Mephenytoin Overdose—Phenytoin Poisoning Incognito? Case Report and Mephenytoin/Phenytoin Comparison

Abstract

Background: Unlike phenytoin, overdose from mephenytoin (CAS No. 50-12-4) is rare. A review of mephenytoin shows a number of differences from phenytoin, including structural, metabolic, pharmacodynamic, and toxicologic effects. Mephenytoin metabolism is also characterized by genetic polymorphism, which can result in prolonged elimination. Routine blood testing for phenytoin may show no interference from mephenytoin. Mephenytoin levels are not readily available nor clinically useful when they do become available; urine toxicology screen may be positive for barbiturates. Case Report: A 26-year-old female overdosed on approximately 12 g of mephenytoin and an unknown amount of valproic acid. She became comatose, developing pulmonary aspiration and pancreatitis with fever. Her Intensive Care Unit treatment was prolonged with slow resolution over 10 days. A review of mephenytoin and comparison to phenytoin overdose is provided in the context of this case report.