Nurses Compass
Drug Guide
Fosphenytoin Sodium
Classification
Therapeutic: Anticonvulsant
Pharmacological: Prodrug of phenytoin, a hydantoin anticonvulsant
FDA Approved Indications
- Prevention and treatment of seizures associated with epilepsy, status epilepticus
Mechanism of Action
Fosphenytoin is a prodrug that is rapidly converted into phenytoin in the body. Phenytoin stabilizes neuronal membranes and decreases neuronal excitability by blocking voltage-gated sodium channels.
Dosage and Administration
Adult: Initial: 10-20 mg PE/kg IV infusion at 150 mg PE/min; adjust as needed based on response and tolerability.
Pediatric: Same as adults; dosing is weight-based, typically 5-15 mg PE/kg.
Geriatric: Use with caution, starting at lower doses due to increased sensitivity and comorbidities.
Renal Impairment: Adjust dosing based on clinical response and tolerability.
Hepatic Impairment: Use with caution; monitor closely as metabolism may be affected.
Pharmacokinetics
Absorption: Rapidly distributes after IV administration; bioavailability not applicable.
Distribution: Widely distributed across body tissues; crosses the blood-brain barrier.
Metabolism: Converted to phenytoin in the body.
Excretion: Primarily renal; small amount excreted unchanged.
Half Life: Approx. 8-15 hours for fosphenoytin, variable depending on conversion and clearance.
Contraindications
- Hypersensitivity to fosphenoytin or phenytoin.
Precautions
- Use cautiously in patients with heart block, sinus bradycardia, or Adams-Stokes syndrome.
- Monitor for hypotension, arrhythmias during IV infusion.
- Use in pregnancy only if clearly needed; potential teratogenicity known.
Adverse Reactions - Common
- Hypotension (Common)
- Headache (Common)
- Nausea/vomiting (Common)
- Rash (Common)
Adverse Reactions - Serious
- Arrhythmias, including bradycardia and ventricular fibrillation (Serious)
- Stevens-Johnson syndrome, toxic epidermal necrolysis (Rare)
- Hypersensitivity reactions, including anaphylaxis (Rare)
Drug-Drug Interactions
- Other CNS depressants, warfarin, hormonal contraceptives, carbamazepine, valproic acid.
Drug-Food Interactions
N/ADrug-Herb Interactions
N/ANursing Implications
Assessment: Monitor neurological status, vital signs, cardiac rhythm, skin for hypersensitivity, and serum levels of phenytoin if applicable.
Diagnoses:
- Risk for hypotension or arrhythmias during infusion.
- Risk for allergic reaction.
Implementation: Administer via IV infusion, keep rate within recommended limits. Monitor infusion site for phlebitis.
Evaluation: Assess for seizure control and adverse effects.
Patient/Family Teaching
- Report signs of allergic reactions, rash, or changes in heart rhythm.
- Inform that blood levels of phenytoin may need monitoring.
- Advise on avoiding other CNS depressants unless prescribed.
Special Considerations
Black Box Warnings:
- SERIOUS DERMATOLOGIC REACTIONS: Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported.
- CARDIAC ARREST, HYPOTENSION, AND OTHER OUTCOMES CAN OCCUR WHEN FOSPHENYTOIN IS ADMINISTERED IV. Proper infusion rates must be followed.
Genetic Factors: Genetic variations affecting metabolism may influence drug levels and response.
Lab Test Interference: May interfere with serum folate and vitamin levels.
Overdose Management
Signs/Symptoms: Ataxia, nystagmus, dizziness, coma, hypotension, arrhythmias.
Treatment: Discontinue drug, provide supportive care, monitor cardiac function, administer sedation if needed, and consider activated charcoal if ingestion was recent.
Storage and Handling
Storage: Store at room temperature, away from moisture and light.
Stability: Stable under recommended storage conditions.