Hyperammonemic topiramate

In two other cases the addition of topiramate was thought to have precipitated valproate-induced hyperammonemic encephalopathy (1172). Recovery occurred after withdrawal of valproate or topiramate. The authors suggested that topiramate may have contributed to the hyperammonemia by inhibiting carbonic anhydrase and cerebral glutamine synthetase. 

Valproate-induced hyperammonemic encephalopathy in the presence of topiramate. Neurology 2000 54(l) 230-2. 

In one patient there was a possible synergistic interaction of valproic acid and topir-amate with respect to the emergence of hyperammonemic encephalopathy [316 ]. The authors speculated that inhibition of carbonic anhydrase by topiramate might be the basis of this, since HCO is used in the sjmthesis of carbamoylphosphate in the urea cycle. 

Deutsch SI, Burket JA, Rosse RB. Valproate-induced hyperammonemic encephalopathy and normal liver functions possible synergism with topiramate. Clin Neuropharmacol 2009 32(6) 350-2. 

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