Organophosphate and carbamate insecticides

Species and toxic dose

Toxic principle

Both inhibit acetylcholinesterase. Organophosphate binding becomes permanent once the enzyme „ages" (minutes to over 40 hours, by agent); carbamate binding usually reverses within 1-2 hours.

Onset

Acute. An intermediate syndrome at about 72-96 hours (weakness, ventral flexion of the neck, possible respiratory failure); delayed polyneuropathy at 2-3 weeks.

Clinical signs

Muscarinic: salivation, lacrimation, urination, defecation, vomiting, bradycardia, bronchospasm and bronchial secretions, miosis. Nicotinic: muscle twitching, weakness, paralysis. Central: seizures, respiratory depression. Death is from respiratory failure.

Organs affected

Autonomic nervous system, neuromuscular junction, central nervous system, lungs.

Treatment principle (for veterinarians)

Skin exposure: bathe with dish detergent. Emesis only within about 1 hour and without neurological signs. Atropine, titrated to dry secretions, controls the muscarinic signs only; a small atropine test dose that produces mydriasis and tachycardia makes this poisoning unlikely. Pralidoxime helps only before the enzyme ages; its role with carbamates is debated. Benzodiazepines for seizures, methocarbamol for tremors; avoid phenothiazines and opioids; airway and ventilation support.

In the reference: Atropine, Diazepam, Midazolam

A summary of the principles in the sources, not a protocol: doses and the plan are the treating veterinarian's decision.

Notes

Organophosphates and carbamates used as veterinary ectoparasiticides are on their substance pages, with their label species and doses.

As medicines in the reference: Propoxur