Phenytoin (Dilantin, Di-Phen, Diphenylan, Phenytex){oral}
Fosphenytoin (Cerebyx){intravenous}

Category:

• Miscellaneous

Description:

• Anticonvulsive

Indications:

• Generalized tonic-clonic seizures, simple or complex seizures, status epilepticus

• Nonepileptic seizures associated with Reye’s syndrome or after head trauma

• Fosphenytoin- substitute for oral phenytoin when PO administration not feasible; migraines, Bell’s palsy, ventricular dysrhythmias,

• Diabetic neuropathy pain (non FDA approved)

Contraindications:

• Bradycardia, 2^nd and 3^rd degree AV block, Stokes-Adams syndrome

• Sinoatrial block

Precautions:

• Pregnancy category D (risk of congenital defects increased 2-3 times); compatible with breast feeding

• Hepatic disease

• Renal disease

• Diabetes mellitus

Adverse Reactions (Side Effects):

• CNS: ataxia, confusion, dizziness, drowsiness, fatigue, headache, insomnia, nystagmus, paresthesias, psychiatric changes, slurred speech

• CV: CV collapse (when drug administered too rapidly IV), hypotension, ventricular fibrillation

• EENT: blurred vision, diplopia, gingival hyperplasia

• GI: anorexia, constipation, hepatitis, jaundice, nausea, vomiting, weight loss

• GU: nephritis

• MEME: agranulocytosis, aplastic anemia, leukopenia, lymphadenopathy, megaloblastic anemia, thrombocytopenia

• METAB: hyperglycemia

• SKIN: alopecia, hirsutism, lupus erythematosus, rash, Stevens-Johnson syndrome  

Dosage:

NOTE: Fosphenytoin 75mg equivalent to 50mg phenytoin, after administration; the dose of IV fosphenytoin is expressed as phenytoin equivalents (PE) to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin doses.

• Adult: Phenytoin 

  • Seizures: IV loading dose 15-20 mg/kg based on recent dosing history and serum levels, followed by 100mg PO or IV every 6-8 hours; PO loading dose 1g divided 400mg, 300mg, 300mg given every 2 hours; if load not necessary, may give 100mg 3 times daily, follow levels; maintenance dose: 300mg daily or 5-6 mg/kg/day in divided doses; once dosage established may use extended capsules and dose daily

  • Neuritic pain: PO 200-400mg daily

  • Fosphenytoin:

  • Status epilepticus: IV 15-20mg PE/kg loading dose administered at 100-150mg PE/minute

  • Nonemergent and maintenance dosing: IM/IV 10-20mg PE/kg loading dose administered at a rate < or = 150mg PE/minute: maintenance 4-6mg PE/kg/day

• Child: Phenytoin

  • Seizures: IV loading dose 15-20 mg/kg in divided doses of 5-10 mg/kg; PO 5 mg/kg/day in 2-3divided doses to max 300mg daily; daily maintenance dose 4-8 mg/kg

Special considerations:

• Therapeutic range 10-20 mcg/ml; nystagmus appears at 20 mcg/ml, ataxia at 30 mcg/ml, dysarthria and lethargy at levels above 40 mcg/ml; lethal dose 2-5g

• Pro-drug: fosphenytoin rapidly converted to phenytoin in vivo: minimal activity before conversion; water soluble, thus more suitable for parenteral applications: doesn’t require cardiac monitoring; can be administered at faster rate; no IV filter required; compatible with both saline and dextrose mixtures; requires refrigeration