[Immunomechanisms in drug-induced hemolytic anemias]

Among the acquired hemolytic anemias, drug-induced immune hemolytic anemias (IHA) play a significant role. Many different drugs are capable of causing IHA, alphamethyldopa and penicillins have been responsible for the greatest number of cases. For the majority of the other drugs single cases of IHA are reported. Drug-induced immune hemolysis may be mediated by different immune mechanisms including the immune cytotoxicity type (penicillins and cephalosporins) with predominantly extravascular hemolysis. Immune hemolysis of most other drugs is due to immune complexes formed by the drug and specific antibodies leading to intravascular hemolysis in the presence of complement activation. So far, the autoimmune type of IHA caused by alphamethyldopa is unexplained, serologically this form cannot be distinguished from warm antibody auto-IHA. The clinical importance of drug-induced IHA depends on the severity of anemia and the problem of diagnosis leading to adequate therapeutic measures. Only a small number of cases showing a positive direct antiglobulin (Coombs') test caused by drugs will develop IHA. Therefore this finding does not require absolutely withdrawal of the drug, but careful observation of the patient. The diagnosis of drug-induced IHA is necessary for its distinction from auto-IHA and other secondary IHA. The study of such IHA has great importance for the understanding of other drug-induced cytopenias and may give explanations of the pathogenetic mechanisms of yet unexplained autoimmune phenomena.