zantac and Dilantin Interactions

Interactions between zantac(ranitidine) and Dilantin (phenytoin)

ranitidine and phenytoin (Moderate Drug-Drug)

GENERALLY AVOID: Cimetidine and ranitidine may significantly increase plasma phenytoin concentrations and toxicity has been reported. Increased phenytoin concentrations of up to 141% have been reported with cimetidine. The mechanism is related to inhibition of CYP450 enzymes responsible for hydantoin metabolism. This interaction may be expected with other hydantoins. This interaction has not been reported with famotidine or nizatidine.

MANAGEMENT: Concomitant use of cimetidine or ranitidine and phenytoin is not recommended. If no alternatives exist, clinical monitoring of patient response, tolerance, and serum phenytoin concentrations is recommended, especially during the first month of therapy. Patients should be advised to notify their physician if they experience symptoms of toxicity, including drowsiness, visual disturbances, change in mental status, seizures, nausea, or ataxia. The hydantoin dose may need to be decreased.