Organophosphate insecticides in Pets

Organophosphate and carbamate insecticides vary a hundredfold in toxicity. Learn how to turn a label percentage into mg/kg, which signs appear first and what to do right now.

What It Is

Organophosphates (for example chlorpyrifos, diazinon, malathion, disulfoton and dichlorvos) block the enzyme acetylcholinesterase, so nerve signals keep firing. The result is a flood of secretions, muscle twitching and, in severe cases, breathing failure. Carbamates such as methomyl and carbaryl act in a similar way.

Where Pets Come Across It

Garden insecticides, systemic rose granules, ant and roach baits, older flea collars and dips, agricultural products and, in some countries, products used deliberately to poison animals. Granules mixed into fertiliser or bone meal attract dogs by smell.

Which Animals Are Affected

Dogs and cats are both affected, cats often more severely. Birds are very sensitive. Livestock are poisoned by contaminated feed or sprays.

Published Toxic Dose

There is no single threshold: toxicity varies more than a hundredfold between compounds. The Merck Veterinary Manual gives rat oral LD50 values from a few mg/kg for the most toxic compounds to several hundred mg/kg for chlorpyrifos, and very few dog or cat figures. So the calculator does not grade a dose for this page. A poison line can look up the exact active ingredient and concentration.

Signs and How Soon They Appear

Signs usually start within minutes to a few hours: drooling, watery eyes, vomiting, diarrhoea, frequent urination, pinpoint pupils, muscle twitching, stiffness and difficulty breathing. Some organophosphates cause delayed weakness days to weeks later.

What to Do Right Now

Call a poison line or emergency vet immediately with the product label to hand. If the product is on the skin or coat, avoid touching it with bare hands and ask whether to bathe your pet before travelling. Keep your pet warm and calm. Do not induce vomiting; many of these products contain solvents that are dangerous if inhaled.

Frequently Asked Questions

Sources and References

• Merck Veterinary Manual: Organophosphate Toxicosis in Animals
• Merck Veterinary Manual: Carbamate Toxicosis in Animals

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