Strychnine toxicity

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Strychnine is an alkaloid pesticide toxin used commercially for eradication of vermin. It is commonly extracted from the Strychnine tree (Strychnos nux-vomica).

Although the use of strychnine is highly regulated by government authorities[1], in developing countries it is regularly used as an intentional poisoning for urban canine population control.

Strychnine at dose between 0.5 - 1 mg/kg is a neurotoxin which acts as an antagonist of glycine and acetylcholine receptors on neuromuscular junctions in skeletal muscle fibres, causing uncontrolled fasciculation[2].

It is commonly seen in clinical practice as a result of intentional poisoning[3], and young dogs with access to outdoors appear to be more predisposed[4].

Accidental ingestion by dogs results in muscular convulsions and respiratory paralysis leading to acute death.

Clinically affected dogs usually show symptoms within 15 minutes of ingestion, including muscle rigidity, tremors, opisthotonus, regurgitation, ptyalism, mydriasis, dyspnea and cyanosis[5].

There are no characteristic necropsy lesions but sometimes, due to prolonged convulsions before death, agonal hemorrhages of heart and lungs and cyanotic congestion from anoxia may be seen. Animals dying from strychnine poisoning have rapid rigor mortis[6].

A presumptive diagnosis can be made on exposure to this chemical and clinical symptoms. A definitive diagnosis requires screening for alkaloids by liquid chromatography at reference laboratories[7].

A differential diagnosis would include mycotoxicosis and snail-bait toxicity.

Treatment usually involves aggressive intravenous fluid therapy, establishment of general anesthesia with thiopentone, use of muscle relaxants such as methocarbamol or diazepam and oxygen assistance. The prognosis is guarded in most cases, and recovery is often prolonged.

Acute renal injury is a common complication and acidification of urine with ammonium chloride may be useful for ion-trapping and urinary excretion of the alkaloid.

References

  1. Edwards WC et al (1981) Strychnine poisoning in dogs: sources and availability. Vet Med Small Anim Clin 76(6):823-824
  2. Quick MP (1982) Pesticide poisoning of livestock: a review of cases investigated. Vet Rec 111(1):5-7
  3. Calzetta L et al (2002) Incidence of intentional poisoning of dogs in the Abruzzo region of Italy. Vet Hum Toxicol 44(2):111-113
  4. Blakley BR (1984) Epidemiologic and diagnostic considerations of strychnine poisoning in the dog. J Am Vet Med Assoc 184(1):46-47
  5. Meiser H & Hagedorn HW (2002) Atypical time course of clinical signs in a dog poisoned by strychnine. Vet Rec 151(1):21-24
  6. Merck Veterinary Manual
  7. Hunter RT & Creekmur RE (1984) Liquid chromatographic determination of strychnine as poison in domestic animals. J Assoc Off Anal Chem 67(3):542-545