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Drug interaction between phenytoin and valproic acid in a child with refractory epilepsy: a case report

Indira Valadê Carvalho1, Renata Cavalcanti Carnevale, Marília Berlofa Visacri

  • 1Department of Clinical Pathology, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.

Journal of Pharmacy Practice
|January 2, 2014
PubMed

Insights

Pediatric phenytoin toxicity occurred in a 12-year-old due to a drug interaction with valproic acid. This interaction increased free phenytoin levels, causing toxicity despite appropriate dosing.

Area of Science:

  • Pediatric Neurology
  • Clinical Pharmacology
  • Pharmacogenetics

Background:

  • Limited published data exists on phenytoin toxicity in pediatric patients.
  • Phenytoin is a commonly used antiepileptic drug, necessitating understanding of its interactions.

Observation:

  • A 12-year-old with refractory epilepsy developed phenytoin toxicity.
  • The patient was receiving concurrent treatment with phenytoin, valproic acid, and lamotrigine.
  • Serum phenytoin levels were supratherapeutic (21.92 µg/mL) despite appropriate capsule concentration and dosage.

Findings:

  • Phenytoin toxicity was observed despite appropriate drug formulation and dosage.
  • Valproic acid is implicated in increasing free phenytoin serum concentrations.
  • The mechanism involves displacement of phenytoin from plasma proteins and inhibition of its metabolism.

Implications:

  • Highlights a critical drug interaction between valproic acid and phenytoin in pediatric epilepsy management.
  • Underscores the importance of therapeutic drug monitoring for phenytoin, especially when co-administered with valproic acid.
  • Suggests potential for dose adjustments or alternative antiepileptic strategies in such cases.
Abstract

Keywords:
pediatricsphenytoinvalproic acid

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