Phenytoin Sodium (phenytoin sodium)

Phenytoin formulations containing the free acid form of the drug (oral suspension and chewable tablets) have approximately 8% greater drug content than phenytoin sodium formulations (extended-release capsules and injection); this difference should be considered if a patient is switched from the free acid form to the sodium salt form or vice versa.

Determination of serum phenytoin concentrations may be necessary to achieve optimal dosage adjustments. (See Therapeutic Drug Monitoring under Dosage and Administration: Administration.) Concurrent administration of many drugs can increase or decrease serum concentrations of phenytoin. (See Drug Interactions.)

Phenytoin and phenytoin sodium usually are administered orally in the management of seizure disorders. Phenytoin sodium also may be administered parenterally as a short-term replacement for oral phenytoin when oral administration is not possible. Phenytoin sodium is administered by slow IV injection or IV infusion in the treatment of status epilepticus. IM administration of phenytoin generally is not recommended because of the risk of necrosis, abscess formation, and erratic absorption. (See IM Administration under Dosage and Administration: Administration.) Because parenteral administration of phenytoin is associated with more frequent and severe complications, the oral route is preferred for maintaining therapeutic drug concentrations during nonemergency situations; patients receiving the drug parenterally should routinely be assessed for feasibility of oral therapy.

Phenytoin therapy should not be abruptly discontinued to avoid precipitating seizures or status epilepticus. (See Cautions: Precautions and Contraindications.) Dosage reduction, discontinuance of therapy, or substitution with another anticonvulsant should be done cautiously and slowly. When a patient is transferred from phenytoin to another anticonvulsant, dosage of phenytoin should be gradually reduced over a period of about 1 week while at the same time therapy is instituted with a low dosage of the replacement drug.

Patients who are currently receiving or beginning therapy with phenytoin, phenytoin sodium, and/or any other anticonvulsant should be closely monitored for notable changes in behavior that could indicate the emergence or worsening of suicidal thoughts or behavior or depression. (See Cautions: Precautions and Contraindications.)

No dosing information is available for this tab.

No dosing information is available for this tab.

Phenytoin is involved in multiple drug interactions because of its extensive plasma protein binding, saturable metabolism, and potent hepatic enzyme-inducing properties.

There are no contraindication interactions for this drug.

There are no severe interactions for this drug.

There are no moderate interactions for this drug.

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

There are no severe contraindications for this drug.

There are no moderate contraindications for this drug.

There is no enhanced messaging for this drug.

There are no severe adverse reactions for this drug.

There are no less severe adverse reactions for this drug.

No enhanced messaging available.

No enhanced messaging available.

Phenytoin may cause fetal harm (e.g., congenital malformations, adverse developmental outcomes) if used during pregnancy. However, the risk-to-benefit ratio generally favors continued use in pregnant women whose seizure control depends on the drug. (See Cautions: Pregnancy and Lactation, in the Anticonvulsants General Statement 28:12.) Phenytoin has been associated with a fetal hydantoin syndrome consisting of craniofacial abnormalities, nail and digital hypoplasia, prenatal growth deficiency, microcephaly, and cognitive deficiency; such effects have been observed in children born to epileptic women who received phenytoin alone or in combination with other anticonvulsant drugs during pregnancy. In addition to reports of a fetal hydantoin syndrome, there have been rare reports of malignancies, including neuroblastoma, in children whose mothers received phenytoin during pregnancy. Fetal malformations (e.g., craniofacial, cardiovascular, neural, limb, and digit abnormalities) and other evidence of developmental toxicity (e.g., embryofetal death, growth impairment, behavioral abnormalities) have been observed in animal reproductive studies.

Coagulation defects which have resulted in life-threatening bleeding disorders have been reported in neonates born to women receiving phenytoin during pregnancy; because these reactions are related to decreased concentrations of vitamin K-dependent clotting factors, administration of vitamin K to the mother prior to delivery and to the neonate after birth may prevent these complications.

Women who are pregnant while receiving phenytoin should be encouraged to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry by calling 888-233-2334; registry information also is available at https://www.aedpregnancyregistry.org.

Because of altered pharmacokinetics of phenytoin during pregnancy, serum concentrations of phenytoin may decline, possibly increasing the frequency of seizures in pregnant women receiving the drug. If phenytoin is administered during pregnancy, serum phenytoin concentrations should be monitored and dosage of phenytoin should be adjusted accordingly; however, restoration of the patient's usual dosage will probably be necessary postpartum. Because of potential changes in protein binding of phenytoin during pregnancy, it is recommended that unbound (free) phenytoin concentrations be monitored in pregnant women.

Phenytoin is distributed into milk; however, use of phenytoin is generally considered compatible with breast-feeding. The known benefits of breast-feeding should be considered along with the woman's clinical need for phenytoin and any potential adverse effects on the breast-fed infant from the drug or underlying maternal condition.

No enhanced messaging available.