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Phenytoin Hepatotoxicity: A Review of the Literature

Phenytoin hepatotoxicity is a serious idiosyncratic reaction that occurs in less than one percent of patients. The onset of symptoms occurs early in therapy, usually within the first six weeks. Presenting symptoms often include fever, rash, lymphadenopathy, hepatomegaly, anorexia, and myalgias or arthralgias. Other significant findings that may develop throughout hospitalization are jaundice, periorbital or facial edema, and splenomegaly. The following alterations in liver function tests are associated with phenytoin hepatotoxicity: elevations in serum aminotransferases, lactic dehydrogenase, alkaline phosphatase, bilirubin, and prothrombin time. Rechallenges, lymphocyte stimulation test, and liver biopsy have been used to aid in the diagnosis. Rechallenge is the most definitive diagnostic approach; however, its use is limited by the potential of a fatal reaction. Although the exact mechanism of phenytoin hepatotoxicity is unknown, the majority of literature supports a hypersensitivity mechanism. The severity of this adverse effect ranges from self-limiting to fatal. Since 1965 six fatal cases have been reported. To date, sufficient evidence is not available to establish treatment guidelines. Discontinuation of phenytoin therapy is warranted.