Sustained drug delivery systems II: Factors affecting release rates from poly(epsilon-caprolactone) and related biodegradable polyesters.

The release rates of several steroids from films and capsules of homopolymers and copolymer of epsilon-caprolactone, DL-lactic acid, and glycolic acid were measured in vitro and in vivo for up to 200 days. Relatively constant release rates from capsules (reservoir devices) were observed only under certain conditions. Factors that influence the drug release kinetics were evaluated. Release from poly(epsilon-caprolactone) and poly(epsilon-caprolactone-co-DL-lactic acid) was diffusion controlled. Release from poly(DL-lactic acid-co-glycolic acid) was associated with polymer degradation. Release from poly(DL-lactic acid) was very slow when diffusion controlled.