Toxicity: methylxanthine in Horses (Equis) | Vetlexicon
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Toxicity: methylxanthine

ISSN 2398-2977


Synonym(s): Methylxanthine poisoning

Introduction

  • Cause: common methylxanthines, including:
    • Caffeine from coffee beans, soft drinks, guarana, and OTC medications.
    • Theophylline from tea.
    • Theobromine from cocoa beans and chocolate.
  • Signs: hyperexcitability, muscle tremors, tachycardia, sweating, polyuria and polydipsia.
  • Diagnosis: history of access to methylxanthine containing products, analytical chemistry.
  • Treatment: remove source, keep in a quiet, familiar environment, minimal stimulation, access to water, and monitoring.
  • Prognosis: complete recovery is expected, though deaths have been reported in other species.

Presenting signs

Acute presentation

Breed/Species predisposition

  • Methylxanthines are used to enhance performance in equine athletes.

Public health considerations

  • None.

Cost considerations

  • Treatment involves mostly monitoring and removing the source.
  • Affected horses recover completely.

Special risks

Pathogenesis

Etiology

  • Common methylxanthines include:
    • Caffeine from coffee beans, soft drinks, and guarana.
    • Theophylline from tea.
    • Theobromine from cocoa beans and chocolate.
  • Over the counter and prescription pharmaceuticals:
    • Theophylline.
    • Guarana extract.
    • Caffeine pills.

Predisposing factors

General

  • Performance horses are more likely to be affected.

Specific

  • Methylxanthines have been used intentionally to enhance performance.

Pathophysiology

  • Methylxanthine acts as a CNS stimulant through a variety of mechanisms:
    • Adenosine antagonism leads to:
      • Increased neuron firing.
      • Increased neurotransmitter release:
        • Acetylcholine.
        • Norepinephrine.
        • Dopamine.
        • Serotonin.
        • Gamma-aminobutyric acid (GABA).
    • Inhibition of phosphodiesterase leads to:
      • Increased cAMP.
      • Increased effect of catecholamine.
  • Clinical effects:
    • Central nervous stimulation.
    • Positive cardiac inotropy.
    • Bronchodilation.
    • Diuresis.

Timecourse

  • Variable dependent on compound.
  • Onset is usually within an hour of ingestion.
  • Recovery begins within hours of removal of the source; complete recovery within 1-3 days.

Epidemiology

  • Individual animals are affected from accidental or intentional exposure:
    • Coffee, soft drinks, or chocolate products.
    • Pharmaceutical theophylline or caffeine.
    • Guarana extracts.
  • Multiple animals have been exposed through coffee hull bedding: cocoa hull mulch is another possible source.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent reference from PubMed and VetMedResource.
  • Delfoiol D J et al (2012) Equine poisoning by coffee husk (Coffea Arabica L.). BMJ Vet Res 8 (4), 1-8 PubMed.
  • Errecalde J O, Button C & Mülders M S G (1985) Some dynamic and toxic effects of theophylline in horsesJ Vet Pharmacol Therap 8 (3), 320-327 PubMed.
  • Greene E W, Wood W E & Tobin T (1983) Pharmacology, pharmacokinetics, and behavioural effects of caffeine in horsesAm J Vet Res 44 (1), 57-63 PubMed.