A randomized trial to compare 24 h versus 12 h double dose regimen of levonorgestrel for emergency contraception

Abstract

Levonorgestrel (0.75 mg given for two doses 12 h apart) has been proven to be an effective regimen for emergency contraception when the first dose is given within 72 h of unprotected coitus. However, the dosing interval is inconvenient for those taking the first dose in the afternoon. We conducted a randomized study to evaluate two levonorgestrel dosing regimens for emergency contraception. Two doses of levonorgestrel 0.75 mg were administered with the first dose given up to 120 h after unprotected intercourse. The second dose was given 12 h later in the first regimen and 24 h later in the second regimen. We conducted a double-blind, randomized trial between 1997 and 2003 at five centres in China. A total of 2071 women requesting emergency contraception within 120 h of unprotected intercourse were recruited. They were randomized to receive two doses of 0.75 mg of levonorgestrel, given either 24 h apart or 12 h apart. Outcome was unknown for 53 women (24 in the 24 h group and 29 in the 12 h group). Among the remaining 2018 women, the crude pregnancy rate was 1.9% in the 24 h group [95% confidence interval (CI) 1.17-2.94] and 2.0% in the 12 h group (95% CI 1.19-2.99). The proportion of pregnancies prevented was estimated to be 72% in the 24 h group and 75% in the 12 h group. Side-effects were mild in both groups. The efficacy of the 12 h regimen declined significantly when there were further acts of intercourse after treatment (5.0 versus 1.0%, P<0.01). This was not observed in the 24 h group. Two doses of 0.75 mg levonorgestrel given either 24 or 12 h apart are effective for emergency contraception up to 120 h after unprotected intercourse. Further research to investigative more effective methods of emergency contraception is warranted.