Evidence for immune etiology in clozapine-induced thrombocytopenia of 40 months' duration: a case report.

Platelet dysfunction and thrombocytopenia rarely occur during clozapine therapy, but constitute an important source of morbidity and mortality if they are not detected and therapy is discontinued. The manufacturer recommends discontinuing clozapine when the platelet count falls below 100,000/muL and resuming therapy when the count returns to within normal range (150,000-450,000/muL). If thrombocytopenia recurs, clozapine should be permanently discontinued. The authors report a rare case of long-term thrombocytopenia persisting 40 months postclozapine treatment. In addition, increased in vitro platelet [14C]serotonin release was observed in the presence of the drug, suggesting an immune-related cause for the thrombocytopenia.