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Obstetrics & Gynecology 2007;110:587-593
© 2007 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Risk of Thromboembolism in Women Taking Ethinylestradiol/Drospirenone and Other Oral Contraceptives

John D. Seeger, PharmD, DrPH1,2, Jeanne Loughlin, MS1, P. Mona Eng, ScD1, C. Robin Clifford, MS1, Jennifer Cutone, MPH, MBA1 and Alexander M. Walker, MD, DrPH1,2

From 1i3 Drug Safety, Ingenix, Waltham, Massachusetts; and 2Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts.

OBJECTIVE: The oral contraceptive ethinylestradiol 0.03 mg/drospirenone 3 mg contains a progestin component that differs from other oral contraceptives. Case reports and prescription event monitoring suggested that ethinylestradiol/drospirenone might be associated with an elevated risk of thromboembolism. We sought to estimate the association between ethinylestradiol/drospirenone and risk of thromboembolism relative to the association among other oral contraceptives.

METHODS: We identified ethinylestradiol/drospirenone initiators and a twofold larger group of other oral contraceptive initiators between June 2001 and June 2004 within a U.S. health insurer database. The comparison group was selected to have demographic and health care characteristics preceding oral contraceptive initiation that were similar to ethinylestradiol/drospirenone initiators. Thromboembolism during the follow-up of the cohorts was identified through claims for medical services, and only medical record–confirmed cases were included in analyses. The primary (as-matched) analysis used proportional hazards regression, whereas a secondary (as-treated) analysis accounted for changes in oral contraceptives during follow-up using Poisson regression.

RESULTS: The 22,429 ethinylestradiol/drospirenone initiators and 44,858 other oral contraceptive initiators were followed for an average of 7.6 months, and there were 18 cases of thromboembolism in ethinylestradiol/drospirenone initiators and 39 in the comparators (rate ratio 0.9, 95% confidence interval 0.5–1.6). More than 9,000 women would need to be prescribed oral contraceptives to observe a difference of one case of thromboembolism. Results of the as-treated analysis were similar to those of the as-matched analysis.

CONCLUSION: Ethinylestradiol/drospirenone initiators and initiators of other oral contraceptives are similarly likely to experience thromboembolism.

LEVEL OF EVIDENCE: II






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