section name header

Pronunciation

FEN-i-toyn

Classifications

Therapeutic Classification: antiarrhythmics (group IB), anticonvulsants

Pharmacologic Classification: hydantoins

Indications

REMS

Unlabeled Uses:

Action

Therapeutic Effects:

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:

Exercise Extreme Caution in:

Adv. Reactions/Side Effects

CV: hypotension ( with IV phenytoin), bradycardia, CARDIAC ARREST, tachycardia.

Derm: hypertrichosis, rash, ACUTE GENERALIZED EXANTHEMATOUS PUSTULOSIS, DRUG REACTION WITH EOSINOPHILIA AND SYSTEMIC SYMPTOMS (DRESS), exfoliative dermatitis, pruritus, purple glove syndrome, STEVENS-JOHNSON SYNDROME (SJS), TOXIC EPIDERMAL NECROLYSIS (TEN).

EENT: diplopia, nystagmus.

GI: gingival hyperplasia, nausea, constipation, drug-induced hepatitis, HEPATIC FAILURE, vomiting.

Hemat: AGRANULOCYTOSIS, APLASTIC ANEMIA, leukopenia, lymphadenopathy, megaloblastic anemia, pure red cell aplasia, thrombocytopenia.

MS: osteomalacia, osteoporosis.

Neuro: ataxia, agitation, confusion, dizziness, drowsiness, dysarthria, dyskinesia, extrapyramidal syndrome, headache, insomnia, SUICIDAL THOUGHTS, vertigo, weakness.
Misc: ANGIOEDEMA, fever.

Interactions

Drug-Drug:

Drug-Natural Products:

Drug-Food:

Route/Dosage

see Calculator

IM administration is not recommended due to erratic absorption and pain on injection. Oral route should be used whenever possible.

Anticonvulsant

Antiarrhythmic

Availability

(Generic available)

Assessment

Lab Test Considerations: Toxicity and Overdose:

Implementation

Patient/Family Teaching

Evaluation/Desired Outcomes

US Brand Names

Dilantin, Phenytek

Canadian Brand Names

Tremytoine