Phenytoin

General

• Type: Anticonvulsants
• Dosage Forms: capsules 50, 100, 200, 300 125/5 mL IM/IV
• Common Trade Names: Dilantin, Phenytek

Adult Dosing

• Status Epilepticus
  • Loading dose: 15-20 mg/kg IV; if ineffective, can give 10 mg/kg IV 20 min after first dose
  • Maintenance dose: 100 mg PO/IV q 6-8hrs
  • Start 12 hours after loading dose

• Seizure disorder
  • 300-400 mg/day divided into 2-3 doses/day (Max 400 mg/dose)
  • May give 4-7 mg/kg/day divided into 2-3 doses/day
  • Consider loading dose: 15-20 mg/kg divided into 2-3 doses given 2-4 hrs apart
  • Adjust dose on response and serum levels
  • Available in extended or immediate release

• Seizure prophylaxis (neurosurgery)
  • Loading dose: 10-20 mg/kg IV in 3 doses 2-4 hrs apart (max 400 mg/dose)
  • 4-6 mg/kg/day IV divided into 2-3 doses/day
  • Can give IM route, though IV prefered
    • 100-200 mg IM q 4 hrs x 1 week
    • 150% PO dose by IM route if previously on medication

Pediatric Dosing

• Status Epilepticus
  • Loading dose: 15-20 mg/kg IV; if ineffective, can give 10 mg/kg IV 20 min after first dose
  • Max 1500 mg/day
  • Start maintenance 12 hrs after loading dose

• Seizure disorder: All doses are divided into 2-3 doses/day; always start at 5 mg/kg/day and titrate based on effect and serum levels
  • <6 mo: 5-8 mg/kg/day PO/IV
  • 6mo-4 yrs: 8-10 mg/kg/day PO/IV
  • 4-7yrs: 7.5-9 mg/kg/day PO/IV
  • 7-10 yrs: 7-8 mg/kg/day PO/IV
  • 10-16 yrs: 6-7 mg/kg/day PO/IV
  • >16 yrs use adult dosing
  • For immediate release. Extended release available for ages >7 at same dosages.

Special Populations

• Pregnancy Rating: D
• Lactation: Likely safe; limited information. Use caution.
• Renal Dosing
  • Adult: No oral loading regimen
  • Pediatric: No adjustment
• Hepatic Dosing
  • Adult: No oral loading regimen
  • Pediatric: Decrease dose, amount not defined

Contraindications

• Allergy to class/drug
• Sinus brady/SA block/2nd-3rd AV block
• Adams-Stokes syndrome
• Avoid abrupt withdrawl
• Caution:
  • CV disease
  • Hypotension
  • Alcohol use
  • HLA-B 1502 positive
  • Renal impairment
  • Hepatic impairment
  • Porphyria
  • DM
  • Thyroid disease
  • Depression
  • Elderly

Adverse Reactions

Serious

• V-Fib (IV)
• Hypotension (IV)
• CV collapse (IV)
• AV conduction disturbance (IV)
• Hepatotoxicity
• Thrombocytopenia
• Leukopenia
• Agranulocytosis
• Pancytopenia
• Megaloblastic anemia
• Stevens-Johnson syndrome
• Toxic epidermal necrolysis
• Drug rash (w/ eosinophilia)
• Tissue necrosis (IV)
• Purple glove syndrome (IV)
• Anaphylaxis
• Lymphoma
• Lupus
• Osteomalacia
• Toxic delirium
• SI
• Periarteritis nodosa
• Withdrawal seizures with abrupt discontinuation

Common

• N/V
• Rash
• Nystagmus
• Ataxia
• Slurred speech
• Dizziness
• Confusion
• Paresthesia
• Blurred vision
• Somnolence
• Constipation
• HA
• Insomnia
• Gingival hyperplasia
• Tremor
• Lymphadenopathy
• Coarse facies
• Hyperglycemia
• Osteomalacia
• Phlebitis (IV)
• Peyronie disease
• Taste change

Pharmacology

• Half-life: 7-42 hrs
• Metabolism: liver; CYP450: 2C9 and 2C19
• Excretion: bile and urine
• Mechanism of Action: effects neuronal voltage-dependent NA and CA channels

See Also

• Anticonvulsants
• Seizure levels and reloading

Sources

Epocrates Medscape