Some newer progestogens double thromboembolism risk

Women taking oral contraceptives containing drospirenone or desogestrel had twice the risk of venous thromboembolism (VTE) as women taking levonorgestrel pills, a new Danish study found.

The cohort study, which was an expansion of previous work by the researchers, included more than 8 million woman-years of observation from Danish national registries. More than 4,000 first-ever VTE events were included, about two-thirds of them confirmed as certain. The results were published online Oct. 25 by BMJ.

Compared to women not taking hormonal contraception, the relative risk of confirmed VTE was 2.9 for women on ethinylestradiol with levonorgestrel (95% CI, 2.2 to 3.8), 6.4 with drospirenone (95% CI, 5.4 to 7.5), 6.6 with desogestrel (95% CI, 5.6 to 7.8) and 6.2 with gestodene (a progestogen not available in the U.S.). A lower dose of estrogen (20 mg vs. 30 mg) did not reduce VTE risk for women taking drospirenone. When levonorgestrel replaced non-use as a reference standard, the risk of confirmed VTE with the other progestogens was about double. The study found no increase in VTE risk with intrauterine devices or progestogen-only pills.

Based on the sixfold increased VTE risk found to be associated with the hormones, the researchers calculated that the risk of VTE for women on drospirenone, desogestrel or gestodene is 10 per 10,000 woman-years. They noted that 2,000 women would have to switch to levonorgestrel to prevent one VTE in one year.

The author of an accompanying editorial complimented the thoroughness of the study and predicted that many clinicians will choose to minimize risk by prescribing levonorgestrel whenever possible. However, he cautioned that the risk of VTE should not be exaggerated, noting that oral contraceptives are, in general, remarkably safe.