However, optimal seizure control is very important during pregnancy so drug may be continued if benefits outweigh the risks. Due to decreased drug concentrations as a result of plasma volume expansion during pregnancy, dose of phenytoin may need to be increased if only option for seizure control. Breastfeeding: The manufacturer does not recommend breastfeeding since 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. Intravenous use is contraindicated in patients with sinus bradycardia, sinoatrial block, second- or third-degree atrioventricular block, Stokes-Adams syndrome, or hypersensitivity to phenytoin, other hydantoins or any ingredient in the respective formulation. Side effects
Common side effects include nausea, stomach pain, loss of appetite, poor coordination, increased hair growth, and enlargement of the gums. Potentially serious side effects include sleepiness, self harm, liver problems, bone marrow suppression, low blood pressure, and toxic epidermal necrolysis. There is evidence that use during pregnancy results in abnormalities in the baby. Its use appears to be safe during breastfeeding. Alcohol may interfere with the medications effects. Heart and blood vessels
Severe low blood pressure and abnormal heart rhythms can be seen with rapid infusion of IV phenytoin. IV infusion should not exceed 50 mg/min in adults or 1–3 mg/kg/min (or 50 mg/min, whichever is slower) in children. Heart monitoring should occur during and after IV infusion. Due to these risks, oral phenytoin should be used if possible.
Focal seizures: Mainly used to protect against the development of focal seizures with complex symptomatology (psychomotor and temporal lobe seizures). Also effective in controlling focal 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: Intravenous formulation is drug of choice for arrhythmias caused by cardiac glycoside toxicity. Trigeminal neuralgia: Second choice drug to carbamazepine. Special considerations
Phenytoin has a narrow therapeutic index. Its therapeutic range for an anticonvulsant effect is 10–20 μg/mL and for an antiarrhythmic effect 10–20 μg/mL. The most common cause of phenytoin intoxication is self‑medication, which accounts for more than thirty percent of the cases. Avoid giving intramuscular formulation unless necessary due to skin cell death and local tissue destruction. Elderly patients may show earlier signs of toxicity. In the obese, ideal body weight should be used for dosing calculations. Pregnancy: Pregnancy category D due to risk of fetal hydantoin syndrome and fetal bleeding.