Canis ISSN: 2398-2942

Organophosphorus insecticide poisoning

Synonym(s): Organophosphate toxicity, Organophosphate toxicosis

Contributor(s): Kyle Braund, Nicola Bates


  • Organophosphates insecticides (OPs) are commonly used pesticides.
  • Cause: ingestion of pesticide or following treatment for external parasites.
  • Action: organophosphates form a temporarily reversible bond with acetylcholinesterase (AChE) and butyrylcholinesterase (pseudocholinesterase), which becomes permanent with time.
  • Signs: cholinergic crisis (excessive parasympathetic stimulation, skeletal muscle stimulation and central stimulation) varying with the compound involved and individual susceptibility.
  • Diagnosis: history, signs, laboratory assessment.
  • Treatment: prompt action required including atropine and symptomatic support.
  • Prognosis: guarded.



  • Ingestion of liquid concentrates/granules of organophosphates/carbamate compounds (widely used for control of external parasites in dogs or control or insects in the home/garden) or from excessive skin or hair coat dusting or painting.
  • Ingestion of organophosphate insecticide-containing flea collars or cattle ear tags.


  • Organophosphate insecticides and carbamates are acetylcholine esterase enzyme inhibitors; organophosphates are irreversible inhibitors of the enzyme, whereas carbamates are reversible inhibitors of acetylcholine esterase.
  • Organophosphate insecticide inhibits the compound → temporarily reversible bond with acetylcholine esterase → permanent bond as compound ages → inhibition of action of acetylcholine esterase → build up of acetylcholine at the synapses and the neuromuscular junctions → stimulation of parasympathetic and CNS synapses and neuromuscular junctions → eventual reduction in nerve sensitivity to stimulation causing depression → central respiratory depression, bronchial fluid accumulation and bronchoconstriction → asphyxia.


  • Signs develop within minutes or hours of exposure to organophosphate.
  • Time depends on individual susceptibility, compound, route of absorption and dose.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Tse Y C, Sharp C R, Evans T (2013) Mechanical ventilation in a dog with acetylcholinesterase inhibitor toxicosis. J Vet Emerg Crit Care 23 (4), 442-446 PubMed.
  • Hooper K, Aldrich J, Haskins S C (2002) The recognition and treatment of the intermediate syndrome of organophosphate poisoning in a dog. J Vet Emerg Crit Care 12 (2), 99-103 VetMedResource.
  • Atkinson J E et al (1994) Assessment of ocular toxicity in dogs during 6 months' exposure to a potent organophosphate. J Appl Toxicol 14 (2), 145-152 PubMed.
  • Munro N B et al (1991) Cholinesterase activity in domestic animals as a potential biomonitor for nerve agent and organophosphate exposure. JAVMA 199 (1), 103-115 PubMed.
  • Popović N et al (1991) Treatment of acute dichlorvos poisoning in dogs. Acta Vet Scand 87, 347-348 VetMedResource.
  • Clemmons R M et al (1990) How do I treat? Acute and subacute organophosphate intoxication in the dog and cat. Progress in Veterinary Neurology (1), 102-103 VetMedResource.
  • Rosenberg J & Quenon S G (1988) Organophosphate toxicity associated with flea-dip products - California. Morb Mortality Weekly Rpt 37 (21), 329-330 PubMed.

Other sources of information

  • Talcott P A (2016) Organophosphorus and carbamate insectides. In: Blackwell's Five Minute Veterinary Consult. Small Animal Toxicology. 2nd edn. Hovda L, Brutlag A, Poppenga R, Petersen K (eds). Wiley-Blackwell, Ames, Iowa. pp 689-696.
  • Means C (2013) Organophosphate and carbamate insecticides. In: Peterson M E, Talcott P A Small Animal Toxicology. 3rd edn. St Louis, Missouri: Elsvier. pp 715-724.
  • Wismer T, Means C (2012) Toxicology of newer insecticides in small animals. Vet Clin Small Anim 42, 335-347.
  • Rosendale M E (2003) Disulfoton: a deadly threat to pets. Vet Med 98 (6), 466-469.
  • Braund K G (1994) Clinical syndromes in veterinary neurology. 2nd edn. Mosby-Year Book, St. Louis. pp 214-215.