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Oral dosing requirements for phenytoin in the first three months of life

Anita Cheng1, Brenda Banwell, Simon Levin

  • 1Department of Paediatrics, Neurology, The Hospital for Sick Children, University of Toronto, Toronto, Canada.

Journal of Population Therapeutics and Clinical Pharmacology = Journal De La Therapeutique Des Populations Et De La Pharmacologie Clinique
|July 29, 2010
PubMed

Insights

Infants require higher oral doses of phenytoin (10-20mg/kg/day) to achieve therapeutic levels. These increased doses are safe and do not cause clinical toxicity in neonates.

Area of Science:

  • Neonatal pharmacology
  • Pediatric neurology
  • Clinical toxicology

Background:

  • Physicians historically avoided long-term infant phenytoin (PHT) due to challenges in achieving therapeutic blood levels with oral doses and concerns about toxicity.
  • Conventional oral PHT doses often fail to reach effective serum concentrations in infants.

Purpose of the Study:

  • To establish the necessary oral dosage of phenytoin (PHT) for infants to attain therapeutic blood concentrations.
  • To assess the safety and absence of clinical toxicity associated with these PHT doses in neonates.

Main Methods:

  • Eight infants aged 2 weeks to 3 months received phenytoin treatment.
  • Serum concentrations of total and free phenytoin, along with the metabolite p-hydroxyphenytoin, were monitored bi-weekly.
  • Parents recorded seizure frequency and potential side effects every two weeks.

Main Results:

  • No seizures or clinical side effects were observed in the treated infants.
  • Effective oral phenytoin doses ranged from 10-20 mg/kg/day, significantly higher than adult requirements.
  • Free phenytoin constituted 8-13% of total serum concentrations, consistent with adult levels.

Conclusions:

  • Infants require oral phenytoin doses of 10-20 mg/kg/day to reach therapeutic serum levels.
  • These higher phenytoin dosages are safe for infants and do not induce clinical toxicity.
Abstract

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