Possible atypical cross-sensitivity between phenytoin and carbamazepine inthe anticonvulsant hypersensitivity syndrome

Anticonvulsant hypersensitivity syndrome (AHS) is a rare but potentially li fe-threatening reaction that occurs in response to common anticonvulsants i n predisposed individuals. It is often characterized by fever, rash, lympha denopathy, hepatitis, and laboratory abnormalities. Consequently, it often is overlooked or even misdiagnosed by practitioners unfamiliar with AHS. Cr oss-sensitivity manifests frequently between phenytoin, phenobarbital, and carbamazepine as an exacerbation of presenting signs and symptoms. We repor t a case of AHS in a patient whose clinical features changed significantly when switching from phenytoin to carbamazepine. Physicians and pharmacists must become aware of the extreme variability in AHS manifestation so that t he offending anticonvulsant regimen can be discontinued in a timely manner.