Levonorgestrel as an emergency contraceptive drug

The potential of low-dose levonorgestrel, alone or in combination with ethynyloestradiol (Yuzpe regimen), as emergency contraception is reviewed for its acceptability and effectiveness. Plasma levonorgestrel concentration ranges from 9-12 nmol/l at 12 hours with a peak of 27-33 nmol/l 2-2.5 hours after taking one 0.75 mg tablet. The concentration of steroid hormone binding globulins in plasma is not influenced by the presence of levonorgestrel during this period. The success rates for levonorgestrel-only and the Yuzpe regimen as emergency contraception are 85% and 57%, respectively, while the failure rates are 1.1% and 3.2%, respectively, within the prescribed time limit of use. The mode of action of levonorgestrel emergency contraception is to prevent or delay ovulation and/or alter the endometrium unfavourably the for implantation of an embryo. The use of emergency contraceptive pills within 72 hours after unprotected sexual intercourse reduces the risk of pregnancy by about 75% and is safe, with no serious side-effects.