Formulation of delivery systems with risperidone based on biodegradable terpolymers.

Risperidone is applied in oral dosage formulations in the treatment of mental diseases. Current trends point toward parenteral delivery systems based on poly(lactide-co-glycolide), with wafers or rods being the more attractive option than the routinely used intramuscular suspension with microparticles. The aim of our work was to study the utility of solution casting and hot melt extrusion in the formulation of wafers and rods with risperidone based on terpolymers, namely poly(lactide-co-glycolide-co-trimethylene carbonate) and poly(lactide-co-glycolide-co-ε-caprolactone). Synthesis of the terpolymers was carried out by using a non-toxic zirconium initiator and a racemic (LL/DD) or optically active form of the lactide monomer. The delivery systems were analyzed by NMR, DSC, GPC, and SEM. The release profile was monitored by HPLC. Terpolymer chain microstructure, glass transition temperature, and morphology revealed unchanged values after formulation. Solution casting resulted in a drop in molecular weight to a smaller degree than hot melt extrusion. The presence of risperidone influenced another decrease in molecular weight. Both methods are adequate for the formulation of delivery systems based on terpolymers for prolonged release of risperidone. An adequate selection of monomer composition in terpolymers allows to control the release period. Risperidone was released in three phases, however, the burst effect was observed for poly(L-lactide-co-glycolide-co-ε-caprolactone).