[Oral contraceptive agents and antithrombin III]

Antithrombin III is one of the most important inhibitors of serine proteases of coagulation and fibrinolysis. It inhibits the activity of thrombin and factor X. Its congenital or acquired reduction leads to an increased risk of thrombosis. In their study the authors aimed to investigate the influence of oral contraceptive preparations--Gravistat and Nonovolan on the activity of antithrombin III. Thirty five women, receiving these drugs for a period of one month to ten years (on the average two and a half years were examined. All women received the drugs in accordance with the physician prescription, taking into consideration the lack of history data on increased frequency of thrombosis. Part of the examined group (the first ten on the table of the results) were smokers with mean usage of 15 cigarettes per day. The study was carried out on 25 women at the three stages of the hormonal cycle, but singly on the remaining 10 women in its beginning. Blood sample for examination was taken with anticoagulant (citrate) in the morning before breakfast and the activity of the inhibitor was determined by kinetic colorimetric method and chromatogenic Chromasin TN (a modification of Kamenov). The results were presented in percentages. The mean activity of antithrombin III was: means = 107.5%, which did not differ from the reference values. The activities at the three phases of the menstrual cycle did not differ significantly (p greater than 0.05). The results, obtained from the study, proved that hormonal contraceptive drugs did not reduce the activity of antithrombin III.