Organophosphorus poisoning

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Sections available in full article Introduction, Presenting signs, Special risks (e.g. anesthetic), Pathogenesis, Etiology, Pathophysiology, Timecourse (incubation, duration), Diagnosis, Presenting problems, Client history, Clinical signs, Diagnostic investigation, Gross autopsy findings, Differential diagnosis, Treatment, Initial symptomatic treatment, Standard treatment, Monitoring, Prevention, Control, Sequelae, Prognosis, Expected response to treatment, Reasons for treatment failure, Sources, Publications, Vetstream contributor(s), Organization(s),
Contributors Dr Rosalind Dalefield BVSc PhD DipABVT DipABT
Dr Agnes Delauche DVM MRCVS DACVIM DECVN AdvCertCIM
Mr Phil Dobson BVetMed MRCVS

Introduction

  • Organophosphates (OPs) are commonly used pesticides.
  • Cause: ingestion of pesticide or following treatment for external parasites.
  • Action : organophosphates form a temporarily reversible bond with acetylcholine esterase (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.
  • Treatment : prompt action required if to be successful.
  • Prognosis : good if prompt treatment.

Diagnosis

Clinical signs

  • Exact pattern of signs - balance between parasympathetic stimulation, skeletal muscular stimulation and CNS stimulation depends on individual compound, individual animal and level of exposure.

Muscarinic signs

  • Hypersalivation.
  • Hyperlacrimation.
  • Frequent urination and defecation.
  • Noisy gastrointestinal activity.
  • Bradycardia.
  • Pupillary constriction.

Nicotinic signs

  • Muscle fasciculation.
  • Tremor.
  • Twitching.
  • Spasms, causing stiff gait or rigid stance.
  • Eventually weakness and paralysis.
CNS signs
  • Anxiety.
  • Restlessness/hyperactivity.
  • Anorexia.
  • Generalized seizures.
  • Death from asphyxiation.

Diagnosis

Differential diagnosis

  • Carbamate poisoning  Carbamate poisoning  .
  • Amitraz poisoning  Amitraz toxicity  .
  • Pyrethrum  Pyrethrum  or pyrethroid poisoning  Pyrethroid toxicosis  .
  • Tremorgenic mycotoxin poisoning.
  • Partial motor seizures.
  • Metaldehyde poisoning  Metaldehyde poisoning  .
  • Tetanus  Tetanus  .
  • Idiopathic epilepsy  Epilepsy: idiopathic  .
  • Strychnine poisoning  Strychnine toxicity  .
  • Lead poisoning  Lead toxicity  .
  • Hepatic encephalopathy  Hepatic encephalopathy  .
  • Caffeine or chocolate overdose.
  • Other causes of encephalopathies (neoplasia  Brain neoplasia  , inflammation).

Sequelae

Prognosis

  • All but the most severe cases will recover with atropine.
  • Guarded: if in coma because of wide variation in response to treatment (which depends on individual susceptibility, compound toxicity, dose, time since exposure, route of exposure).

Expected response to treatment

  • Parasympathetic signs treated with atropine should be controlled immediately, but they will recur until organophosphate is excreted.
  • Skeletal muscle excitation and CNS signs treated with pralidoxime chloride should disappear over 30 minutes following administration.

Reasons for treatment failure

  • Highly toxic compound.
  • Treatment too late.

Sources

Publications

Refereed papers

  • Fikes J D (1990)Toxicology of selected pesticides, drugs, and chemicals - organophosphorus and carbamate insecticides.Vet Clin North Am Small Anim Pract20(2), 353-367.

Other sources of information

  • Blodgett D J (2001)Organophosphate and Carbamate InsecticidesInSmall Animal Toxicology.Eds: M E Peterson and P A Talcott. Philadelphia: W B Saunders. ISBN: 0 7216 7826 2.
  • Osweiler G D (1995)Toxicology.Philadelphia: Williams and Wilkins. ISBN: 0 6830 6664 1.

Organization(s)

Veterinary Poisons Information Service (VPIS)
  • Poisons Unit, Avonley Road, London SE14 5ER, UK. Tel: 020-76359195.

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