ACUTE PHENYTOIN TOXICITY FOLLOWED BY SEIZURE BREAKTHROUGH FROM A TICLOPIDINE-PHENYTOIN INTERACTION

Objective: To review a case of a drug-drug interaction between phenyto in sodium and ticlopidine hydrochloride that resulted in acute phenyto in toxicity and permanent memory loss. Case Report: A 63-year-old man who was maintained with a stable dose of phenytoin for treatment of se izures began treatment with ticlopidine following percutaneous translu minal angioplasty and stent placement. Within 3 weeks of beginning tre atment with ticlopidine, he experienced acute clinical toxic effects o f phenytoin with a maximum measured phenytoin concentration of 162.4 m u mol/L. Phenytoin concentration decreased to 36 mu mol/L after discon tinuing treatment with ticlopidine and reducing the phenytoin dose. Su bsequently, the patient developed probable complex partial status epil epticus. Conclusions: Ticlopidine is a metabolic inhibitor of several drugs. Because of the potential for acute and permanent adverse effect s from a drug-drug interaction, phenytoin concentrations should be car efully monitored when beginning or ending ticlopidine therapy.