PubMed · 15006303
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Anne M C Webb. 2004. Emergency contraception: latest changes.. https://doi.org/10.1783/147118904322701866
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OBJECTIVES: To investigate the effect of a single low dose of mifepristone on ovarian function, when administered in the preovulatory period. METHODS: Healthy women with regular menstrual cycles were studied during two consecutive menstrual cycles. Either mifepristone or placebo was given in a randomized double-blind order when the leading follicle reached a diameter between 15 and 17 mm. Daily ultrasound and serum hormone measurements were obtained until follicular collapse. Statistical analysis was performed using Wilcoxon signed-rank test. RESULTS: Eight women entered the study, although one woman had to be excluded afterwards from analysis because her LH surge had already appeared on the day of treatment. The LH surge was delayed from day 14 to 17 (P = 0.01). Mifepristone caused a 3-day delay in follicular collapse, occurring on day 16 in control cycles and on day 19 in mifepristone treatment cycles (P = 0.02). The median cycle length was 26 days in control cycles and 30 days in mifepristone treatment cycles (P = 0.03). Progesterone measurement 7 days after follicular collapse did not differ significantly between both cycles. CONCLUSIONS: A single 10-mg dose of mifepristone administered during the preovulatory phase of the cycle delays the LH surge and postpones ovulation.
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The potential of mifepristone to be an emergency contraceptive is reviewed. Mifepristone prevents 92-100% of pregnancies with an acceptable side-effect profile on oral intake of a 10-600-mg dose within 72 h of unprotected intercourse. A single dose of 10 mg mifepristone resulted in a pregnancy rate of 1.5%, similar to a 1.5-mg single dose or two doses of 0.75 mg levonorgestrel 12 h apart, administered within 120 h (current standard) of unprotected sexual intercourse. Mifepristone and levonorgestrel do not differ in efficacy as emergency contraceptives. The mode of action of emergency contraception (EC) with mifepristone or levonorgestrel is primarily associated with inhibition of ovulation rather than prevention of implantation. Different doses of mifepristone appear to have similar effects. However, delay in the onset of subsequent menstruation caused by mifepristone is dose dependent and is reduced with a lower dose without affecting its efficacy. Patient acceptability of mifepristone as EC is high. However, the optimum standard dose of mifepristone is yet to be established for its application as an effective and acceptable emergency contraceptive drug for ordinary clinical use or practice.