Drug-induced immune thrombocytopenia.

Copyright © 2007 Massachusetts Medical Society. Drug-induced thrombocytopenia can be caused by dozens, perhaps hundreds, of medications. Because thrombocytopenia can have many other causes, the diagnosis of drug-induced thrombocytopenia can easily be overlooked. On occasion, outpatients with drug-induced thrombocytopenia are treated for autoimmune thrombocytopenia and can have two or three recurrences before the drug causing the disorder is identified.1 In acutely ill, hospitalized patients, drug-induced thrombocytopenia can be overlooked because thrombocytopenia is attributed to sepsis, the effect of coronary-artery bypass surgery, or some other underlying condition. Although drug-induced thrombocytopenia is uncommon, it can have devastating, even fatal consequences that can usually be prevented simply by discontinuing the causative drug. It is therefore important that clinicians have a general understanding of this condition and the drugs that can cause it. In this review, we focus on conditions in which exposure to a drug leads to the destruction of circulating platelets, often accompanied by bleeding symptoms. We do not consider thrombocytopenia resulting from dose-dependent hematosuppression, which often occurs after treatment with chemotherapeutic and immunosuppressive agents such as cisplatin and cyclophosphamide.2 Although heparin-induced thrombocytopenia is the most common drug-related cause of a drop in the platelet count, we do not discuss this condition because of its complexity and because thrombosis, rather than thrombocytopenia, is the major threat to an affected patient. Because heparin is often given together with certain drugs that are likely to cause drug-induced thrombocytopenia (platelet inhibitors and vancomycin), it is important to distinguish between heparin-induced thrombocytopenia and druginduced thrombocytopenia. Heparin-induced thrombocytopenia was recently reviewed in the Journal.3 Drug-induced platelet destruction is usually caused by drug-induced antibodies, but this can be difficult to prove. In this review, we include many conditions for which an immune cause has not yet been fully documented. Although platelets are the preferred targets of drug-induced antibodies, drugs can also cause immune hemolytic anemia4 and neutropenia5 through similar mechanisms.