Plasma levels of norethindrone and effect upon ovarian function during treatment with silastic implants containing norethindrone
Odlind, V.; Weiner, E.; Johansson, E.D.
Contraception 19(2): 197-206
1979
ISSN/ISBN: 0010-7824 PMID: 428235 DOI: 10.1016/s0010-7824(79)80032-3Document Number: 442394
The effect on the ovarian steroid pattern of treatment with s.c. implanted silastic rods containing norethindrone was evaluated. Four rods, each containing 37 mg norethindrone (NET), were implanted s.c. in 5 women and left in place for 135-200 days. Plasma levels of NET, estradiol and progesterone were determined by radioimmunoassays. After an initial peak found in all subjects, the plasma level of NET declined. Great day-to-day variations of NET were found. Ovulations were suppressed during treatment in 3 subjects. One subject had regular ovulations throughout treatment and in 1 subject a single ovulation was recorded. Peaks of estradiol without subsequent ovulation were found in 2 subjects. The bleeding pattern was irregular; 3 subjects had varying degrees of spotting and bleeding, 2 subjects were amenorrheic. The average daily release rate was 300 .mu.g, calculated from the amount of steroids lost from the removed rods. The release of steroid from 4 NET rods is high enough only initially to completely inhibit ovulation.