BIODEGRADABLE CONTROLLED-RELEASE TABLETS .3. EFFECT OF POLYMER CHARACTERISTICS ON DRUG-RELEASE FROM HETEROGENEOUS POLY(LACTIDE-CO-GLYCOLIDE) MATRICES

Spray dried poly(lactide-co-glycolide) powders were used to prepare phenobarbitone matrix tablets. The release of phenobarbitone was significantly sustained, indicating the suitability of using poly(lactide-co-glycolide) matrix tablets for long-term controlled drug delivery. Drug release profiles consisted of three regions: these were an initial region of relatively high release rate (burst effect), followed by an extended region of lower and essentially constant release rate from approx. 20 to 80% of drug release. This steady state release region was followed by a final one in which the rate of drug release fell off as exhaustion of the drug in the matrix approached. A composite mechanism of drug release is proposed involving diffusion of the drug through water-filled pores in the matrix and drug diffusion through the swollen polymer. The rate of drug release increased with an increase in the glycolide content of the polymers. Decreasing the polymer molecular weight caused initially an increase but later a decrease in the release rate. These results are discussed in terms of degradation, water uptake and swelling of the polymers upon immersion in aqueous media.