Adverse neuropsychiatric effects of anticonvulsant drugs.

Clinical and electrical evidence of peripheral neuropathy may result from long term treatment with phenytoin or barbiturates, especially in combination, or after repeated exposure to toxic blood concentrations of either drug. Prolonged acute toxicity with phenytoin may rarely lead to permanent residual ataxia. Reversible dystonia may occasionally be precipitated by phenytoin or carbamazepine; asterixis by phenytoin, barbiturates or carbamazepine; and, more commonly, tremor by valproate. All the major anticonvulsant drugs, especially in combination, can produce occasional subacute cognitive or behavioural syndromes. In varying degrees, the drugs also impair attention, concentration, memory, mental speed or processing, or motor speed. Possible mechanisms of impaired mental function include neuronal damage, or disturbance of folic acid, monoamine or hormonal metabolism. The relative influence on neurological or psychological function is an important factor in the choice of anticonvulsant drug for the treatment of epilepsy.