Valproic acid has been widely used for the treatment of epilepsy. Although it is usually well tolerated, it has been associated with some side effects. A poor studied side effect is the hyperammonemia, which independs from the drug hepatotoxic action. The hyperammonemia may occurs just after the beginning or during the treatment and is characterized by vomiting, progressive impairment of consciousness, focal neurologic signs and increased seizure frequency. We report boy a 6 year-old boy who presented with hyperammonemia during the use of valproic acid within the therapeutic range. Complementary investigation was negative for aminoacidopathy, organic acidemia and urea cycle disorders. The hypothesis of secondary effect to the valproic acid was reinforced by the normalization of ammonia levels after drug withdrawal. The pathogenesis of valproate-induced hyperammonemia have been discussed. We conclude that routine monitoring of ammonia blood concentration are strongly recommended in patients under valproic acid treatment.
hyperammonemia; encephalopathy; valproic acid; epilepsy