Hormone-releasing silastic intrauterine devices: effect or provera-releasing intrauterine devices on two species of primates.

Silastic intrauterine contraceptive devices (IUDs) 13 mm long and 1.07 mm in diameter could be inserted easily into patas monkey uteri which, like human uteri, expelled them. Addition of 10% Provera to these devices did not reduce the expulsion rate significantly in our study. Control devices had no effect on cycle length in rhesus monkeys. After insertion, the active IUDs frequently caused a delay in onset of menstruation; however, cycles did occur with the device in situ, and normal-length cycles were resumed following removal of the device. A short period of rapid release (almost 35% of the total amount) of Provera from the device was followed by a longer period of sustained release of low levels of the hormone. Even 9 mug/day were sufficient to maintain a decidual reaction in the endometrium of the rhesus monkey. The drug could not be detected in the blood stream at 3,6, or 12 hours in patas monkeys or at 1 or 2 months in rhesus monkeys and so may never have reached the systemic circulation. Devices currently under study in baboons catain Provera or one of three other steroids to determine whether these compounds improve retention rates as well as meet the other two criteria set for the ideal IUD incorporation, for unless we meet this first criterion we can never achieve, let alone test, the others.