International Journal of Drug Development and Research

Keywords

Telmisartan, S-SMEDDS, Neusilin US2, Pseudo ternary phase diagram

INTRODUCTION

The poor solubility and low dissolution rate of poorly water soluble drugs in the aqueous gastro-intestinal fluids frequently cause deficient bioavailability. Particularly for BCS class II substances, the bioavailability may be enhanced by increasing the solubility and dissolution rate of the drug in the gastro-intestinal fluids.[1] Self micro emulsifying drug delivery systems (SMEDDS) are isotropic mixtures of drug, lipids and surfactants, usually with one or more hydrophilic cosolvents or coemulsifiers. Upon mild agitation followed by dilution with aqueous media, these systems can form fine (oil in water) emulsion instantaneously.[2] SMEDDS are generally encapsulated either in hard or soft gelatin capsules. Lipid formulations however may interact with the capsule resulting in either brittleness or softness of the shell.[3] To overcome this problem SMEDDS need to convert into Solid SMEDDS. The major techniques for converting SMEDDS to S-SMEDDS are spraycooling, spray drying, adsorption onto solid carriers, melt granulation, melt extrusion, super-critical fluid based methods and high pressure homogenization. But adsorption process is simple and involves simply addition of the liquid formulation to solid carriers by mixing in a blender.[4]

TEL is 2-(4-{[4-methyl-6-(1-methyl-1H-1,3- benzodiazol-2-yl)-2-propyl-1H-1,3-benzodiazol-1-yl] methyl} phenyl) benzoic acid with log P value 3.2. It belongs to class II drug in BCS classification. TEL is Angiotensin II receptor antagonist, which is used in the prevention and treatment of hypertension. The solubility of TEL in aqueous medium is very low. Absolute bioavailability of the TEL is 42-58% and biological half-life is 24 hours that results into poor bioavailability after oral administration. Hence it is necessary to increasing aqueous solubility and dissolution of TEL.[5,6,7] Neusilin US2 is a fine ultra light granule of magnesium aluminometasilicate and is widely accepted as a multifuntional excipient that improves the quality of pharmaceuticals. Due to its large surface area and porous nature, Neusilin US2 adsorbs high loads of oils or water and can be mechanically compacted into high quality tablets.[8] It exhibit high adsorbing capacity and can be used to convert SMEDDS to S-SMEDDS.[9, 10] Hence in this study S-SMEDDS of TEL was prepared using Neusilin US2 by adsorption technique for enhancement of dissolution rate.

MATERIALS AND METHODS

MATERIALS:

TEL was obtained as a gift sample from Glochem Industries Ltd. Vishakhapatnam, AP, India. Neusilin US2 was gifted by Fuji chemicals Japan. Oleic acid was obtained from Loba Chemie Pvt. Ltd., Mumbai. PEG 400, Tween 80 were obtained from S. D. Fine Chem., Mumbai. All other chemicals were of reagent grade.

METHODS:

Identification of micro emulsion region by constructing pseudo ternary phase diagram:

From solubility study Oleic acid, Tween 80 and PEG 400 were selected as oil, surfactant and co-surfactant respectively and for preparation of stable SMEDDS, micro emulsion region was identified by constructing pseudo ternary phase diagram containing different proportion of surfactant: co-surfactant (Km value 1:1, 2:1 and 3:1), oil and water. In brief Smix and oil were mixed at ratio of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 and 9:1 in pre-weighed test tube. To the resultant mixtures, double distilled water was added drop wise till the first sign of turbidity in order to identify the end point and after equilibrium; if the system became clear then the water addition was continued.[11, 12, 13]

Preparation of Liquid SMEDDS

The phase diagrams were constructed at different Km values and the Km value at which high micro emulsion region obtained was selected for formulation of Liquid SMEDDS. In brief TEL (20 mg/10gm) was placed in glass vial. To this Oleic acid (10 % w/w) added and warmed on water bath. To this oily mixture Tween 80 and PEG 400 in the proportion of 3:1 (40 % w/w) was added. Then the components were mixed by gentle stirring and vortex mixing at 37 ºC until TEL was completely dissolved. Then the mixture was sealed in glass vial and stored at room temperature until used.[14]

Evaluation of Liquid SMEDDS [15, 16, 17, 18]

Thermodynamic Stability Studies

Thermodynamic stability study of prepared SMEDDS was determined by carrying heating cooling cycle, centrifugation test and freeze thaw cycle.

