Valproic acid (VPA) is an antiepileptic drug which is used in the treatment of various seizure disorders including tonic-clonic, myoclonic, absence, partial seizures and psychiatric disorders. VPA is usually well tolerated, but severe adverse effects may occur. Hyperammonaemic encephalopathy (HE) is a rare and potentially fatal complication of VPA treatment. The mechanism by which valproate induces hyperammonemia remains incompletely understood but is likely to relate to the urea cycle. Herein we present two cases with valproate-induced hyperammonemia at therapeutic valproate levels without signs of liver failure and were successfully treated by a single dose of carglumic acid.

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