Seizures Tonic-clonic seizures: Mainly used in the prophylactic management of tonic-clonic seizures with complex symptomatology (psychomotor seizures). A period of 5–10 days may be required to achieve anticonvulsant effects. Focal seizures: Mainly used to protect against the development of focal seizures with complex symptomatology (psychomotor and temporal lobe seizures). Also effective in controlling partial seizures with autonomic symptoms. Absence seizures: Not used in treatment of pure absence seizures due to risk for increasing frequency of seizures. However, can be used in combination with other anticonvulsants during combined absence and tonic-clonic seizures. Seizures during surgery: A 2018 meta-analysis found that early antiepileptic treatment with either phenytoin or phenobarbital reduced the risk of seizure in the first week after neurosurgery for brain tumors. Status epilepticus: Considered after failed treatment using a benzodiazepine due to slow onset of action. Other Abnormal heart rhythms: may be used in the treatment of ventricular tachycardia and sudden episodes of atrial tachycardia after other antiarrhythmic medications or cardioversion has failed. It is a class 1b antiarrhythmic. Digoxin toxicity: IV formulation is drug of choice for arrhythmias caused by cardiac glycoside toxicity. Trigeminal neuralgia: Second choice drug to carbamazepine. Special considerations Monitoring plasma concentrations: Narrow therapeutic index. Anticonvulsant effect: 10–20 µg/mL; Antiarrhythmic effect: 10–20 µg/mL Avoid giving intramuscular formulation unless necessary due to skin cell death and local tissue destruction. Elderly: May show earlier signs of toxicity. Obese: Use ideal body weight for dosing calculations. Pregnancy: Pregnancy Category D due to risk of fetal hydantoin syndrome and fetal bleeding. However, optimal seizure control is very important during pregnancy so drug may be continued if benefits outweigh the risks. Due to decreased drug concentrations during pregnancy, dose of phenytoin may need to be increased if only option for seizure control. Breast feeding: The manufacturer does not recommend breast feeding because low concentrations of phenytoin are excreted in breast milk. Liver disease: Do not use oral loading dose. Consider using decreased maintenance dose. Kidney disease: Do not use oral loading dose. Can begin with standard maintenance dose and adjust as needed. IV use is contraindicated in patients with sinus bradycardia, SA block, second- or third-degree AV block, Stokes-Adams syndrome, or hypersensitivity to phenytoin, other hydantoins or any ingredient in the respective formulation.