Unmasking Anxiety: Unusual Presentation of Phenytoin Toxicity

Phenytoin, a widely used anticonvulsant, is known for it’s complex pharmacokinetics and a narrow therapeutic index, which can predispose patients to toxicity. While it’s primary mechanism of action involves blocking voltage-sensitive sodium channels, the drug’s effects extend beyond seizure control, impacting various neurological and psychiatric functions. We report a patient who was showing toxicity symptoms in the form of mood, behaviour, and cognitive symptoms, with certain cerebellar signs. The patient’s serum phenytoin was found to be quite high (>40.0 ng/ml). The symptoms were attributed to phenytoin toxicity, which responded within 2 weeks by reducing the dose of phenytoin (with a resultant fall in levels of serum phenytoin) and the addition of folic acid.