23.8 23.1 22.5

Oil- Capmul MCM , Surfactant- Labrasol, Co-surfactant- Transcutol P (S:CoS=3:1)


Vehicle (% v/v) A B C


Capmul MCM 5 7.5 10

Tween 80 71.2 69.4 67.5

Transcutol P 23.8 23.1 22.5

Oil- Capmul MCM, Surfactant- Tween 80, Co-surfactant- Transcutol P (S:CoS=3:1)


Akshay R. Koli 173

All the prepared compositions of Felodipine Microemulsion (Batches F1 – F9) and

Valsartan SMEDDS (Batches V1 A,B,C / V2 A,B,C / V3 A,B,C) were further carried

forward for characterization and optimization in chapter 6.


Akshay R. Koli 174

5.6 References

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