Polymeric compositions useful as controlled release implants

A thermoplastic polymer system suitable as a controlled release implant, comprising:

• a solid, microporous matrix of a pharmaceutically acceptable, biodegradable thermoplastic polymer which is insoluble in aqueous medium or human or animal body fluids, a biologically active agent, and up to about 15% by weight of a pharmaceutically acceptable, water-insoluble, rate-retarding agent which retards the rate of release of the biologically active agent from the matrix up to 100 fold relative to its rate of release from the same matrix without the rate-retarding agent, and which imparts a Tg to the matrix of less than about 55.degree. C., the weight being relative to the total weight of the matrix;
• and,
• the microporous matrix being formed externally or in situ respectively by a process comprising combining a composition with the aqueous medium, or administering the composition directly into a body tissue or cavity having the human or animal body fluids;
• the composition comprising the thermoplastic polymer, the biologically active agent, the rate-retarding agent and a pharmaceutically acceptable organic solvent in which the thermoplastic polymer, biologically active agent and rate-retarding agent are dissolved or dispersed, the organic solvent being miscible to dispersible in aqueous medium or human or animal body fluids;
• the combining step or administering step resulting in diffusion of the organic solvent into the aqueous medium or body fluid and resulting in coagulation of the thermoplastic polymer to form the solid microporous matrix;
• the thermoplastic polymer being selected from the group consisting of polylactides, polyglycolides, polycaprolactones, polyanhydrides, polyamides, polyurethanes, polyesteramides, polyothoesters, polydioxanones, polyacetals, polyketals, polycarbonates, polyorthocarbonates, polyphosphazenes, polyhydroxybutyrates, polyhydroxyvalerates, polyalkylene oxalates, polyalkylene succinates, poly(malic acid), poly(amino acids), and copolymers, terpolymers and any combination thereof, and the thermoplastic polymer having a molecular weight up to about 0.8 inherent viscosity;
• and,
• the rate-retarding agent being selected from the group consisting of an ester of a mono, di or tricarboxylic acid, a polyhydroxy alcohol, a fatty acid, a fatty acid ester, an epoxidized oil, a sterol, a higher alkyl alcohol, and any mixture thereof.