Contraceptive Patch More Likely Than Pill to Cause Venous Thromboembolism

NEW YORK (Reuters Health) Feb 19 - Women who use a transdermal contraceptive system are more than twice as likely to develop venous thromboembolism as those who use an oral contraceptive, new research shows.

Due to the rarity of events, the researchers were unable to determine if use of the contraceptive patch increases the risk of MI and stroke, according to the report in the February issue of Obstetrics and Gynecology.

The study involved 49,048 women who used the norelgestromin/ethinyl estradiol patch (Ortho Evra) and 202,344 who used norgestimate-containing oral contraceptives with ethinyl estradiol between April 2002 and December 2004.

Dr. Alexander M. Walker and colleagues, from i3 Drug Safety in Auburndale, Massachusetts, note that at the study's inception, it was not known if users of the transdermal system ran the same risk of stroke, MI and venous thromboembolism as users of oral contraceptives. They do point out that the FDA changed the labeling in 2005 to warn of a possible increased risk of thrombotic events because of a higher average circulating estrogen level with the transdermal contraceptive system.

The researchers found that the venous thromboembolism rate in patch users was 2.2-times higher than in pill users: 40.8 vs. 18.3 cases per 100,000 woman-years. In a nested case-control analysis, which excluded high-risk factors, the risk was elevated 2.4-fold.

Three patch users and seven pill users experienced a myocardial infarction, a difference that wasn't statistically significant. No patch users experienced a stroke, but 10 pill users did, the investigators report.

Obstet Gynecol 2007;109:339-346.