section name header

Pronunciation

FEN-i-toyn

Classifications

Therapeutic Classification: antiarrhythmics (group IB), anticonvulsants

Pharmacologic Classification: hydantoins

Indications

REMS


Unlabeled Use:
  • As an antiarrhythmic, particularly for ventricular arrhythmias associated with digoxin toxicity, prolonged QT interval, and surgical repair of congenital heart diseases in children.
  • Management of neuropathic pain, including trigeminal neuralgia.

Action

  • Limits seizure propagation by altering ion transport.
  • May also decrease synaptic transmission.
  • Antiarrhythmic properties as a result of shortening the action potential and decreasing automaticity.
Therapeutic effects:
  • Diminished seizure activity.
  • Termination of ventricular arrhythmias.

Pharmacokinetics

Absorption: Absorbed slowly from the GI tract. Bioavailability differs among products; the Dilantin and Phenytek preparations are considered to be "extended" products. Other products are considered to be prompt release.

Distribution: Distributes into CSF and other body tissues and fluids. Enters breast milk; crosses the placenta, achieving similar maternal/fetal levels. Preferentially distributes into fatty tissue.

Protein Binding: Adults 90–95%; protein binding in neonates (up to 20% free fraction available), infants (up to 15% free), and patients with hyperbilirubinemia, hypoalbuminemia, severe renal dysfunction or uremia.

Metabolism/Excretion: Mostly metabolized by the liver via the CYP2C9 isoenzyme, and to a lesser extent by the CYP2C19 isoenzyme; the CYP2C9 isoenzyme exhibits genetic polymorphism (intermediate or poor metabolizers may have significantly phenytoin concentrations and an risk of adverse reactions); minimal amounts excreted in the urine.

Half-Life: 22 hr (range 7–42 hr).

Time/Action Profile

(anticonvulsant effect)

ROUTEONSETPEAKDURATION
PO2–24 hr (1 wk)*1.5–3 hr6–12 hr
PO-ER2–24 hr (1 wk)4–12 hr12–36 hr
IV0.5–1 hr (1 wk)rapid12–24 hr



*() = time required for onset of action without a loading dose.

Contraind./Precautions

Contraindicated in:

Use Cautiously in:

Adv. Reactions/Side Effects

Interactions

Drug-drug:

Drug-Natural Products:

Route/Dosage

Anticonvulsant

Antiarrhythmic

Availability

(Generic available)

Assessment

Lab Test Considerations:

Toxicity and Overdose:

Implementation

IV Administration:

Patient/Family Teaching

Evaluation/Desired Outcomes

US Brand Names

Dilantin, Phenytek

Canadian Brand Names

Tremytoine

Code

NDC Code