Controlled Release

The parameters that control the rate of release are the permeability of the polymer membrane, the thickness of the membrane, and the surface area across which the drug diffuses. The easiest way to decrease drug delivery is to decrease the surface area, and this is most readily accomplished by coating the envelope with an incomplete layer of an impermeable polymer. Using this strategy, in addition to Vitrasert® and Retisert®, we have developed intravaginal ring formulations for HIV microbicides, herpes prophylaxis and incontinence.