Canis ISSN: 2398-2942

Phenobarbital

Synonym(s): Epiphen Phenobarbitone

Contributor(s): Kyle Braund, Laurent Garosi, Clare Rusbridge

Introduction

Name

  • Phenobarbital sodium.

Class of drug

Description

Chemical name

  • 5-ethyl-5-phenyl-2,4,6(1H,3H,5H)-pyrimidinetrione.
  • 5-ethyl-5-phenylbarbituric acid.

Molecular formula

  • C12H12N2O3.

Physical properties

  • Tablets.

Storage requirements

  • In a dry environment.
  • <25°C.

Uses

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Indications

  • Drug of first choice in management of seizures Seizures.
  • Occasionally as a tranquilizer.
  • The initial drug of choice for treating idiopathic seizure disorders Epilepsy: idiopathic in both dogs and cats and is also used adjunctively for the emergency treatment of acute seizure disorders secondary to other causes, eg strychnine, tetanus Tetanus , meningitis Meningitis.

Administration

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Pharmocokinetics

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Precautions

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Interactions

with other drugs

Drugs increasing effect of phenobarbitone

  • Chloramphenicol Chloramphenicol.
  • Central nervous system (CNS) depressants (antihistamines, narcotics, phenothiazines).
  • Phenobarbital displaced by sulfonamides and salicylates, and may increase the metabolism of many drugs.
  • Does not alter digoxin Digoxin levels.
  • Valproic acid Sodium valproate.

Drugs affected by phenobarbitone (enhanced metabolism/decreased effect)

Griseofulvin

  • Phenobarbitone may decrease absorption; avoid giving them together Griseofulvin.

Anti-epileptics

  • Barbiturates may enhance the effect of other anti-epileptics.
  • Phenobarbital reduces total plasma benzodiazepine concentration (IV and per rectum administration).
  • Serum total and free T4 concentrations may be low, ie in the range typical for dogs with hypothyroidism in dogs treated with phenobarbitol.
  • There is an increased risk of pancreatitis in dogs receiving both bromide and phenobarbitone.

Adverse Reactions

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Further Reading

Publications

Refereed papers

  • Recent references from VetMedResource and PubMed.
  • Gaskill C L, Burton S A, Gelens H C J et al(2000) Changes in serum thyroxine and thyroid-stimulating hormone concentrations in epileptic dogs receiving Phenobarbital for one year. J Vet Pharmacol Thera 23, 243-249.
  • Gieger T L, Hosgood G, Taboada J et al(2000) Thyroid functionand serum hepatic enzyme activity in dogs after phenobarbital administration. JVIM 14, 277-281.
  • Lord L K & Pedell M (1999) Owner perception of the care of long-term phenobarbital treated epileptic dogs. JSAP 40(1), 11-15.
  • Kantrowitz L B et al(1999) Serum total thyroxine, total triiodo thyronine, free thyroxine, and thyrotropin concentrations in epileptic dogs treated with anticonvulsants. JAVMA 214(12), 1804-1808PubMed.
  • Rambeck B et al(1999) Concentrations of phenobarbital in epileptic dogs on phenobarbital or primidone therapy. Kleintier Praxis 44(5), 345-354.
  • Wagner S O et al(1998) Chronic phenobarbital therapy reduces plasma benzodiazepine concentrations after intravenous and rectal administration of diazepam in the dog. J Vet Pharm Therap 21(5), 335-341.
  • Dayrell-Hart B, Steinberg S A, Van Winkle et al(1991) Hepatotoxicity of phenobarbital in dogs: 18 cases (1985-1989). JAVMA 199, 1060-1066 PubMed.

Other sources of information

  • Based on Small Animal Formulary. Tennant, Bryn (1999) 3rd edn. Cheltenham: BSAVA.

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