Chronic use of Phenytoin Induced Ataxia: A Case Series of Six Patients

Phenytoin-induced ataxia increased the risk of morbidity by 10% to 50% and could be life-threatening but rarely fatal. We reported six cases of phenytoin-induced ataxia, experienced with cerebellar signs of ataxia. All study patients were found with elevated phenytoin serum concentrations (range: 30-40 mcg/ml). Assessment of SARA (Scale for the Assessment and Rating of Ataxia) scale indicated mild ataxia among all patients. Naranjo’s algorithm shows 50% of patients had definite and another 50% had probable relation between phenytoin exposure and ataxia. Ataxia resulted in the withdrawal of phenytoin among five patients and dose reduction in one patient. All patients were treated with alternative antiseizure medications along with supportive treatment and they were symptomatically better within 1-6 weeks duration of treatment. Hence, this study concluded that phenytoin-induced ataxia is common at a plasma concentration of 30 to 40 mcg/ml. Prescribers and pharmacists need to focus on monitoring phenytoin serum levels and providing appropriate counseling to prevent their toxicity.