Controlled release of beta-estradiol from biodegradable microparticles within a silicone matrix

Novel, biodegradable controlled release systems were prepared from biodegradable microparticles of poly(lactic acid-co-glycolic acid) containing beta-estradiol in the presence or absence of silicone. The release behavior of beta-estradiol from free microparticles as well as from microparticles embedded within a silicone matrix was compared with the release behavior shown by nonencapsulated beta-estradiol within a silicone matrix. It was found that incorporating biodegradable microparticles within a silicone matrix lessens the initial burst of release often seen with these types of formulations and provides a controlled rate of drug release. In addition, the release rate of beta-estradiol from biodegradable microparticles within silicone is higher than for unencapsulated beta-estradiol in silicone. This type of formulation may be useful in a number of instances such as release of drugs from implants for which a simple drug-silicone formulation does not yield desired release behavior, formulations which are currently developed for microparticles but which may need to be removed if necessary, and implant formulations containing drugs which will not diffuse through silicone.