A wide range of medications can cause life-threatening
immune thrombocytopenia (
ITP),
hemolytic anemia, or
neutropenia in sensitive individuals. The
antibodies associated with these conditions usually require soluble drug to be present in order to react with the cell membrane
glycoproteins for which they are specific. However, some patients make drug-independent
antibodies (
autoantibodies) as well. Occasionally, only
autoantibodies are produced following exposure to a drug. Although drugs and other small molecules can become conjugated to
proteins in vivo, which may induce an immune response, only fragmentary information is available to explain how exogenous substances sometimes perturb the immune system in such a way that
antibodies capable of causing immune
cytopenia are produced. Platelets are affected by drug-induced
antibodies more often than any other blood
element. For many drug-induced
thrombocytopenias, the targeted
membrane glycoproteins are readily accessible for laboratory investigation and methods for detecting the responsible
antibodies are well developed. Techniques for studying cellular aspects of the immune response induced by drugs through in vitro manipulation of T and B lymphocytes are also advancing rapidly. Studies of drug-induced
ITP may provide clues to the general mechanisms whereby drugs and other
xenobiotics induce
immune diseases. Clinicians should consider the possibility of an exogenous trigger in patients who present with apparent
autoimmune thrombocytopenia.