Fosphenytoin

CEREBYX

Open Fosphenytoin in the interactive console ↗

What it isWater-soluble IV or IM prodrug of phenytoin; status epilepticus loading and short-term parenteral substitution.

Why this oneIt can be infused faster and causes less local tissue injury than IV phenytoin; IM administration is possible.

What limits itRapid IV infusion can cause severe hypotension and fatal arrhythmia—monitor ECG and blood pressure. Prescribe in phenytoin-equivalent units.

FDA-approved for

seizures (IV/IM) (1996)

FDA label

Read the full label on DailyMed ↗

BOXED WARNING Cardiovascular risk with rapid infusion: do not exceed 150 mg PE/min in adults and 2 mg PE/kg/min (or 150 mg PE/min) in pediatric patients; monitor cardiac/respiratory status.

FDA dosing	Population	Start	Target	Max
Status epilepticus	Adult	15-20 mg PE/kg IV loading at 100-150 mg PE/min	maintenance 4-6 mg PE/kg/day divided	per level
Status epilepticus	Pediatric	15-20 mg PE/kg IV loading at 2 mg PE/kg/min (or 150 mg PE/min, whichever slower)	per level	per level
Non-emergent loading and maintenance	Adult	10-20 mg PE/kg IV or IM loading	4-6 mg PE/kg/day divided	per level
Non-emergent loading and maintenance	Pediatric	10-15 mg PE/kg loading at 1-2 mg PE/kg/min (or 150 mg PE/min, whichever slower)	2-4 mg PE/kg q12h at 1-2 mg PE/kg/min	per level

Renal Monitor unbound phenytoin concentrations in renal disease or hypoalbuminemia

Hepatic Monitor unbound phenytoin concentrations in hepatic disease or hypoalbuminemia

Concentration is 50 mg PE/mL; a 10 mL vial contains 500 mg PE total.

Instructions

Always dose, concentrate, and infuse in phenytoin sodium equivalents (PE); no molecular-weight conversion needed
Do not confuse vial concentration (50 mg PE/mL) with total vial content
Should ordinarily not be given intramuscularly for status epilepticus
Discontinue gradually to avoid precipitating status epilepticus

Contraindications

Sinus bradycardia, sino-atrial block, second/third-degree AV block, or Adams-Stokes syndrome
History of prior acute hepatotoxicity attributable to fosphenytoin or phenytoin
Coadministration with delavirdine

Cautions

Dosing errors (PE vs concentration)
Withdrawal-precipitated seizure/status epilepticus
Serious dermatologic reactions (SJS/TEN)
DRESS/multiorgan hypersensitivity
Hypersensitivity (cross-sensitivity with hydantoins)
Angioedema
Hepatic injury
Hematopoietic complications
Cardiac effects with rapid infusion
Suicidal behavior/ideation

Adverse reactions

Nystagmus
Dizziness
Pruritus
Paresthesia
Headache
Somnolence
Ataxia

Pregnancy Prenatal phenytoin (active metabolite) exposure may increase risk of congenital malformations and adverse developmental outcomes.

Lactation Undefined

⚠ BOXED WARNING

Rapid IV infusion can cause severe hypotension and fatal cardiac arrhythmias; do not exceed the recommended rate and monitor cardiac rhythm and blood pressure during and after infusion

Cost, est. cash$20–$1,500/dose or month

Generic entry2007

Classes and tags

Clinical profile

Therapeutic safety burden3 / 4

Overdose danger4 / 4

Weight-gain liability1 / 4

Sedation liability1 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk2 / 4

Legacy pregnancy categoryD

Defining liabilityCardiovascular collapse with rapid administration and phenytoin-related nonlinear toxicity.

Active metabolites

Phenytoin

Mechanism of action: Fosphenytoin ballicule

Fosphenytoin ballicule: receptor binding, kinetics and half-life diagram

Open Fosphenytoin in the interactive console ↗

Memory aids: mascots and interaction avatars

Fosphenytoin CEREBYX mascot mnemonic cartoon — **“Cerebral Fox phenytoin”**
Variation of phenytoin mascot
Water-soluble phenytoin prodrug for IV/IM loading

Open Fosphenytoin in the interactive console ↗