Heating cooling cycle

Six cycles between refrigerator temperatures 4ºC and 45ºC with storage at each temperature for not less than 48 hours was studied. If SMEDDS stable at these temperatures was subjected to centrifugation test.

Centrifugation test

Passed SMEDDS was centrifuged at 3500 rpm for 30 min using digital centrifuge (Remi motors Ltd.). If SMEDDS did not show any phase separation was taken for freeze thaw stress test.

Freeze thaw cycle

Three freeze thaw cycles between -21ºC and +25ºC with storage at each temperature for not less than 48 hours was done for SMEDDS.

Robustness to dilution

Robustness to dilution was studied by diluting Liquid SMEDDS to 50, 100 and 1000 times with water, buffer pH 1.2 and buffer pH 7.5. The diluted SMEDDS were stored for 12 h and observed for any signs of phase separation or drug precipitation.

Assessment of Efficiency of selfemulsification

Efficiency of self-emulsification was assessed by procedure used by Khoo Shui-Mei et.al. (1998) using USP- type-II dissolution test apparatus (Veego VDA- 8DR). 1 mL of Liquid SMEDDS was added drop wise to 200 ml of 0.1 N HCl at 37°C. Gentle agitation was provided by a standard stainless steel dissolution paddle rotating at 60 rpm. SMEDDS assessed visually according to the rate of emulsification and final appearance of the emulsion.

% Transmittance

1 mL of Liquid SMEDDS was diluted to 100 mL distilled water and observed for any turbidity and % transmittance was measured at 650 nm using UV–vis spectrophotometer (Shimadzu-1800, Japan) against distilled water as a blank.

Globule size, PDI and Zeta potential

Liquid SMEDDS was diluted to 10 times with distilled water and globule size, PDI and zeta potential were determined using Malvern Zetasizer (Nano ZS90).

Dye solubilization test

So as to confirm the oil in water nature of SMEDDS a water soluble dye Eosin was sprinkled onto the surface of prepared microemulsion and observed for spontaneous dispersion

Cloud point measurement

Liquid SMEDDS was diluted with distilled water in the ratio of 1:250, placed in a water bath and its temperature was increased gradually. Cloud point was measured as the temperature at which there was a sudden appearance of cloudiness visually.

Formulation of S-SMEDDS

S-SMEDDS was prepared by mixing liquid SMEDDS containing TEL with Neusilin US2 in 1:1 proportion. In brief liquid SMEDDS was added drop wise over Neusilin US2 contained in broad porcelain dish. After each addition, mixture was homogenized using glass rod to ensure uniform distribution of formulation.[20]

Evaluation of S-SMEDDS

Micromeritic properties of S-SMEDDS[21, 22]

Prepared S-SMEDDS was evaluated for micromeritic properties such as angle of repose, bulk and tapped density, compressibility index and Hausner ratio.

Determination of drug content

Drug content was estimated by extracting TEL from S-SMEDDS. In brief S-SMEDDS was dissolved in sufficient quantity of methanol. Solution was sonicated for 10-15 min for extraction of the TEL in methanol and filtered. The absorbance of filtrate was read at 296 nm on UV- Visible Spectrophotometer (Shimadzu-1800, Japan).[23]

Reconstitution properties of S-SMEDDS

Dilution study by visual observation

Dilution may better mimic the condition of stomach after oral administration. Hence effect of dilution on S-SMEDDS was studied. S-SMEDDS (100 mg) was introduced into 100 mL of double distilled water in a glass beaker that was maintained at 37ºC and the contents mixed gently using a magnetic stirrer. The tendency to emulsify spontaneously and progress of emulsion droplets were observed with respect to time. The emulsification ability of S-SMEDDS was judged qualitatively “good” when clear microemulsion formed and “bad” when there was turbid or milky white emulsion formed after stopping of stirring.[24]

% Transmittance, Globule size, PDI, Zeta potential

Reconstituted S-SMEDDS were also characterized for % Transmittance, Globule size, PDI, Zeta potential as described for liquid SMEDDS.

