Cardiology | Antiarrhythmic Drug Guide | Class Ib | Phenytoin

Phenytoin

IV Dose Loading: 10-15 mg/kg to maximum of 1.0 gram. 1/13 given IV bolus every 5 mins, flushed with NS. (D5W will precipitate drug in line)
Oral dose Loading: 15 mg/kg divided QID x 24 hours, then 7.5 mg/kg divided QID x 24 hours.
Additional day of 7.5 optional, depending on response and levels.
Maintenance: By age:
0-2 wk.: 4-8 mg/kg/d divided q 12 hours
Infants > 2 wk.: 8-12 mg/kg/d divided q 8 hours
Children: 5-6 mg/kg/d divided q 12 hours
Adults: 300-400 mg/day divided q 12 hours.
Levels 10-25 ug/ml
Toxicity common at > 20 ug/ml.
Kinetics Zero-order (t 1/2 depends on concentration) e.g. At high levels, additional dose increases may raise levels drastically. Average t 1/2 = 22 hours at therapeutic levels (range 7-40 hours) in adults, 8 hours at 1 month, 21 hours in full term newborns, 75 hours in prematures. Peak levels at 1.5-3 hours after oral dose of Infatabs, 4-12 hours for Kapseals.
Cautions In pregnancy, 11% incidence of fetal hydantoin syndrome, 31% incidence of lesser impairments.
Interactions Amiodarone increases levels Phenobarbital decreases levels Phenytoin potentiates warfarin anticoagulation Phenytoin decreases digoxin half-life
Preparations Dilantin suspension SHOULD NEVER BE GIVEN
Dilantin Infatabs- best absorbed 50 mg
Dilantin Kapseals: 30, 100 mg.
FDA approval in children yes

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