Phenytoin is a choice of drug for the treatment of epilepsy. It is categorized under drugs with narrow therapeutic range. Adverse effects of phenytoin observed in patients are gum hypertrophy, dystonia, myoclonus, abnormal muscle movement and rarely ballismusand ataxia. We report a case of a 32-year-old female, who had chief complaints of ataxia, oscillopsia, dizziness and nausea. She had past medical history of epilepsy and was taking phenytoin from the past 10 years. Treatment was started after tapering the dose of phenytoin, finally discontinuing, she was prescribed with valproic acid as an alternative for phenytoin. Present case report describes the phenytoin toxicity that helps to create awareness among physicians. There should be proper monitoring of plasma concentration of phenytoin to avoid its toxicity in the patients on chronic drug therapy so that drug dosage can be tailored as per the pharmacokinetic needs of the patient.
Key words: Ataxia, Phenytoin Toxicity, Oscillopsia, Therapeutic Drug Monitoring, Phenytoin.