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Organophosphate Toxicity

Many cheap flea and tick preventive medications found in pet stores and supermarts are based with chemicals called organophosphates and organocarbamates. Organophosphates function by blocking nerve inhibition. When organophosphates are present, a nerve that is firing will continue to fire. They do this by inhibiting acetylcholinesterase, an enzyme essential for normal nerve function.

While this accomplishes the killing of fleas and ticks, organophosphate based flea and tick preventives are in a class of insecticides that most commonly cause toxicity in dogs and cats. Cats in particular, tend to be especially susceptible to organophosphate toxicity.

Signs of poisoning with one of these organophosphate based products include:

-Hypersalivation (excessive drooling)
-Depressed heart rate
-Central nervous system stimulation with hyperactivity, mania, anxiety or depression.
-Trouble Breathing

Diagnosis is based on a combination of recent history of application of an organophosphate or organocarbamate based flea and tick dip, topical, or collar, and the presence of typical clinical signs. Treatment is geared toward reversing the overstimulation of the nervous system caused by organophosphates, which can be accomplished with a drug called atropine. Atropine can be administered intravenously to hasten its reversal of clinical signs. IV fluids, anticonvulsive medication, and muscle relaxers are often helpful in stabilizing the patient.

Given the toxic nature of organophosphate based flea preventives, it is advisable to avoid them in both dogs and cats. Commonly used organophosphates and organocarbamates include dichlorvos, cythioate, diazinon, malathion, carbaryl, fenthione, methylcarbamate, and prolate. Any dip, topical, oral, or collar preventive containing any of these compounds should be avoided.
Much safer (and far more effective) flea and tick preventives include Frontline, Advantage, Advantix, and Capstar.


By: Roger L. Welton, DVM
Founder, Web-DVM
President, Maybeck Animal Hospital
Author Canine and Feline 101

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