MONTREAL — Contrary to its effect with other progesterone-only contraceptives, mifepristone increases breakthrough bleeding in patients using the levonorgestrel intrauterine system, according to a new study.
“Mifespristone cannot be recommended as a therapy for breakthrough bleeding in new users of the LNG-IUS,” reported Dr. Megan Econimidis of the Keck School of Medicine at the University of Southern California in Los Angeles.
Mifepristone, an antiprogesterone, has been shown to decrease irregular bleeding in users of progesterone-only implants and injectables. But when given to 20 regularly menstruating women who were new starters of the LNG-IUS, mifepristone actually had the opposite of its usual effect, she said at the joint annual meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society.
The women in the study, 18–45 years old, were randomized to receive mifepristone 50 mg or placebo every 2 weeks for six cycles. The treatment was started 2 weeks after LNG-IUS insertion.
Over the six cycles, the median number of days of breakthrough bleeding was 57 in the mifepristone group, compared with 26 in the placebo group; this difference was statistically significant. In addition, when all the subjects' cycles were combined, there were 22 (42%) mifepristone cycles with more than 8 days of breakthrough bleeding vs. 16 (27%) placebo cycles. This difference was not statistically significant.
Endometrial biopsies showed a decrease in endometrial estrogen receptors after mifepristone treatment. This is in contrast to other studies of progesterone implants and injectables, which have shown an increase in estrogen receptors with mifepristone treatment, she said.