FTIR study of S-SMEDDS

FTIR spectrum was recorded for TEL, TEL: Neusilin US2 physical mixture and prepared S-SMEDDS using Agilent Cary 630 FTIR spectrometer.

Scanning electron microscopy

Scanning electron micrographs for TEL, Neusilin US2 and prepared S-SMEDDS was taken using Scanning electron microscope (JEOL, Japan) at accelerating voltage at 3-5 kV to study surface topography.

Differential scanning calorimetry

Physical state of TEL in S-SMEDDS was characterized using differential scanning calorimeter. Thermograms of TEL, Neusilin US2 and S-SMEDDS were obtained using differential scanning calorimeter. (TA Instruments SDT-2960, USA)

In-vitro dissolution study

The in-vitro dissolution study of S-SMEDDS and plain TEL were carried out using USP- type-II dissolution test apparatus in pH 1.2 and pH 7.5 buffer solutions at 37±0.50C with 50 rpm rotating speed. Samples of 5 mL were withdrawn at regular time interval of 5, 10, 15, 30, 60 and 120 min and filtered using 0.45 μm filter. An equal volume of respective dissolution medium was added to maintain the volume constant. Drug content from sample was analyzed using UV-spectrophotometer at 296 nm. All measurements were done in triplicate from three independent samples.[23]

RESULTS AND DISCUSSION

Identification of micro emulsion region by constructing pseudo ternary phase diagram

Nine different potential combination of surfactant mixture to oil at different Km values (1:1, 2:1 and 3:1) were used for construction of pseudo ternary phase diagram which is presented in Figure 2. Shaded area in phase diagram shows micro emulsion region. Phase behavior examination of this system established an appropriate approach to determine concentration of oil, surfactant: co-surfactant and water so that transparent, monophasic low viscous micro emulsion can be formed. Phase diagram at Km value 3:1 showed maximum micro emulsion region.[12] So that maxium proportion of oil can be incorporate in the system which will helpful for solubalization of TEL, hence selected for further study. Hence optimum formulation of micro emulsion contained Oleic acid (10 %), Tween 80:PEG 400 (40%) and Water 50 %

Evaluation of Liquid SMEDDS

Thermodynamic Stability Studies

Physical stability of SMEDDS was essential to its performance, which can be ominously affected by precipitation of the drug. In addition, the formulation having poor physical stability can affects the formulation performance and it also leads to phase separation. Hence thermodynamic stability studies were performed by performing heating cooling cycle, centrifugation test and freeze thaw cycle. It was observed that, formulation was passed the heating cooling cycle test hence, further exposed to centrifugation test. SMEDDS did not show any phase separation after centrifugation test hence; was taken for freeze thaw stress test. After freeze thaw stress test, it was found that SMEDDS showed good stability with no phase separation, creaming or cracking.

Robustness to dilution

After diluting Liquid SMEDDS to 50, 100 and 1000 times with water, buffer pH 1.2 and buffer pH 7.5 and storing for 12 h it was observed that there was no any signs of phase separation or drug precipitation.

Assessment of Efficiency of selfemulsification

The in-vitro performance of SMEDDS was visually assessed using the grading system used by Khoo Shui-Mei et.al. (1998) and it was found that, SMEDDS rapidly formed micro emulsion within 1 min which was clear and slightly bluish in appearance as per grade A.

% Transmittance, Globule size, PDI and Zeta potential:

Percent transmittance of reconstituted liquid SMEDDS was found to be 88.7 ±0.67. Globule size was found to be 30.2 nm with polydispersity index 0.116. Zeta potential of liquid SMEDDS was found to be -5.80 mV.

