Using menstrual data to time the administration of mifepristone as
once-a-month contraceptive pill
N. Narvekar (1), P.C. Ho (2), L. Cheng (3), Z.V.D. Spuy (4), K. Dada
(5), A. Glasier (1), D.T. Baird (1)
Contraceptive Development Network, Edinburgh, Scotland, UK (1); Department
of Obstetrics and Gynaecology, University of Hong Kong, Hong Kong (2); Shanghai
Institute of Family Planning Technical Instruction, Shanghai (3); Department of
Obstetrics and Gynaecology, University of Cape Town , South Africa (4); Centre
for Research in Reproductive Health, Sagamu, Nigeria (5)
Introduction: Many women find the idea of a once-a-month contraceptive
pill attractive. Mifepristone has been shown to be an effective once-a-month
contraceptive if administered orally in the early luteal phase of the cycle.
However unless mifepristone is given within 3 days of ovulation there is
widespread disruption in the pattern of menstrual bleeding.
Aims and Methods: In this study we tested the feasibility of timing
the administration of mifepristone on the 12th day before next menses as
calculated from the length of the three previous menstrual cycles. 399 women in
5 centres (Edinburgh, Capetown, Sagamu, Hon Kong, Shanghai) were randomised to
receive 10, 25 or 200 mg of mifepristone or placebo.
Results: The menstrual period came within 5 days of the predicted date
in 88% of women receiving placebo, 84% of women receiving 10 mg, 72% of women
receiving 25 mg and only 48% of women treated with 200 mg of mifepristone.
Increasing dose of mifepristone was associated with an increasing chance of
having a detailed period p<0.001 with 3, 10, 18 and 26% of women in the placebo, 10, 25 and 200 mg groups respectively having a delay in onset of menses of more than 5 days. Only 45% of women were in the peri-ovulatory phase of the cycle according to LH and progesterone measurements on the day of drug administration. Women treated before ovulation were more likely to have delayed menses with all three doses of mifepristone. Only women treated with 200 mg of mifepristone were likely to have an early period if treated after ovulation.
Conclusions: It seems unlikely that mifepristone administered once a
month at a time based on the calendar would provide a reliable method of
contraception.
