Preparation and pharmacokinetic evaluation of a modified long-acting injectable norethisterone microsphere.

Prototype long-acting formulations of norethisterone in the form of injectable microspheres made of biodegradable co-polymer of polylactic acid and glycolic acid have been successfully used as injectable contraceptives in women. Second-generation formulations with improved in vitro and in vivo norethisterone-release profiles have been developed and tested in baboons. A cyclic pattern of norethisterone release has been achieved by modification of the surface properties of the prototype formulation. One such modification, and the resulting effects on the in vitro and in vivo norethisterone release profiles will be presented and discussed.