Canis ISSN: 2398-2942

Methiocarb toxicity

Synonym(s): Carbamate, methiocarb, thiocarbamates, aldicarb, carbaryl.

Introduction

  • Carbamates: derived from carbamic acid, thiocarbamic acid or dithiocarbamic acid. Used as: fungicides, herbicides, insecticides and molluscicides.
  • LD50 of 25 mg/kg in the dog (Methiocarb).
  • Mechanism of poisoning similar to organophosphate poisoning.
  • Signs: vomiting, tremor and convulsions.
  • Diagnosis: history, clinical signs.
  • Treatment: atropine to effect. Control nervous signs with diazepam (valium).
    Do not administer barbiturates or other cardiorespiratory depressants.
  • Prognosis: excellent if treated early.

Pathogenesis

Etiology

  • Carbamates vary widely in their toxicity, generally they are considered relatively safe.
  • Exceptions are: aldicarb, oxamyl, methiocarb, carbofuran, isolan, methomyl, formetanate, aminocarb, cloethocarb, bendiocarb.

Pathophysiology

  • Cholinesterase action → accumulation of acetylcholine → neuromuscular blockade.
  • Death, when it occurs, is due to respiratory failure.
  • The most toxic carbamates are aldicarb (LD50 5-10 mg/kg), carbofuran (LD50 19 mg/kg).
  • Carbamates are cholinesterases → accumulation of acetylcholine.
  • Fat soluble, diffuse readily into tissues.
  • Toxicity varies according to the compound involved.
  • Incomplete blockade of acetylcholinesterase → less toxic than organophosphates.
Muscarinic effects
  • Increase in all body secretions, eg hypersalivation.
  • Vomiting and diarrhea.
  • Colic.
  • Incontinence due to relaxation of the sphincters.
  • Myosis, sometimes very prominent.
Nicotinic effects
  • Predominantly neuromuscular.
  • Muscle fasciculations.
  • Clonic spasms.
  • Weakness/paralysis.
CNS effects
  • Depression.
  • Convulsive episodes.
  • Coma.

Timecourse

  • Signs of poisoning occur soon after ingestion or exposure to the poison.
  • Death due to respiratory failure may occur within a few hours to several days (according to the compound involved).
  • Occasionally → rapidly fatal asphyxia.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

Other sources of information

  • Lorgue G, Lechenet J & Reviere A (1966) Clinical Veterinary Toxicology. pp 66-68.

Organisation(s)


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