ENCAPSULATION OF VENLAFAXINE HCL IN TO POLY-E-CAPROLACTONE MICROSPHERES BY W/O/W AMD W/O/O EMULSION SOLVENT EVAPORATION TECHNIQUE AND COMPARISON FOR ITS CONTROLLED RELEASE PROPERTIES

* Manabendra Rabha 1 and Dr. Bipul Nath 2 . 1. M. Pharm., Department of Pharmaceutics, Girijananda Institute of Pharmaceutical Sciences, Azara, Guwahati, Assam-781017, India. 2. Girijananda Chowdhury Institute of Pharmaceutical Science, Azara, Guwahati-781017, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


ISSN: 2320-5407
Int. J. Adv. Res. 5 (7), 836-842 837 combined enclosed with a drug in such a way that the active agent is released from the material in a pre-designed manner. These particulate based systems for the delivery of drugs are believed to enhance bioavailability, predictable therapeutic response, greater efficacy and safety and controlled and prolonged drug release profile. It provides effective treatment at the site of action at much lower doses. They are especially important in the case of poor drug distribution at the site of infection due to limited blood circulation to the surrounding skeletal tissue(Di Silvio and Bonfield, 1999;Paul and Sharma, 2003). The theory that polymers could be used as drug carriers to provide the controlled release of drug(s) is now well established. Biodegradable polymers are extensively employed in controlled-release drug delivery devices because of their abundant source, lack of toxicity, high tissue compatibility and they are the possible means of delivering drugs by several routes of administration. Among synthetic materials, biodegradable polyesters, approved by the Food and Drug Administration (FDA) for human use, are rapidly gaining recognition. Poly(e-caprolactone) (PCL) is a well-known hydrophobic, synthetic polyester with excellent tissue compatibility, biodegradability and existing regulatory approval (Hombreiro Pérez et al., 2000;Lionzo et al., 2007). Degradation of PCL in comparison to poly (lactide-co-glycolide) (PLGA) and other polymers is slow, making it suitable for long-term delivery extending over a period of more than 1 year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanoparticles and implants.
Venlafaxine HCl is a new generation antidepressant serotonin / noradrenalin reuptake inhibitor drug showing effective anti-depressant properties. It has a short oral bioavailability of 45% and biological half-life of 4-5 hours. The total daily dose of Venlafaxine is 225-375 mg/day in moderate and severe depressive disorder. So, frequent administration is necessary to maintain its therapeutic concentration. This necessitates of frequent administration of large doses (75 mg every 4 to 5 h three times daily or four times daily) to maintain therapeutic drug level (https://dailymed.nlm.nih.gov/dailymed/archives/fdaDrugInfo.cfm?archiveid=9595, 12/2008).
The side effects of Venlafaxine are dose dependent and a reduction of the total administered dose reduces the severity of the toxicity. Thus the short half-life of 4 h and frequent dosing of large doses due to low oral bioavailability makes Venlafaxine a good candidate for microencapsulation. Hence, there is a need for developing sustained release dosage form of Venlafaxine that maintains improved bioavailability and therapeutic plasma drug concentration for long period compared to conventional dosage forms.
Microencapsulation may improve the absorption of a drug and maintain its plasma concentration within the therapeutic index. Ibrahim et al, 2016 reported about formulation of Venlafaxine for once daily administration using polymeric material hybrids. The developed formulation of PLA/ Eudragit at 1:1 ratio sustained the drug release up to 24 h with low burst release. This formula had higher Venlafaxine absorption in rabbits compared to the commercial capsules(Ibrahim and Salah, 2016).

Materials and Methods:-
Materials:-Venlafaxine hydrochloride was purchased from Merck pvt ltd and poly-e-caprolactone was purchased from Sigma Aldrich (Bangalore).

Preparation of microspheres:-Preparation of poly-e-caprolactone microspheres by two different emulsion solvent evaporation techniques: W/O/W Method:-
Double emulsion method of microspheres preparation involves the formation of the multiple emulsions or the double emulsion of type w/o/w. The Venlafaxine hydrochloride is mixed in 2 ml of distilled water. Simultaneously polymer poly-e-caprolactone is dispersed in Dichloromethane. Now the drug solution is mixed in the polymer solution and emulsified. The continuous phase is consisted of the polymer solution that will encapsulate the drug contained in dispersed aqueous phase. The primary emulsion will then be subjected to the homogenization or the sonication before addition to the aqueous solution of the poly vinyl alcohol (PVA) and water. This will results in the formation of a double emulsion. The emulsion will be then subjected to solvent removal by solvent evaporation (Naik et al., 2012).

W/O/O Method:-
The Venlafaxine hydrochloride is mixed in 2 ml of distilled water. Simultaneously polymer poly-e-caprolactone is dispersed in Dichloromethane. Now the drug solution is mixed in the polymer solution and emulsified. The continuous phase is consisted of the polymer solution that will encapsulate the drug contained in dispersed aqueous phase. The primary emulsion will then be subjected sto the homogenization or the sonication before addition to the 838 solution of span 80 and 0.5% w/v liquid parrafin. This will results in the formation of a double emulsion. The emulsion will be then subjected to solvent removal by solvent evaporation (Naik et al., 2012).

Compatibility study of Drug:-DSC & FT-IR study of formulations:-
The DSC was done to analyse physical state of drug in the microspheres. The thermograms of the microspheres with polymer were obtained at a scanning rate of 10°C/min conducted over a temperature range of 40-350ºC. The FTIR analysis will carried out of the prepared microsphere with FT-IR instrument (Bruker 100597, Model: Alpha, Germany). A small amount of pure drug and crushed formulation was kept on the sample holder and scanned from 4000 cm -1 to 400cm -1 to evaluate the physical state of the drug.
Evaluations of microspheres:-Particle size Analysis:-Microsphere size was determined using an optical microscope under regular polarised light. The mean microsphere size was calculated by measuring 100 particles.

