Drospirenone: high risk of venous thrombosis

Oral contraceptives increase the risk of venous thrombosis, with the extent depending on the dose of ethinylestradiol and the type of progestin: the risk is about 20 cases per 100,000 woman-years with norethisterone or levonorgestrel and less than 50 microgrammes of ethinylestradiol, and 30 to 40 cases per 100,000 woman-years with gestodene or desogestrel. Since the beginning of this decade, some oral contraceptives have combined ethinylestradiol with drospirenone, a spironolactone-derived progestin with antimineralocorticoid activity, which carries a risk of hyperkalaemia. A Danish cohort study was based on a registry containing 3.3 million woman-years of data on oral contraceptives, including more than 130,000 woman-years of drospirenone exposure. Compared with levonorgestrel, a statistically significant increase in the risk of venous thrombosis was observed in women using drospirenone (relative risk 1.64, 95% confidence interval 1.27-2.10). A case-control study conducted in the Netherlands that included 1524 patients and 1760 controls showed a statistically significant 6-fold increase in the risk of thrombosis among women using combinations containing drospirenone compared to women who did not use oral contraception, and a non-significant 1.7-fold increase compared to women using combinations based on levonorgestrel. In practice, the first-choice combined oral contraceptives are those containing ethinylestradiol plus either levonorgestrel or norethisterone.