IN-VITRO CONTROLLED-RELEASE KINETICS OF LOCAL-ANESTHETICS FROM POLY(D, L-LACTIDE) AND POLY(LACTIDE-CO-GLYCOLIDE) MICROSPHERES

Poly(D, L)lactide and polylactide-co-glycolide drug-loaded microsphere s were prepared with lipophilic (bupivacaine and etidocaine) and hydro philic (mepivacaine and lidocaine) local anaesthetics. Formulations of drug-loaded microspheres were characterized by the drug content, the in-vitro release kinetics and by the physical state of the drug within the microspheres. Release rates of the local anaesthetics from the mi crospheres were different and could not be accounted for by the intrin sic dissolution rates of the drugs. The encapsulation efficiency was h ighly dependent on the lipophilicity of the drugs, reaching the maximu m for the lipophilic drugs and the poly(lactide-co-glycolide) polymers . The influence of the molecular weight of the poly(lactide-co-glycoli de) polymers on the release rate and on the release mechanism depended on the drug studied and its physical state within the polymeric matri ces. Diffusion-controlled release was evidenced in various formulation s as a result of the linearity of the release as a function of the squ are root of time.