Phenytoin-induced cerebellar symptoms – A case report

Phenytoin, a hydantoin derivative, is an effective anticonvulsant drug widely used to treat seizure disorder. The wide pharmacokinetic variability and low toxicity threshold of phenytoin often contribute to its toxicity. We now report the case of a 43-year-old woman who was hospitalized with ataxia, nystagmus, external ophthalmoplegia, drowsiness, gingival hypertrophy, vomiting, and generalized weakness for 10 days while she was on treatment with T. phenytoin 200 mg/day for the past 6 months for seizure disorder. Two days before the onset of these symptoms, the dose of T. phenytoin was increased from 200 mg/day to 300 mg/day. Based on her signs, symptoms, and laboratory tests, she was diagnosed with phenytoin-induced poisoning. After stopping the medication, the symptoms improved. She started using oral levetiracetam instead. Based on the Naranjo and the World Health Organization, a causal analysis of the relationship between the patient’s symptoms and phenytoin use was done. The severity of this adverse drug reaction is moderate at level 4 on the Hartwig severity rating scale. These data highlight the adverse effects of phenytoin and the importance of clinical monitoring for a drug with a narrow therapeutic index.