Meta-analyses of randomized trials comparing different doses of mifepristone in emergency contraception

Abstract

There is some evidence from randomized trials that different doses of mifepristone for emergency contraception do not differ in efficacy in the range from 10 mg to 600 mg. Lower doses have a better side effect profile and are cheaper and therefore they would be preferable in the absence of a dose effect. However, the lack of significance is not evidence of absence of an effect. More evidence can be obtained by combining results of trials. We present meta-analyses of randomized trials comparing doses of mifepristone for emergency contraception from 5 mg to 600 mg, with regard to the efficacy to prevent unwanted pregnancies. We use two approaches for analysis, one using only within-trial information and another one combining within-trial with between-trial information. We discuss the results in terms of equivalence. There is some evidence of a small dose effect on efficacy in the lower range of doses (<50 mg). The pregnancy rate increases by a factor of 1.6 when the dose of 10 mg is used instead of 25 mg (95% confidence interval: 1.1-2.4). In terms of the number of women needed to treat, however, using 10 mg in the place of 25 mg implies having one extra pregnancy every 146 women requesting emergency contraception, which might be a low cost compared to the benefit of more women having access to treatment.