One of the most common questions I get is “Can I use my dog’s flea medication, or can I cut down the dose of my dog’s flea medication and give it to my cat?” The answer to both of these questions is NO. The dosage of flea medication is calculated out exactly for the species it is labeled for, as well as the dose of medication. If one cuts down the dose and tries to give it to the cat (either topical or oral flea preventatives), there is no guarantee that the estimated dose applied will be correct, and overdose of smaller animals or the cat can easily occur.
Cats have unique patterns of detoxifying drugs in their livers and so they are easily affected by even slight overdoses of pesticides. Some combination flea and tick medications such as K9 Advantix or Certifect are in fact toxic to cats and should never be used. If a cat is accidentally exposed to a dog’s oral flea medication, veterinary attention should be sought immediately. If a veterinarian is not available, then local or national poison control should be called to help direct supportive therapy at home for the toxin exposure. If ingested within a few hours, vomiting can be induced with either hydrogen peroxide or ipecac, and activated charcoal administered by veterinarians to prevent further absorption and toxin exposure. If necessary, IV fluids may be needed to flush any absorbed toxin out of the system, and prevent liver or kidney organ damage.
For accidental exposure to topical pesticides, cats should be bathed in lukewarm water using mild oatmeal or other mild shampoos. I have found the homeopathic remedy Nux vomica 30c potency, given up to 3 times over a several hour period also helpful in some pets to decrease toxic reactions.