Mifepristone tied to bleeding with progesterone-only IUS.

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 [levonorgestrel intrauterine system]," 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. It has been suggested that this effect may be due to mifepristone's functional inhibition of progesterone, which leads to the upregulation of endometrial estrogen receptors, she said at the joint annual meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society.

But Dr. Econimidis' study found that, when given to 20 regularly menstruating women who were new starters of the LNG-IUS, mifepristone actually had the opposite effect. "The local effect of the levonorgestrel on the endometrium may be triggering bleeding ... [and] may not be allowing the mifepristone to act on the endometrium," she said in an interview. "In women who are on a progesterone-only implant or injectable, that mechanism, in terms of concentration of levonorgestrel ...