Mifepristone eyed for emergency contraception
While American providers have just begun to use mifepristone for early medical abortion, researchers are looking at the drug’s possible use in emergency contraception.
Investigators coordinated by the Geneva-based World Health Organization (WHO) Special Programme of Research, Development, and Research Training in Human Reproduction compared the effectiveness and side effects, including the timing of the next menstrual period, of three dosages of mifepristone given within five days of unprotected intercourse.1
"We carried out this three-dose study to investigate, in comparison to the 600-mg dose, the clinical efficacy of the 50-mg and 10-mg doses in emergency contraception," notes Helena von Hertzen, MD, medical director of the Special Programme of Research, Development, and Research Training in Human Reproduction. "As there was no significant difference in the efficacy of these doses, we are continuing research with the 10 mg dose."
Recruitment for the study was scheduled to continue until the end of 2000, and it should come close to its original recruitment target of 4,150 women, says von Hertzen. Scientists plan to carry out the final analysis in early March and publish the results soon thereafter, she reports.
Two previous studies carried out in collaboration with investigators in the United Kingdom using a 600-mg dose of mifepristone suggested that mifepristone could be more effective and cause fewer side effects than the Yuzpe regimen of emergency contraception, notes von Hertzen.2,3 The Yuzpe regimen requires two doses of 100 mg each of ethinyl estradiol plus 500 mg of levonorgestrel given 12 hours apart within 72 hours of unprotected intercourse.
Research also has indicated that mifepristone administered prior to ovulation can block ovulation or shift it to a later date, says von Hertzen. On the other hand, if ovulation already has occurred, the compound delays the development of the endometrium, she points out.
To look at the use of mifepristone in emergency contraception, the WHO designed a multicenter, single-masked, randomized trial in 11 family-planning clinics in Australia, China, Finland, Georgia, United Kingdom, and the United States. More than 1,700 healthy women with regular menstrual cycles who requested emergency contraception within 120 hours of unprotected intercourse were randomly assigned to three treatment groups, using 600 mg, 50 mg, or 10 mg of mifepristone.
Lowering the dose of mifepristone 60-fold did not decrease its effectiveness as an emergency contraceptive under typical use, researchers found. The researchers concluded that the lowest dosage of mifepristone is as effective in preventing pregnancy as the larger dosages, making it a more affordable choice. The smaller dosage also resulted in the lowest incidence of side effects, particularly delay in onset of the next menses.
While mifepristone appears to be safe, highly effective, and acceptable for use in emergency contraception, it may be some time before it is used in the United States in this particular context, observes Carolyn Westhoff, MD, professor of obstetrics, gynecology, and public health at Columbia University in New York City. Westhoff has participated in several of the mifepristone trials for use of the drug in medical abortion.
"Everyone who is interested, from clinicians, to companies, to activists, all have their hands very full with the tasks of getting both the two branded emergency contraceptive pills and Mifeprex [the brand name for the U.S.-approved mifepristone] itself integrated into the U.S. clinical world," ex-plains Westhoff. Shipments of mifepristone for use in U.S. medical abortion began in November 2000 by New York City-based Danco Laboratories. (Contraceptive Technology Update will provide an update on mifepristone’s introduction in an upcoming issue of the newsletter.)
Continue to counsel women that mifepristone is approved in the United States for use in medical abortion. Refer to the January 2001 issue of CTU for guidance in discussing the difference between Mifeprex and emergency contraceptive pills. (For more on mifepristone, see Contraceptive Technology Reports in this issue.)
References
1. Task Force on Postovulatory Methods of Fertility Regulation. Comparison of three single doses of mifepristone as emergency contraception: A randomised trial. Lancet 1999; 353:697-702.
2. Glasier A, Thong KJ, Dewar M, et al. Mifepristone (RU 486) compared with high-dose estrogen and progestogen for emergency postcoital contraception. N Engl J Med 1992; 327:1,041-1,044.
3. Webb AM, Russell J, Elstein M. Comparison of Yuzpe regimen, danazol, and mifepristone (RU486) in oral postcoital contraception. BMJ 1992; 305:927-931.
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