What should be monitored closely in a patient receiving phenytoin therapy?

Monitoring therapeutic drug levels in a patient receiving phenytoin therapy is crucial due to the drug's narrow therapeutic index. Phenytoin levels in the blood must be maintained within a specific range to avoid toxicity while ensuring effectiveness in controlling seizures. Since the pharmacokinetics of phenytoin can vary significantly between individuals, including factors such as metabolism and interactions with other medications, regular monitoring helps adjust dosages appropriately and prevent adverse effects.

Patients on phenytoin can exhibit toxic symptoms if levels exceed the therapeutic range, which can include neurological effects such as nystagmus, ataxia, and potentially more severe complications like Steven-Johnson syndrome. Therefore, clinicians must routinely check phenytoin levels to tailor treatment effectively and ensure patient safety.