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 ph enobarbitone matrix tablets. The release of phenobarbitone was signifi cantly 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 re gion of relatively high release rate (burst effect), followed by an ex tended region of lower and essentially constant release rate from appr ox. 20 to 80% of drug release. This steady state release region was fo llowed by a final one in which the rate of drug release fell off as ex haustion of the drug in the matrix approached. A composite mechanism o f drug release is proposed involving diffusion of the drug through wat er-filled pores in the matrix and drug diffusion through the swollen p olymer. The rate of drug release increased with an increase in the gly colide content of the polymers. Decreasing the polymer molecular weigh t caused initially an increase but later a decrease in the release rat e. These results are discussed in terms of degradation, water uptake a nd swelling of the polymers upon immersion in aqueous media.