Journal of pharmacy practice
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Thrombocytopenia, defined as a platelet count less than 150 000/µL, occurs as a result of decreased production, sequestration, or peripheral destruction. Drug-induced thrombocytopenia is a clinically important adverse drug event involving many drugs including hydantoins. This report details an acute reaction of thrombocytopenia in a 55-year-old, critically ill, African American male patient after receiving a loading dose of fosphenytoin and a subsequent dose of IV phenytoin. ⋯ Most documented cases of thrombocytopenia occur after a week or longer of phenytoin administration with the coadministration of glucocorticoids and cimetidine or proton pump inhibitors. An immediate decrease in platelets as seen in this case has not been previously described in the literature. Such a rapid induction of thrombocytopenia from phenytoin is suggestive of a direct cytotoxic effect on circulating platelets.