Percentage Yield:-
The percentage yield of different formulations was determined by weighing the microspheres after drying and comparing with the total amount of drug and polymer required formulating these formulations. Percentage yield was calculated as follows, % yield = × 100

Drug entrapment Efficiency:-
The Venlafaxine content of biodegradable microspheres will be determined for all the formulations by dissolving 10mg of microspheres in 200mL of DCM taken in 2mL tubes and vortexed for 10 min. The ethanol (1800mL) will be added and vortexed for another 5 min followed centrifugation at 3000 rpm for 10 min to settle down the PCL precipitated. The supernatant containing Venlafaxine is suitably diluted using ethanol and the absorbance will be measured at 370nm by UV-Vis spectrophotometry and equivalent concentration was determined using the calibration curve prepared using the same proportion of solvents. The percentage (%) drug loading (DL) and percentage (%) entrapment efficiency (EE) of the blend microspheres will be calculated using the following formula.

Scanning electron microscopy (SEM):-
The shape and surface characteristics of the microspheres were observed by scanning electron microscope (SEM). The microsphere sample was thinly sprinkled onto a metal stub and vacuum coated with thin layer of gold in argon atmosphere. The SEM photomicrographs of the coated particles were obtained at 15kv using a ZEISS,Germany scnning electron microscope.

In -vitro release studies:-
The in vitro dissolution of the formulations were determined by employing USP type 1 rotating basket method (900 ml phosphate buffer of pH 1.2 ,100 rpm, 37±0.5°C).Microspheres equivalent to 100mg of drug will be loaded in the basket of the dissolution apparatus. 5ml of sample were withdrawn from the dissolution medium at suitable time intervals and the same was replaced with same phosphate buffer of pH 1.2 to maintain sink condition. The absorbance of the filtrate was determined at wavelength 274nm by using UV visible spectrophotometer against phosphate buffer of pH 1.2 as blank and amount of drug in the filtrate will be determined from the calibration curve and cumulative percent of drug release was calculated.

Kinetic evaluation of in-vitro release Data:-
In order to study the exact mechanism of drug release from the microspheres, drug release data were analysed according to zero order, 1st order, Higuchi square root and Korsemeyer-Peppas equations. The in-vitro release data which were obtained from optimised formulation in the dissolution medium were fitted to different kinetic models.

% yield study:-
The yield of the microspheres prepared by both the techniques was between 75 to 85%. It showes that the utilised methods provide good yield of microspheres, where the w/o/w method provides marginally better yield than w/o/o method (Table 1).

Particle size Determination:-
Venlafaxine HCl was successfully encapsulated and the microspheres were predominantly round and smooth with a mean particle size ranging from130-135 μm in w/o/w method, while the particles are round with a mean size ranging from 120 to 124 μm in the case of w/o/o method (Table 1).  (Table 1).   (Figure 3) revealed that microspheres possess almost smooth surface and spherical shape while cracks were also present on the surface of microspheres and clumps were also present .SEM photographs revealed the absence of crystals of drug on the surface of the microspheres, indicating uniform distribution of drug within these microspheres.

In-vitro Release Study:-
Release studies reveals that the release behavior of drug was governed by the microstructure of PCL microparticles, suggesting that the environment for diffusion changes according to processing conditions such as polymer solution concentration, thermal history, and polymer molecular weight. The release profiles of VLF from the microspheres prepared using o/o/o method, with organic solvent blend (dichloromethane: ethanol), showed a burst release of about 60 to 90% after first one hour. W/O/W method showed a burst release of about 35 to 40% after first one hour. The burst release is directly proportional to their total entrapment values. There was a gradual increase in the drug release till the 6 hr in all the batches and after wards the release was very slow. About 60% of the VLF was released in 12 hours. The % cumulative drug release from all formulations is represented in Figure 4.

Kinetic evaluation of in vitro release Data:-
The in vitro release kinetics of the Venlafaxine loaded microspheres was poltted in various kinetic models and represented in Table 2. The release constants for formulations F1-F6 were calculated from the slope of the appropriate plots, and regression coefficient (r 2 ) by linear regression analysis. The zero-order release values for formulations were 0.294-0.535 and 0.598-0.724 for first order ( Table 3). The F1-F6 formulations release regression values (r 2 ) were best fitted with the Higuchi plot with a regression range of 0.881-0.938 rather than first and zero orders (Table 3). But the F4, F5 and F6 showed a similar type of regression range. Thus the drug release of Venlafaxine was proportional to the square root of time, indicating diffusion controlled-release mechanism for all the formulations. While the marketted formulation (F7) showed first order release pattern for Venlafaxine. Further study on Korsmeyer-Peppas model revealed that the exponent values were found to lie within a range of 0.948 and 0.955 and the release exponent (n) values were found in between 0.31-0.39 (n<0.5) indicating a Fickian type of release mechansim.

Conclusion:-
On account of the present study, it can be concluded that Venlafaxine was successfully microencapsulated into polyε-caprolactone micropsheres by both the double emulsification methods. Out of these two different emulsion methods w/o/o gives better entrapment efficiency and controlled release characteristics as compared to w/o/w method. PCL appeared to be promising carrier for Venlafaxine HCl controlled release formulations, because of its biodegradability and biocompatibility. Also the prepared Venlafaxine HCl loaded poly-ε-caprolactone microspheres released the drug over extended period of time which strengthen its approach as a possible candidate for controlled drug delivery.