What Is Pyrethrin Shampoo?

by Jo Chester

Bathing a dog with pyrethrin shampoos is an easy way to control fleas.

Pyrethrin shampoos are used for insect control in dogs and cats. When used according to product labels, pyrethrin shampoos generally are safe for use once or twice during the month. On occasion, pyrethrin shampoos can be toxic even when used correctly. Small dogs are more susceptible to pyrethrin toxicity than larger ones. Prognosis for recovery from pyrethrin toxicity after treatment is fair to good.

Pyrethins and Their Sources

Six different forms of pyrethrin are used in shampoos: pyrethrin I and pyrethrin II, cinevin I and cinevin II and jasmolin I and II. These insecticides are extracted from the flowers of chrysanthemum plants grown in the Middle East, Europe, Japan and Kenya. However, regardless of the type they are listed only as “pyrethrin” on the label.

How Pyrethrins Work

Pyrethrins are for topical use and usually are applied directly to the dog. Pyrethrin shampoos typically are used to kill fleas on dogs. They also are used to kill ticks, mites, mosquitoes and lice. They affect the sodium flow out of an insect's nervous system. These compounds interfere with the nerve impulses, paralyzing the insect and eventually killing them.

Pyrethin Toxicity and Symptoms

The relative safety of pyrethrin shampoos allows them to be used on puppies and kittens, as well as on pregnant animals or animals to be bred. Occasionally, the insecticide will have an effect on a dog’s nervous system, causing the same misfiring of the nerve axons as caused in insects. Dogs may experience symptoms including allergic reactions such as hives and itching. Pyrethrins also may cause mild to severe reactions, including excessive salivation, disorientation, depression, nausea, diarrhea and muscle tremors. On rare occasions, pyrethrin toxicity may cause death. Signs of pyrethrin toxicity usually are seen within a couple of hours after applying the shampoo. There is no way of knowing in advance whether a dog will be susceptible to pyrethrin toxicity. However, the key to avoiding pyrethrin toxicity is to apply any product containing pyrethrin to your pet strictly according to the directions on the label. Most pyrethrin toxicity occurs when the amount of product applied to the animal exceeds the recommended dosage.

Treatment for Pyrethrin Toxicity

Mild symptoms can be treated by bathing the affected dog in lukewarm water using dishwashing liquid and rinsing him well. Using lukewarm water will reduce the possibility of blood vessel dilation that would increase the pyrethrin absorption. Serious symptoms must be treated by a veterinarian and usually are treated with fluid support and medication to detoxify his body. Diazepam or pentobarbital may be used to control seizures, while methocarbamol may be used to control muscle tremors.

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