Formulation , and Evaluation of Pentoxifylline-Loaded Poly ( ε-caprolactone ) Microspheres

Indian Journal of Pharmaceutical Sciences 333 May June 2008 The main objective of any drug therapy is to achieve a desire concentration of the drug in blood or tissue which is therapeutically effective and nontoxic for extended period of time, and this goal can be achieved by proper design of sustain release dosage regimen1,2. Microspheres have been widely accepted as a mean to achieve oral and parenteral controlled release3,4. The microspheres require a polymeric substance as a coating material or carrier5. A number of different substances biodegradable as well as non-biodegradable have been investigated6 for the preparation of microspheres. Of the various biodegradable polymers used for the development of sustained release formulations, poly(є-caprolactone) has been reported to be advantageous since they are biocompatible7,8. Poly(є-caprolactone) is aliphatic polyester polymer, suitable for controlled drug delivery due to a high permeability to many drugs and at the same time being free from toxicity9,10.

The main objective of any drug therapy is to achieve a desire concentration of the drug in blood or tissue which is therapeutically effective and nontoxic for extended period of time, and this goal can be achieved by proper design of sustain release dosage regimen 1,2 .Microspheres have been widely accepted as a mean to achieve oral and parenteral controlled release 3,4 .The microspheres require a polymeric substance as a coating material or carrier 5 .A number of different substances biodegradable as well as non-biodegradable have been investigated 6 for the preparation of microspheres.Of the various biodegradable polymers used for the development of sustained release formulations, poly(є-caprolactone) has been reported to be advantageous since they are biocompatible 7,8 .Poly(є-caprolactone) is aliphatic polyester polymer, suitable for controlled drug delivery due to a high permeability to many drugs and at the same time being free from toxicity 9,10 .
Pentoxifylline, a xanthine derivative, is an analogue of theophylline and inhibits phosphodiesterase.Pentoxifylline and its metabolites improve the ß ow properties of blood by decreasing its viscosity.In patient with chronic peripheral arterial disease, this increase blood ß ow to the affected microcirculation and enhance tissue oxygenation.Pentoxifylline has short half-life of 1.6 h and low oral availability (19±13%) 11 .The aim of this study was to prepare poly(є-caprolactone) microspheres containing pentoxifylline to achieve a controlled drug release proÞ le suitable for peroral administration.

MATERIALS AND METHODS
Pentoxifylline was obtained as a gift sample from Shreya Health Care, Aurangabad.Poly(є-caprolactone) was obtained from Fulka Cemika, Sigma-Aldrich Chemie, Switzerland.Dichloromethane was procured from Loba Chem.Pvt. Ltd., Mumbai.All other reagents used were of analytical grade.

Kinetics of drug release:
In order to understand the mechanism and kinetics of drug release, the result of the in vitro dissolution study of microspheres were Þ tted with various kinetic equations, like zero order 20 (percentage release vs. time), Þ rst order 21 (log percentage of drug remaining to be released vs. time) and Higuchi's model 22 (Percentage drug release vs. square root of time).Correlation coefÞ cient (r 2 ) values were calculated for the linear curves obtained by regression analysis of the above plots.dissolved in this polymer phase.This solution was poured in 100 ml of liquid parafÞ n containing 1.3% Tween 80 and continuous stirred for 5 h at 1100 rpm.The microspheres were filtered and washed three times with 50 ml of n-hexane and dried at room temperature for 12 h.Microspheres dried at room temperature were then weighed and the yield of microspheres preparation was calculated using the formula 14 , Percent yield = (Amount of microspheres obtained/The theoretical amount)"100

Evaluation of the microspheres:
Pentoxifylline was extracted from the microspheres after crushing with phosphate buffer pH 7.4 and absorbance was measured using UV/Vis spectrophotometer (Shimadzu 1601, Japan) at 274 nm.Amount of pentoxifylline in the microspheres was estimated with the help of a standard graph.Particle size analysis was carried out using optical microscopy 15 .About 200 microspheres were selected randomly and their size was determined using optical microscope Þ tted with a standard micrometer scale.The surface morphology and the internal textures of microsphers were observed under a scanning electron microscope 16 (Jeol JSM-5610, Japan).FT-IR spectra of pentoxifylline, and poly(є-caprolactone) microsphere loaded with pentoxifylline were taken to check drug polymer interaction and degradation of drug during microencapsulation.

