Levonorgestrel‐Only Dosing Strategies for Emergency Contraception

Abstract

The United States Food and Drug Administration-approved progestin-only dosing strategy for emergency contraception is levonorgestrel 0.75 mg taken as soon as possible within 72 hours of unprotected intercourse, with a second 0.75-mg dose taken 12 hours later. However, different dosing strategies have been studied and promoted by various organizations. The American College of Obstetricians and Gynecologists recommends a single dose of levonorgestrel 1.5 mg for emergency contraception as one option. As another option, they recommend two doses of levonorgestrel 0.75 mg may be effective when taken 12-24 hours apart. We performed a search of MEDLINE and International Pharmaceutical Abstracts from 1967-2006 to evaluate and describe the existing pharmacokinetic and patient outcome data regarding administration of levonorgestrel as a 1.5-mg single dose or two 0.75-mg doses taken 12 or 24 hours apart. Additional studies were identified from the bibliographies of the selected literature. Several pertinent articles were identified. All of the studies demonstrated that emergency contraception effectively prevented pregnancy. In addition, evidence supports the safety and efficacy of a single dose of levonorgestrel 1.5 mg for emergency contraception. Furthermore, when two doses of levonorgestrel 0.75 mg are administered, the second dose can confidently be taken 12-24 hours after the first without compromising efficacy. Understanding the evidence that supports the different emergency contraception dosing strategies is critical for clinicians, and especially pharmacists, who have interactive roles in dispensing emergency contraception.