Phenytoin (Dilantin)

Primer

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

Pharmacokinetics

See also article: Introduction to Pharmacology

Pharmacokinetics of Phenytoin

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

See also article: Cytochrome (CYP) P450 Metabolism

Phenytoin: Cytochrome P450 Metabolism

Substrate of (Metabolized by)
Induces
Inhibits

Pharmacodynamics

Mechanism of Action

Blocks Na+ channels

Toxicity

Indications

Seizure disorder

Dosing

See also: Abernethy, D. R., & Greenblatt, D. J. (1985). Phenytoin disposition in obesity: determination of loading dose. Archives of neurology, 42(5), 468-471.

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

See main article: Geriatric Pharmacology

Pediatric

See main article: Pediatric Pharmacology

Obstetric and Fetal

See main article: Obstetric and Fetal Pharmacology

Medically Ill

See main article: Psychotropic Dosing in the Medically Ill

Resources

The Complete (but Practical) Guide to Phenytoin Dosing

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