Canis ISSN: 2398-2942

Paraquat poisoning

Contributor(s): Larry Thompson

Introduction

  • Non-selective herbicide.
  • Signs: caustic damage to mouth and GIT.
  • Progressive dyspnea.
  • Diagnosis: signs.
  • Treatment: no antidote.
  • Oxygen therapy contraindicated.
  • Prognosis: very poor - many animals euthanased when diagnosis made.

Pathogenesis

Etiology

  • Non-selective herbicide ingestion.
  • Used for aquatic weed control in UK.
  • Accidental poisoning rare in dogs.

Predisposing factors

General
  • Chronic exposure (months) to low levels can result in clinical poisoning.

Pathophysiology

  • A bipyridyl compound in same group as diquat.
Paraquat
  • A toxin specifically causing lung fibrosis, this is usually not appreciable radiographically due to the edema and hemorrhage that also occurs.
  • Chronic bronchitis and chronic recurrent bouts of pneumonia will cause irreversible damage to the lung interstitium.
  • Poorly absorbed orally concentrated paraquat (20%) is corrosive → gastrointestinal signs.
  • Toxicity caused by production of free radicals resulting in cell damage.
  • Paraquat is accumulated in lung tissue and renal tubular cells.
  • Results in pulmonary edema and terminal fibrosis; renal tubular necrosis.
  • Increasing respired oxygen concentration may increase free radical generation.
  • Oxygen administration may contribute to pathology of pulmonary lesions.
  • LD50: 25-150 mg/kg.
  • High dose: (100 mg/kg) → rapid multi-organ failure → death.
  • Lower dose: → gastrointestinal signs → pulmonary fibrosis → progressive respiratory failure over days/weeks → death in <6 weeks.

Timecourse

  • Peak plasma concentration of paraquat within 1 h of ingestion → acute signs.
  • If animal survives acute stage other signs develop 2-0 days after exposure.
  • Respiratory signs often delayed 2-7 days after exposure.
  • Signs are progressive for up to 3 weeks after ingestion.

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.
  • Talcott P A & Dorman D C (1997) Pesticide exposures in companion animals. Vet Med 92 (2), 167-181 VetMedResource.
  • Pond S M (1990) Manifestations and management of Paraquat poisoning. Med J Aus 152 (5), 256-259 PubMed.
  • O'Sullivan S P (1989) Paraquat poisoning in the dog. JSAP 30 (6), 361-364 VetMedResource.
  • Hart T B, Nevitt A & Whitehead A (1984) A new statistical approach to the prognostic significance of plasma paraquat concentrations. Lancet 2 (8413), 1222-1223 PubMed.

Other sources of information

  • Lorgue G, Lechenet J & Riviere A Clinical Veterinary Toxicology. Blackwell Science Ltd. pp 97-98. ISBN 0-632-03269-3.

Organisation(s)


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