Valproic acid, unlike other anticonvulsants, has no effect on methadone metabolism: two cases

Two patients who were concomitantly undergoing methadone maintenance treatment and receiving phenytoin suffered continuing opioid withdrawal symptoms as a results of phenytoin's acceleration of methadone metabolism. When anticonvulsant therapy was discontinued, these patients had seizures. One patient was switched to carbamazepine as an alternative anticonvulsant, but this treatment resulted in a similar clinical problem. When both patients received valproic acid instead, the withdrawal symptoms disappeared and their conditions stabilized.