Primidone-induced hyperammonemic encephalopathy in a patient with cerebral astrocytoma.

A case of a patient with astrocytoma who showed somnolence and asterixis one month after tumour resection is presented. Although primidone had been prescribed preoperatively for five years and the same dose was maintained after the operation, the serum concentration of the primidone metabolite phenobarbital was elevated and she demonstrated hyperammonemic encephalopathy, which disappeared on withdrawal of the drug. A description of this seldom reported phenomenon during primidone therapy is given, with reference to valproate cases. Copyright 2002 Harcourt Publishers Ltd.