Abstract

PIP: Serum level of dl-norgestrel (dl-Ng) were measured by a special radioimmunoassay method after oral and intravaginal administration. 3 women received .075 mg/day dl-Ng orally for 5 days, and 3 others received 50 or 100 mg dl-Ng via a polysiloxane elastomer placed in the vagina for 3 weeks. The radioimmunoassay method proved to be highly effective; cross reacting with less than .01% 1-Ng. Circulating levels of dl-Ng were detectable 30 minutes after oral ingestion, and reached peak values of 2, 1.7 and 1.5 ng/ml in 1 and 2-3 hours, respectively. Serum levels fell rapidly thereafter, reaching levels of .2-.4 ng/ml within 24 hours after injection. Serum dl-Ng levels rose rapidly after insertion of the intravaginal device, and reached peak values of 5 ng/ml and 7-11 ng/ml with 50 and 100 mg dl-Ng, respectively, within 24-48 hours after insertion. Serum dl-Ng levels then declined to about 30-40% of initial treatment concentrations. During subsequent cycles, serum dl-Ng levels remained relatively constant at 1-3 ng/ml. Concentrations declined rapidly to .2 ng/ml within 5-7 days after removal of the device. Preovulatory patterns of estradiol were observed, but ovulation did not occur, as evidenced by low progesterone values. During the 1st and 2nd treatment cycles, withdrawal bleeding began at times ranging from the day of removal to 5 days after removal. In the later treatment cycles, withdrawal bleeding began prior to removal of the device. The results indicate that the more constant release of dl-Ng with the intravaginal ring provides better control of irregular bleeding than orally administered dl-Ng.