Stability studies:
The microspheres were placed in screw capped glass container and stored at ambient humidity conditions, at room temperatures (27±2 o ), oven temperature (40±2 o ) and in refrigerator (5-8 o ) for a period of 60 d, the microspheres were analyzed for drug content 17 .

In vitro release studies:
The in vitro release profile of pentoxifylline from microspheres was examined in phosphate buffer pH 7.4 using the rotating paddle method (Electro Lab, Mumbai) under sink conditions 18 .Accurately weighed samples of microspheres were added to dissolution   showed highest drug entrapment of 76.92±3.24%w/w.
The FT-IR spectra obtained for pentoxifylline and pentoxifylline-loaded poly(є-caprolactone) microspheres (fig.2).The result indicated that the characteristic peaks due to pure pentoxifylline have appeared in microspheres, without any change in their position after successful encapsulation, indicating no chemical interaction between pentoxifylline and poly(є-caprolactone) and the stability of drug during microencapsulation process.In the stability studies, no appreciable difference was observed in the extent of degradation of products during 60 d in the microspheres which were stored at various temperatures.
The cumulative percent release of pentoxifylline from different formulations is shown in fig. 3.
Pentoxifylline release from all the formulations was slow and sustained over 15 h.The drug release rate

RESULTS AND DISCUSSION
Poly(є-caprolactone) microspheres of pentoxifylline were prepared by solvent evaporation technique.
Poly(є-caprolactone) was selected as a polymer for the preparation of microspheres due to its biodegradable and biocompatible properties.The scanning electron microphotograph of microspheres is shown in fig. 1, it indicated that microspheres were spherical and discrete.The particle size was analyzed by optical microcopy.The particle size differed due to variation in the composition of the formulation.The particle size gradually increased with increasing in the proportion of poly(є-caprolactone).The mean particle size of the microspheres is shown in Table 1.The percentage yield and entrapment efficiency were high for all the formulations and were in the range of 79.63±2.49-83.34±2.46%and 71.96±2.94-76.92±3.24%w/w, respectively, as shown in Table 1.Among the 4 drugs to carrier ratio F 3 showed maximum percentage yield of 83.34±2.46%and F 2 coefÞ cient (r 2 ) was in the range of 0.978-0.987for various formulations as shown in Table 2.When log percentage of drug remaining to be released vs. time was plotted in accordance with Þ rst order equation, straight lines were obtained (r 2 >0.95) indicated that drug release followed Þ rst order kinetics (Þ g. 5).
In present study, an attempt was made to prepare pentoxifylline microspheres using a biodegradable, biocompatible carrier, poly(є-caprolactone) by solvent evaporation technique.The method was found to be simple and reproducible.It may be concluded from the result obtained from evaluation and performance study of microspheres that system may be useful to achieve a controlled drug release proÞ le suitable for peroral administration and may help to reduce the dose of drug, dosing frequency and improve patient compliance.
was decreasing on increasing the polymer ratio.By the end of 15h formulation F 1 , F 2 , F 3 and F 4 released 92.21, 90.34, 76.65 and 63.39% of loaded drug, respectively.The polymer drug ratio 1:4 (F 2 ) showed better drug entrapment and release pattern.It controlled the drug release over 15 h and was found to be the most suitable among other formulations.
The in vitro release data were applied to various kinetics models to predict the drug release mechanism and kinetics.The drug release mechanism from the microspheres was diffusion controlled as plots of the amount released versus square root of time (fig.4) was found to be linear.The correlation

TABLE 1 : YIELD, DRUG ENTRAMENT AND AVERAGE PARTICLE SIZE OF PENTOXIFYLLINE LOADED POLY (Є-CAPROLACTONE) MICROSPHERES
*Average of three preparation ± SD