Drug Interaction Report

According to the manufacturer, methylphenidate may inhibit the metabolism of anticonvulsants including phenobarbital, phenytoin, and primidone. There have been only isolated case reports of phenytoin intoxication during coadministration with methylphenidate and none for the other anticonvulsants. Moreover, two studies found little or no effect of methylphenidate on plasma phenytoin concentrations. Thus, available evidence does not seem to support a clinically significant drug interaction. Nevertheless, it may be appropriate to monitor the pharmacologic response to these anticonvulsants more closely whenever methylphenidate (racemic) or dexmethylphenidate (the more pharmacologically active d-enantiomer) is added to or withdrawn from therapy, and the anticonvulsant dosage adjusted as necessary.

GENERALLY AVOID: Concurrent acute use of barbiturates and ethanol may result in additive CNS effects, including impaired coordination, sedation, and death. Tolerance of these agents may occur with chronic use. The mechanism is related to inhibition of microsomal enzymes acutely and induction of hepatic microsomal enzymes chronically.

MANAGEMENT: The combination of ethanol and barbiturates should be avoided.