Dye solubilization test and Cloud point measurement

The type of emulsion was confirmed by using dye solubilization test. Rapid incorporation of the watersoluble dye (eosin) into the system was observed which indicate that the continuous phase was water, which signified the formation of o/w micro emulsion. Cloud point of prepared liquid SMEDDS was found to be higher than 85oC, which indicate that micro emulsion will be stable at physiological temperature without risk of phase separation.

Micromeritic properties and drug content of S-SMEDDS

Micromeritic properties such as angle of repose, bulk and tapped density, compressibility index, Hausner ratio, etc and drug content of S-SMEDDS are shown in Table:1. Results showed that prepared S-SMEDDS shows good flow properties and drug content.

Reconstitution properties of S-SMEDDS Dilution study by visual observation

S-SMEDDS showed spontaneous micro emulsification and there was no sign of phase separation or phase inversion of micro emulsion after storage of 2 h.

% Transmittance, Globule size, PDI, Zeta potential

Percent transmittance of reconstituted S-SMEDDS was found to be 92.8 ±0.32. It indicates that reconstituted S-SMEDDS was found to be clear. Results Globule size with PDI and Zeta potential are shown on Figure 3 and 4 respectively. Globule size was found to be 32.4 nm with polydispersity index 0.219 and zeta potential was found to be -6.32 mV.

FTIR study of S-SMEDDS

Figure 5 shows FTIR spectrum of TEL, TEL:Neusilin US2 physical mixer and S-SMEDDS. Results showed that deformation of characteristic peaks of TEL in SSMEDDS which may be due to formation of amorphous state of TEL.

Scanning electron microscopy

Scanning electron micrograph of plain TEL, Neusilin US2 and S-SMEDDS are shown in Figure 6. This indicate that S-SMEDDS appeared as smooth surfaced particles, indicating that liquid SMEDDS is adsorbed or coated inside the pores of Neusilin US2 without agglomeration.

Differential scanning calorimetry

DSC curves of TEL, Neusilin US2 and S-SMEDDS is shown in Figure 7. TEL shows sharp endothermic peak at near about 267.1-269.6oC. Neusilin US2 shows peak at 201.2-231.8oC The S-SMEDDS exhibit retained small endothermic peak for TEL at 268.4oC and it may be due to solubilization of TEL in SMEDDS.

In-vitro dissolution study

Figure 8 shows cumulative percent drug release of SSMEDDS and Plain TEL in pH 1.2 and 7.5. Cumulative % drug release of TEL in pH 1.2 and 7.5 was found to be 95.35± 2.25 and 99.78± 2.34 respectively and that of plain TEL was found to be 29.35± 1.36 and 31.47± 2.06 respectively. This showed that drug releases from S- SMEDDS was found to be significantly higher as compared to plain TEL and it was also found that, dissolution of TEL is pH independent.

CONCLUSION

From study it was concluded that, prepared liquid SMEDDS was thermodynamically stable with good self emulsification efficiency and having globule size in nanometric range which may be physiologically stable. Study also concluded that, S-SMEDDS of TEL prepared with Neusilin US2 by adsorption technique have good flow property and drug content. After reconstitution S-SMEDDS formed clear micro emulsion with nanometric size. Results of SEM demonstrate that spherical S-SMEDDS can be obtained without agglomeration. In-vitro drug release of S-SMEDDS was much higher than that of plain TEL. Hence it was concluded that S-SMEDDS can be efficiently formulated by adsorption technique using Neusilin US2 as solid carrier to enhance dissolution rate of poorly soluble drug such as TEL.

ACKNOWLEDGEMENT

Authors would like to thank Hon. Shri. G. D. Patil, Secretary, Shree Warana Vibhag Shikshan Mandal, Warananagar, Kolhapur, MS India, for constant inspiration and making available the necessary facilities and Fuji Chemicals, Japan for providing gift sample of Neusilin US2.

Tables at a glance

Table 1

Figures at a glance

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

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