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Valproate-induced hyperammonemic encephalopathy in the presence of topiramate

From the Department of Neurology, University of Marburg, Marburg, Germany.

Address correspondence and reprint requests to Dr. H.M. Hamer, Department of Neurology, University of Marburg, Rudolf-Bultmann-Str. 8, 35033 Marburg, Germany; e-mail: hamer{at}mailer.uni-marburg.de

Two adult patients with focal epilepsy who tolerated valproate (VPA) well in different combinations of anticonvulsants developed hyperammonemic encephalopathy when treated with VPA in combination with topiramate (TPM). Topiramate may contribute to the increased ammonia level by its inhibition of carbonic anhydrase and cerebral glutamine synthetase, thereby facilitating VPA/TPM hyperammonemic encephalopathy. Recovery occurred after withdrawal of VPA or TPM.

Key words: Valproate—Topiramate—Adverse effect—Ammonia—Encephalopathy

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