Clinical aspects of heparin-induced thrombocytopenia and thrombosis and other side effects of heparin therapy.

Heparin, first used to prevent the clotting of blood in vitro, has been clinically used to treat thrombosis for more than 50 years. Although several new anticoagulant drugs are in development, heparin remains the anticoagulant of choice to treat acute thrombotic episodes. The clinical effects of heparin are meritorious, but side effects do exist. Bleeding is the primary untoward effect of heparin. Major bleeding is of primary concern in patients receiving heparin therapy. However, additional important untoward effects of heparin therapy include heparin-induced thrombocytopenia, heparin-associated osteoporosis, eosinophilia, skin reactions, allergic reactions other than thrombocytopenia, alopecia, transaminasemia, hyperkalemia, hypoaldosteronism, and priapism. These side effects are relatively rare in a given individual, but given the extremely widespread use of heparin, some are quite common, particularly HITT and osteoporosis. Although reasonable incidences of many of these side effects can be "softly" deduced from current reports dealing with unfractionated heparin, at present the incidences of these side effects with newer low molecular weight heparins appear to be much less common. However, only longer experience will more clearly define the incidence of each side effect with low molecular weight preparations.