Canis ISSN: 2398-2942

Ephedrine, phenylephrine, pseudoephedrine and phenylpropanolamine toxicity

Contributor(s): Nicola Bates, Patricia Talcott

Introduction

  • Cause: unintentional overdosage or accidental ingestion, with dogs being most commonly affected.
  • Signs: CNS stimulation (agitation, hyperexcitability, tremors, seizures), tachycardia and hypertension.
  • Diagnosis: based on history and clinical signs.
  • Treatment: supportive with sedation and management of hypertension.
  • Prognosis: good, if cardiovascular and CNS signs are controlled. 

Pathogenesis

Etiology

  • Most severe cases involve phenylpropanolamine. Signs may occur at therapeutic doses or slightly less (1.9-2 mg/kg) and ingestion of >15 mg/kg often causes significant cardiovascular signs.
  • Some dogs show signs at therapeutic doses of pseudoephedrine while moderate to severe signs can occur at 5-6 mg/kg and fatalities can be seen at 10-12 mg/kg.
  • Phenylephrine Phenylephrine is less of a risk due to low oral bioavailability. 
  • There is limited information on the toxic dose of ephedrine Ephedrine. In a review of cases of a herbal supplement containing guarana (caffeine, 40 mg) and ma huang (ephedrine, 12 mg) all dogs developed signs and the doses ingested ranged from 4.4-296.2 mg/kg of guarana and 1.3-88.9 mg/kg of ma huang. The lowest fatal dose was 19.1 mg/kg of guarana and 5.8 mg/kg of ma huang.

Predisposing factors

General

  • Animals with pre-existing cardiovascular disease including hypertension or hyperthyroidism may be more at risk of severe signs. 

Specific

  • Animals with hepatic or renal impairment may have a more prolonged clinical course due to reduced clearance. 

Pathophysiology

  • Sympathomimetics have direct and indirect effects on adrenergic receptors and toxic effects are due to acute cardiovascular and central stimulant effects.
  • This results in endogenous release of catecholamines in the heart and brain causing peripheral vasoconstriction, cardiac stimulation and increased blood pressure.
  • Sympathomimetic drugs can produce a wide range of effects most of which mimic the results of excess stimulation of the sympathetic nervous system (eg effects on the heart rate and blood pressure).

Timecourse

  • Onset is generally within 1 hour but can be up to 8 hours (except for phenylephrine).
  • Duration is generally 24-48 hours but may be up to 72 hours in severe cases.

Epidemiology

  • These drugs are widely available. 
  • Phenylpropanolamine is used more commonly in older female dogs, but could be accessed by other pets.
  • Risk of exposure to decongestants may be greater during the winter when coughs and colds are more prevalent.  

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 references from PubMed and VetMedResource.
  • Ginn J A, Bentley E, Stepien R L (2013) Systemic hypertension and hypertensive retinopathy following PPA overdose in a dog. J Am Anim Hosp Assoc 49 (1), 46-53 PubMed.
  • Holding J K (2012) Phenylpropanolamine toxicosis in dogs and cats. Vet Med 107 (1), 18-19 VetMedResource.
  • Kang M-H, Park H-M (2012) Application of carvedilol in a dog with pseudoephedrine toxicosis-induced tachycardia. Can Vet J 53, 783-786 PubMed.
  • Wegenast C (2012) Phenylephrine ingestion in dogs. What’s the harm? Vet Med 107 (11), 476-478 VetMedResource.
  • Peterson K L, Lee J A, Hovda L R (2011) Phenylpropanolamine toxicosis in dogs: 170 cases (2004-2009). J Am Vet Med Assoc 239 (11), 1463-1469 PubMed.
  • Crandell J M, Ware W A (2005) Cardiac toxicity from phenylpropanolamine overdose in a dog. J Am Anim Hosp Assoc 41 (6), 413-420 PubMed.

Other sources of information

  • Hovda L R, Brutlag A G, Poppenga R H, Peterson K L (eds) (2016) Blackwell’s Five Minute Veterinary Consult Clinical Companion. Small Animal Toxicology, 2nd edition. Ames, Iowa: Wiley Blackwell.

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