Dopaminergic effects of carbamazepine. Relationship to clinical response in affective illness

Carbamazepine, a drug used widely to treat epilepsy and trigeminal neuralgia, has been shown to be effective in the acute and prophylactic treatment of manic-depressive illness. While the time course of its antimanic effects parallels that of classic neuroleptics, indirect clinical evidence, such as lack of parkinsonian side effects and tardive dyskinesia, suggests that carbamazepine does not act by blocking dopamine receptors. To assess the effects of carbamazepine on dopamine mechanisms, we measured the dopamine metabolite homovanillic acid (HVA) in the cerebrospinal fluid of affectively ill patients before and after treatment. Carbamazepine did not alter basal concentrations of HVA, but decreased probenecid-induced accumulations of HVA, paralleling results in animal studies. In 25 patients, lower baseline cerebrospinal fluid HVA levels were related to subsequent better acute antidepressive responses to carbamazepine. While the precise mechanism of carbamazepine's effects on dopaminergic systems remains to be determined, this study provides further evidence that carbamazepine does not have a biochemical profile typical of neuroleptics.