| Compatibility
Fluids: Sodium chloride 0.9%
Y-site: Do not mix with other drugs.
Incompatibility
Fluids: Glucose 5%, glucose 10%,
Y-site: Amino acid and lipid solutions. Do not mix with other drugs.
Stability
Diluted IV solution should be used as soon as possible. Discard unused portion.
Storage
Store below 25°C. Protect from light.
Special comments
Elimination half-life 7–42 hours depending on concentration. Half-life is longer in first 7 days of life.
Tapered dosing may be required in infants with epilepsy.
Evidence
Efficacy
Initial treatment of neonatal seizures: Phenytoin (free concentration target level 3 mg/L) compared to phenobarbital (phenobarbitone) (free concentration target level 25 mg/L) has been reported to have similar efficacy in control of electrical seizures (one RCT: LOE II).1 Phenytoin 20 mg/kg compared to phenobarbital (phenobarbitone) 20 mg/kg was reported to be less effective in controlling clinical seizures (one RCT, LOE II).2 Phenytoin was shown to only provide about a 10% to 15% increase in seizure control when given following phenobarbital (phenobarbitone) failure.1 Consider phenytoin for treatment of neonatal seizures refractory to a first-line anticonvulsant. (GOR C)
Maintenance treatment of neonatal seizures: Evidence is insufficient to guide maintenance treatment for prevention of seizure recurrence after neonatal seizures. Current recommendations include to wean to one maintenance seizure medication prior to discharge; and consider weaning all seizure medication prior to discharge if single or rare seizures and if seizure-free for at least 48--72 hours and risk of recurrence not felt to be unusually high.3
Recommended dosing is phenytoin 15--20 mg/kg IV, followed by 4--10 mg/kg IV, daily in 2 to 3 divided doses with close monitoring of plasma phenytoin concentrations. Inject slowly at a rate not exceeding 1 mg/kg/min. Continuous monitoring of the electrocardiogram and blood pressure is essential.4 (GOR B)
Side effects: The incidence of side effects is unclear. Reported side effects (12.5%) from a loading dose included respiratory depression, bradycardia, oxygen desaturation, drowsiness, vomiting, pyrexia, twitching and hypotension.5 Reported side effects from maintenance treatment (all age groups) include gastrointestinal side effects (abdominal pain, nausea and vomiting); drowsiness/tiredness/fatigue/sedation; rash; decreased libido or impotence; motor disturbance (including ataxia, incoordination, nystagmus, tremor); dysmorphic and idiosyncratic side effects (gum hypertrophy, hirsutism, acne, other skin problems) and cognitive side effects and impairments, including slowing of mental function, inattention, psychomotor retardation, depression and memory problems.6
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