Fosphenytoin

Provider Level

RN/Paramedic

Class

Anticonvulsant

Mechanism of Action

Water-soluble prodrug of phenytoin. Stabilizes neuronal membranes and limits the spread of seizure activity by modulating voltage-dependent sodium channels.

Indications

Status epilepticus, prevention and treatment of seizures during neurosurgery or following severe head trauma.

Contraindications

Hypersensitivity to fosphenytoin or phenytoin, sinus bradycardia, sinoatrial block, second and third-degree AV block, and Adams-Stokes syndrome.

Routes

IM, IV, IO

Onset / Duration

Onset: 15-30 minutes. Duration: 12-24 hours.

Adverse Effects

Hypotension, vasodilation, cardiovascular collapse, dizziness, somnolence, ataxia, nystagmus, pruritus, tinnitus.

Precautions & Interactions

Requires continuous ECG and blood pressure monitoring during IV administration due to risk of severe cardiovascular reactions including hypotension and arrhythmias.

Special Considerations

Always prescribed and dosed in phenytoin sodium equivalents (PE). Causes significantly less tissue irritation and necrosis than phenytoin if extravasation occurs.