Differential effects of progestins on hemostasis.

Recently large, prospective, randomized studies on hormone replacement therapy (HRT) have indicated that the progestin use might interfere with hemostasis and thus increase venous thrombotic events. Therefore, available publications were evaluated to determine whether progestins interfere with hemostasis, either when given alone via oral or parenteral routes or in combination with ethinylestradiol as synthetic estrogen or natural estrogens. There are indications that such interference is dependent upon the type and dose of the progestin, the route of application, the length of treatment and the type and dose of the estrogen with which it is combined. For natural progesterone, no negative effects on the hemostatic system were seen with either oral or parenteral application, in cyclic or continuous regimens, for the doses investigated. Similarly, no unwanted effects were seen with progestin only pills (POP), independent of the type and dose of progestin, or parenteral progestins. With the high-dose progestins used in gynaecological oncology, the increased activation of the hemostatic system resulting from the disease itself has to be taken into account when looking at any increased incidence of thromboembolic events in these patients. For estrogen/progestin combinations, the risk of venous thromboembolism is attributed to the estrogen used. Recent studies showed an increased rate of thromboembolic events in association with desogestrel-and gestodene-containing oral contraceptives, compared with those containing levonorgestrel. With HRT, a decrease in antithrombin factors could explain the increased rate of venous thrombotic events. In conclusion, progestins seems to have different effects on the hemostatic system due to their different pattern of biological activities. This was also shown in the arterial vascular system, where some progestins may reduce the endothelium-dependent vasodilating action of estrogens and stimulate intima proliferation and upregulate thrombin receptor expression while other progestins did not.