The major complication of antithrombotic therapy is bleeding. For each antithrombotic drug, the antithrombotic efficacy must be balanced against the potential increased bleeding risk.
Clinical trials distinguish:
The criteria for defining the severity of bleeding vary considerably between studies, accounting in part for the variation in the rates of bleeding reported.
Heparin-induced thrombocytopenia
Heparin-induced thrombocytopenia (HIT) is a severe immuno-allergic adverse effect of heparin therapy mediated by antibodies, mostly antibodies against PF4 (platelet factor 4)/heparin complexes. HIT is most common in patients receiving UFH (0.5 to 5%), but also occurs in patients receiving LMWH (Jang and Hursting. Circulation 2005;111:2672-83).
Thrombosis rather than haemorrhage is the predominant clinical sign. If untreated: