OBJECTIVE:

Compare the efficacy and adverse effects of CDB-2914, a new progesterone receptor modulator, to levonorgestrel for emergency contraception.

METHODS:

We performed a randomized, double-blinded noninferiority trial, enrolling healthy women seeking emergency contraception within 72 hours of unprotected intercourse. Participants were randomly assigned to receive a single dose of 50 mg of CDB-2914, plus a placebo 12 hours later or two doses of 0.75 mg of levonorgestrel taken 12 hours apart. Follow-up was scheduled 5 to 7 days after the expected onset of the next menstrual period. Posttreatment pregnancy was established by a positive urine test at follow-up and confirmed by quantitative serum beta-hCG. Daily diaries were used from the time of emergency contraception use until next menses to record adverse effects and sexual activity.

RESULTS:

Product efficacy was evaluable in 775 of CDB-2914 users and 774 of levonorgestrel users. Pregnancies occurred in 7 (0.9%, 95% confidence interval 0.2-1.6%) and 13 (1.7%, 95% confidence interval 0.8-2.6%) women, respectively. Based on the estimated cycle day of unprotected intercourse, 85% and 69% of anticipated pregnancies, respectively, were averted. Nausea was reported by a somewhat greater percentage of CDB-2914 than levonorgestrel users (29% compared with 24%, P=.03), but the distribution of other adverse effects was similar in both groups. Women in both groups experienced considerable variation in menstrual cycle length as compared with their reported individual normal cycle lengths.

CONCLUSION:

CDB-2914 is at least as effective as levonorgestrel in preventing pregnancies after unprotected intercourse and has a similar side effect profile.

LEVEL OF EVIDENCE:

I.

TRIAL REGISTRATION:

ClinicalTrials.gov NCT00271583.