Severe thrombocytopenia associated with phenytoin and cimetidine therapy.

A 67-year-old man developed a sudden onset of severe isolated thrombocytopenia (platelet count, 1000/mm3) after 10 days of phenytoin administration as a prophylactic measure prior to craniotomy. The patient had also been taking cimetidine for 2 months prior to admission. No other hematological complications were noted, and an extensive hematologic investigation was otherwise unremarkable. Rapid resolution of the thrombocytopenia upon discontinuation of phenytoin and cimetidine strongly suggests a drug-induced adverse reaction.