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Population-based evaluation of two regimens for emergency contraception : a pharmacoepidemiologic study

University of British Columbia

The Yuzpe (YZP) and levonorgestrel (LNG) emergency contraceptive (EC) regimens can prevent pregnancy after unprotected intercourse (UPI). This investigation was aimed at measuring EC users' pregnancy rates under routine clinical conditions, comparing the effectiveness of the two regimens, reporting effectiveness using informative effect measures, and evaluating the impact of the timing of receiving ECs on the pregnancy rate. This cohort study included women who received pharmacist-prescribed ECs within a 25-month period. Treatment consent forms were matched to prescription records, which were linked to community and hospital medical records, to identify pregnancy-related administrative codes. Three experts adjudicated the data for time-compatible outcomes, and an observed pregnancy rate was determined for each regimen. The regimens were compared using logistic regression modeling, with adjustment for covariates. To evaluate EC effectiveness, observed pregnancy rates were compared against estimated expected pregnancy rates. The impact of EC timing was assessed by estimating the absolute risk reduction over time, and with logistic regression. Among 7493 women in the cohort, there were 99 (2.2%) and 94 (3.1%) compatible pregnancies in the LNG and YZP groups, respectively (p = 0.02). The crude odds ratio of pregnancy (LNG vs. YZP) was 0.71 (95% CI: 0.53 to 0.94). The adjusted odds ratio was ~0.65 (95% CI: 0.48 to 0.89) in the main analysis and sensitivity analyses. The expected pregnancy rate was ~4.1% in both groups. For LNG, the relative and absolute risk reductions were 47.6% and 2.0%, respectively [number needed to treat (NNT) = 50]. For YZP, the relative and absolute risk reductions were 24.4% and 1.0%, respectively (NNT = 100). Absolute risk reductions in the combined cohort decreased from 2% for EC dispensed within 24 hours to <1% beyond 72 hours after UPI. The adjusted odds of pregnancy increased by 1.27 (95% CI: 1.04-1.57) for each additional day after UPI. In conclusion, the LNG regimen was found to be superior to the YZP regimen for preventing pregnancy in routine clinical use. Given the limited effectiveness and treatment timeframe of these oral ECs, alternative forms of EC and regular contraception should be considered, and personalized according to each woman's preferences.

Text

2012-10-18

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/43487

Pharmaceutical Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/