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Strychnine toxicity

ffelis

Synonym(s): Rodenticide, mole/gopher poison


Introduction

  • Rodenticide, rat poison.
  • Signs: extensor rigidity, seizures, tremors, sensitivity to light and/or sound.
  • Diagnosis: history, clinical signs, analysis of vomit or stomach contents.
  • Treatment: symptomatic - no specific antidote.
  • Prognosis: good if seizures controlled and decontamination procedures followed.

Pathogenesis

Etiology

  • Strychnine is a plant alkaloid derived from seeds of Strychnos nux-vomica and Strychnos ignatii. These are trees native to southern Asia and northern Australia.
  • Accidental ingestion of bait containing strychnine.
  • Professional strength rodenticides typically contain > 0.5% strychnine. Baits available to the public typically contain < 0.5% strychnine.
  • Malicious use of bait.

Pathophysiology

  • Strychnine is rapidly absorbed following ingestion and the severity of signs is dependent on the amount of toxin ingested.
  • Strychnine reversibly blocks the binding of glycine, an inhibitory neurotransmitter, at postsynaptic spinal neurons.
  • This results in uncontrolled excitation of the spinal cord reflexes.
  • The extensor muscles are predominantly stimulated resulting in extensor rigidity and the classic 'sawhorse' stance.
  • Death can occur when the muscles of respiration are affected, leading to apnea and hypoxia.
  • Strychnine is metabolized by the liver to strychnine N-oxide and eliminated as hepatic metabolites. The parent compound is also eliminated in the urine.
  • The half life of strychnine is about 10 hours.
  • Dogs are more susceptible than cats. LD50 in dogs is > 0.2 mg/kg. In cats, the LD50 is > 0.5 mg/kg.
  • Ingestion of recently poisoned rodents and birds can result in relay toxicosis.

Timecourse

  • Signs typically develop within 15 minutes to 2 hours after ingestion.
  • If low levels are ingested, delayed and mild symptoms may occur.

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

Other sources of information

  • Talcott P A (2004) StrychnineClinical Veterinary Toxicology. Mosby. pp. 454-456.
  • Talcott P A (2001) StrychnineSmall Animal Toxicology. Saunders. pp 741-747.
  • Walters J M (2001) RodenticidesThe Veterinary ICU Book. Teton New Media. pp1113-1114.
  • Murphy M J (2000) CVT Update: Rodenticide ToxicosisCurrent Veterinary Therapy XIII. Mosby. pp 211-212.
  • Gfeller R W, Messonnier S P (1998) StrychnineHandbook of Small Animal Toxicology & Poisonings. Mosby. pp 248-250.
  • Osweiler G D (1996) RodenticidesToxicology. Lippincott, Williams & Wilkins. pp 284-286.

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