Usual Adult Dose for Seizures:
Oral (except suspension) Loading dose: Only when indicated for inpatients.
1 g orally divided in 3 doses (400 mg, 300 mg, 300 mg) given at 2 hour intervals. Then normal maintenance dosage started 24 hours after loading dose.
Initial dose: 100 mg extended release orally 3 times a day.
Maintenance dose: 100 mg orally 3 to 4 times a day. If seizure control is established with divided doses of three 100 mg capsules daily, once-a-day dosage with 300 mg of extended release phenytoin sodium may be considered. Alternatively, the dosage may need to be increased up to 200 mg orally 3 times a day, if necessary.
Suspension: Patients who have received no previous treatment may be started on 125 mg (one teaspoonful) of the suspension three times daily, and the dose is then adjusted to suit individual requirements. An increase to five teaspoonfuls daily may be made, if necessary.
IV: Do not exceed the infusion rate of 50 mg/min.
Loading dose: 10 to 15 mg/kg IV slowly.
Maintenance dose: 100 mg IV every 6 to 8 hours.
IM: Avoid the IM route due to erratic absorption.
Usual Adult Dose for Arrhythmias:
Loading Dose:
1.25 mg/kg IV every 5 minutes. May repeat up to a loading dose of 15 mg/kg, or
250 mg orally 4 times a day for 1 day, then 250 mg twice daily for 2 days
Maintenance Dose:
300 to 400 mg/day orally in divided doses 1 to 4 times a day
Usual Adult Dose for Status Epilepticus:
IV:
Loading dose: Manufacturer recommends 10 to 15 mg/kg by slow IV administration (at a rate not exceeding 50 mg/minute). Alternatively, generally accepted guidelines suggest 15 to 20 mg/kg by slow IV administration (at a rate not exceeding 50 mg/minute).
Maintenance rate: 100 mg orally or IV every 6 to 8 hours
Maximum rate: 50 mg/minute
Maintenance dose: IV or Oral: 100 mg every 6 to 8 hours
Usual Adult Dose for Neurosurgery:
Neurosurgery (prophylactic): 100 to 200 mg IM at about 4 hour intervals during surgery and the immediate postoperative period. (Note: While the manufacturer recommends IM administration, this route may cause severe local tissue destruction and necrosis. Some clinicians recommend the use of fosphenytoin if IM administration is necessary.) If IM administration is not necessary, accepted protocol has been 100 to 200 mg IV at about 4 hour intervals during surgery and the immediate postoperative period.
Usual Pediatric Dose for Seizures:
Status Epilepticus: Loading Dose:
Infants, Children: 15 to 20 mg/kg IV in a single or divided doses
Anticonvulsant: Loading Dose:
All ages: 15 to 20 mg/kg orally (based on phenytoin serum concentrations and recent dosing history). The oral loading dose should be given in 3 divided doses administered every 2 to 4 hours.
Anticonvulsant: Maintenance Dose:
(IV or oral) (Note: May initially divided daily dose into 3 doses/day, then adjust to suit individual requirements.)
Less than or equal to 4 weeks: Initial: 5 mg/kg/day in 2 divided doses
Usual: 5 to 8 mg/kg/day IV in 2 divided doses (may require dosing every 8 hours).
Greater than or equal to 4 weeks: Initial: 5 mg/kg/day in 2 to 3 divided doses
Usual: (may require up to every 8 hour dosing)
6 months to 3 years: 8 to 10 mg/kg/day
4 to 6 years: 7.5 to 9 mg/kg/day
7 to 9 years: 7 to 8 mg/kg/day
10 to 16 years: 6 to 7 mg/kg/day
Usual Pediatric Dose for Arrhythmias:
Greater than 1 year:
Loading Dose: 1.25 mg/kg IV every 5 minutes. May repeat up to a loading dose of 15 mg/kg.
Maintenance Dose: 5 to 10 mg/kg/day orally or IV in 2 to 3 divided doses
 Detailed Phenytoin dosage information
What happens if I miss a dose?
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phenytoin can be fatal. Overdose symptoms may include twitching eye movements, slurred speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, feeling light-headed, fainting, and slow or shallow breathing.
