Both acetylsalicylic acid (aspirin, ASA) and dipyridamole have been used in HIT patients with variable success (Janson et al., 1983; Makhoul et al., 1986; Kappa et al., 1987, 1989; Laster et al., 1989; Gruel et al., 1991; Hall et al., 1992; Almeida et al., 1998). Sometimes the platelet count appeared to rise promptly with the application of antiplatelet therapy (Warkentin, 1997). However, HIT antibodies are potent platelet activators, and their effect cannot always be blocked in vitro by ASA or dipyridamole—indeed, HIT has occurred in patients who receive dual antiplate-let therapy with ASA and clopidogrel) (Selleng et al., 2005). These antiplatelet agents may be used as adjunctive therapy (to anticoagulant therapy), particularly in patients with arteriopathy. A potential drawback is increased bleeding (especially when combined with other antithrombotic agents).
Recommendation. Antiplatelet agents, such as aspirin or clopidogrel, may be used as adjuncts to anticoagulant therapy of HIT, particularly in selected (arteriopathic) patients at high risk for arterial thromboembolism. The possible benefit in preventing arterial thrombosis should be weighed against the potential for increased bleeding (grade 2C).
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