A new biodegradable implant consisting of waxy-type poly(ε-caprolactone-co-δ-valerolactone) and estramustine

Abstract

Abstract Biodegradable waxy-type copolyesters were prepared by direct copolycondensation of e-caprolactone (CL) and δ-valerolactone (VL) in the absence of catalysts, to apply as implantable matrices for drug delivery systems. The copolyesters are much more subject to erosion than their homopolyesters, in which the degradation is further accelerated by the action of lipase-type enzyme. Estramustine was incorporated into a small cylinder of waxy-type poly(CL-co-VL) with 92 mol% CL unit device by the so-called melt-pressing technique. The in vivo capability of this device was evaluated by implanting into the back of male rats. The drug release, although accompanying a burst phenomenon in the initial stage, was kept constant throughout an experimental period of 19 weeks from the 1st to 20th week. In this case, the release pattern was parallel to the degradation pattern, in support of the release being the rate-limiting step in the degradation of the polymer. The results showed about 75% of the initial drug content was still present in the device even after 20 weeks implantation. This finding means that the biodegradable poly(CL-co-VL) wax is very useful as an implantable matrix for a drug delivery system which controls the release over a relatively long period of time.