Preparation and evaluation of microcapsules containing diclofenac sodium and Eudragit RS or RL as oral sustained release multiparticulte delivery system

Microencapsulation is a well-known method that is used to modify and retard drug release. In this study, the preparation of diclofenac sodium and Eudragit RS and/ or RL microcapsules was accomplished in order to asses the suitability of them for production of oral sustained release multiparticulate dosage form of diclofenac sodium. Microcapsules were prepared using the emulsion solvent evaporation method. The effect of formulation variables namely polymer:drug ratio, type of polymer and inclusion of PEG 400 as a channeling agent were investigated on shape and surface characteristics of microcapsules (by scanning electron microscopy), percentage yield and drug entrapment efficiency, mean particle size (sieve analysis) and drug release profiles (dissolution test). Microscopic examination of microcapsules revealed that all microcapsules were well-shaped and nearly spherical. Percentage yield was more than 90% and drug entrapment efficiency was more than 95% for most of the cases and therefore confirmed the suitability of the method for production of microcapsules with high drug loading. The mean particle size for different microcapsules was in the range of 390 - 589 μm. Drug release was very slow from microcapsules with 3:1 polymer: drug ratio. Increase in stirring speed did not influence the size and release characteristics of microcapsules at 3:1 polymer: drug ratio. Decrease in polymer:drug ratio to 2:1 did not significantly influence the release rate of drug. Further decrease in polymer: drug ratio to 1:1 increased the rate of drug release. However drug release from all formulations was incomplete at the end of dissolution test. Despite the higher water permeability of Eudragit RL both Eudragit types behaved similarly in controlling drug release rate. This observation and also incomplete drug release from all microcapsules were attributed to the probable electrostatic interaction between cationic quaternary ammonium groups in Eudragit RS and RL and diclofenac sodium.The inclusion of 10 or 20% PEG 400 in microcapsule wall resulted in microcapsules with very smooth surface and increased the rate of drug release. Calculation of difference factor revealed that the release profile of microcapsules with 1:1 polymer: drug ratio and containing 10% PEG was similar to commercial sustained release pellets of diclofenac sodium (Modafen). The emulsion solvent evaporation method was successful in production of diclofenac sodium and Eudragit RS or RL microcapsules. The yields of preparation and drug entrapment efficiencies were high for all microcapsules obtained. The drug: polymer ratio and inclusion of PEG 400 influenced the in vitro drug release; however the microencapsulation yield and drug entrapment efficiency were not influenced. The 1:1 polymer: drug ratio produced better release profile for oral drug delivery.