Phenytoin (Dilantin)

Primer

Phenytoin (Trade name: Dilantin) is an antiepileptic used in the treatment of seizure disorder.

Pharmacokinetics

Pharmacokinetics of Phenytoin

Absorption
Distribution
Metabolism
Elimination Zero-order kinetics elimination
Half-life

Phenytoin: Cytochrome P450 Metabolism

Substrate of (Metabolized by)
Induces
Inhibits

Pharmacodynamics

Mechanism of Action

  • Blocks Na+ channels

Toxicity

Indications

  • Seizure disorder

Dosing

  • Usual maintenance dose is 4-6 mg/kg and adjusted body weight
  • Once increased to the correct dose, and the level should be measured in 3 and 7 days

Formulations

  • Phenytoin comes in oral and liquid forms.

Monitoring

  • Albumin level should be monitored as well

Contraindications

Absolute

Relative

Drug-Drug Interactions

Side Effects

Mnemonic

The mnemonic PHENYTOIN can be used to remember the side effects and adverse events related to its use:
  • P - cytochrome P-450 induction
  • H - Hirsutism
  • E - Enlarged gums
  • N - Nystagmus
  • Y - Yellow-brown skin
  • T - Teratogen (fetal hydantoin syndrome)
  • O - Osteopenia
  • I - Inhibited folate absorption
  • N - Neuropathy

Adverse Events

  • Rarely can cause Stevens-Johnson Syndrome, Drug rash with eosinophilia and systemic symptoms (DRESS) syndrome, lupus-like syndrome
  • Toxicity leads to diplopia, ataxia, and sedation

Clinical Pearls

Special Populations

Geriatric

Pediatric

Obstetric and Fetal

Medically Ill

Resources