Drug Interaction Report

MONITOR: Phenytoin and other hydantoins may induce the CYP450 3A4 hepatic metabolism of corticosteroids and increase their clearance and decrease their half-lives, possibly reducing their therapeutic efficacy. In addition, results of the dexamethasone adrenal suppression test may be unreliable in patients concurrently taking phenytoin. Hydrocortisone appears to be affected to a lesser extent than other corticosteroids. Some corticosteroids have also been reported to cause increases or decreases in serum phenytoin levels; however, data have been inconsistent.

MANAGEMENT: Patients should be closely monitored for clinical and laboratory evidence of reduced corticosteroid effects and changes in phenytoin concentrations during concomitant therapy. Some patients may require increased corticosteroid dosages.