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Fosphenytoin
From WikEM
Contents
General
- Type: Anticonvulsants
- Dosage Forms: IM/IV
- Common Trade Names: Cerebyx
Adult Dosing
- Generalized Convulsive Status Epilepticus
- 15-20mg/kg IV, infuse at 100-150mg/min
- Nonemergent Seizure
- Load: 10-20mg/kg IV/IM
- Initial Maintenance: 4-6mg/kg/day IV/IM
- Short-Term Substitution for PO Phenytoin
- Can be substituted for PO phenytoin therapy at the same total daily dose
- Administration
- Maximum IV rate of 150mg PE/min
- Monitor: phenytoin level 2 hr after IV, 4 hr after IM
- All dosing in mg "phenytoin equivalents" (PE); 75mg fosphenytoin equivalent to 50mg phenytoin
Pediatric Dosing
- Safety and efficacy not established
Special Populations
- Pregnancy Rating: D
- Lactation: excretion in milk unknown, not recommended
- Renal Dosing: not defined, caution advised
- Hepatic Dosing: not defined, caution advised
Contraindications
- Allergy to class/drug
- Sinus bradycardia, sinoatrial block, 2nd or 3rd degree AV block, Adams-Stokes syndrome
- Not indicated for absence seizures or seizures secondary to hypoglycemia or other metabolic disorder
- Coadministration with delavirdine; potential for loss of virologic response and possible resistance to delavirdine or to the pharmacologic class of NNRTIs
Adverse Reactions
Serious
- Black Box Warnings
- Cardiovascular risk associated with rapid infusion rates
- Risk of hypotension and arrhythmias with infusion rates that exceed 150mg/minute of phenytoin sodium equivalents (PE)
- Careful cardiac monitoring is needed during and after administering IV administration
- These events have also been reported at or below 150mg/minute
- Reduce infusion rate or discontinuation may be needed
- Cardiovascular collapse
- Toxic delirium
- Bradycardia
- Arrhythmias
- Exfoliative dermatitis
- Stevens-Johnson
- Toxic epidermal necrolysis
- Drug rash with eosinophilia and systemic sx
- Hepatotoxicity
- Thrombocytopenia
- Leukopenia
- Agranulocytosis
- Pancytopenia
- Anemia
- Purple glove syndrome (IV use)
Common
- Nystagmus
- Dizziness
- Pruritis
- Paresthesia
- Headache
- Somnolence
- Ataxia
- Nausea
- Tinnitus
- Rash
- Tremor
- Hypotension
- Xerostomia
- Confusion
- Blurred vision
- Taste changes
- Fever
- Injection site reaction
- Constipation
- Hypokalemia
Pharmacology
- Half-life: 15 min (phenytoin)
- Metabolism: CYP450; prodrug metabolized to phenytoin
- Excretion: urine
- Mechanism of Action: modulates neuronal voltage-dependent Na and Ca channels
See Also
References
epocrates, medscape
