Abstract

PIP: As a result of the lowering of the estrogen and progestogen dosage of many oral contraceptives (OCs) and the avoidance of prescribing OCs to women at high risk, the relative risk of venous thromboembolic disease and myocardial infarction associated with OC use has been dramatically reduced. Many factors related to but not directly associated with the pharmacologic effect of OCs influence the safety of this method of contraception. Evaluation of the potential thrombogenic effect of OCs requires consideration of factors such as exercise, smoking, and medications, as well as the differential effect the various constituents of OCs have on the coagulation-fibrinolytic mechanism. Moreover, it is necessary to differentiate the effects on arterial and on venous thrombosis. A thrombus is likely to form when alterations in blood flow and an enchancement of the coagulation cascade are superimposed on an area of intimal damage, in the absence of normal anticoagulant and fibrinolytic activity. The estrogen component of OCs is believed to have a demanding effect on the fibrinolytic activity on vein walls; however, exercise can increase fibrinolytic activity in healthy women. Data on the effect of OCs on platelet function are contradictory due to technical difficulties of the tests of such function. Platelet aggregation is increased after longterm OC use and in individuals taking estrogen alone, but remains normal when only progesterone is used. Most of the individual clotting factors, especially fibronogen, prothrombin, and factors VII, IX, X, and XII, are elevated in OC users; this effect appears to be related to estrogen and has no bearing on the actual risk of inappropriate thrombus formation. Assessment of the thromboembolic potential of various OCs must take into account factors that will increase (smoking) or decrease (exercise) the risk of OC-induced thrombosis. Individual assessment and close monitoring of measurable adverse signs should allow most healthy women under age 35 years to use OCs safely.