Biodegradable systems for the sustained release of fertility-regulating agents.

Biodegradable delivery systems constitute the most recent approach to prolong the duration of action of steroids used for the control of female as well as male fertility. Erodible systems are smaller than non-biodegradable devices and. if prepared in the form of microparticles, can be injected through regular needles. On the other hand, since their components diffuse into the systemic circulation, they require careful long-term toxicological evaluation of all hydrolysis products. Release of the active drug from biodegradable systems is achieved through various mechanisms such as erosion, diffusion, a combination of the two and cleavage of a covalent linkage between the drug and the polymer matrix. Systems under development at present include devices made of poly-lactic and/or poly-glycolic acid, and of polymers made from ϵ-caprolactone. In addition other polymers such as poly-orthoesters have been used. Finally, experiments are in progress using poly-glutamic acid to which steroids are covalently bound.