Special considerations Phenytoin has a narrow therapeutic index. Its therapeutic range for both anticonvulsant and antiarrhythmic effect is 10–20 μg/mL. 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. 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.Phenytoin [package insert]. New York, NY: Pfizer Inc.; 2013. Accessed 2 November 2014. 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.
Special considerations Phenytoin has a narrow therapeutic index. Its therapeutic range for both anticonvulsant and antiarrhythmic effect is 10–20 μg/mL. 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. 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.Phenytoin [package insert]. New York, NY: Pfizer Inc.; 2013 Accessed 2 November 2014. 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.