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Are anti-parasite medications safe for cats?

Q: My veterinarian recommends that I treat my cat with a medication to prevent infection with heartworms, intestinal parasites and fleas. I don't understand how a product can be toxic to worms and insects but not hurt my cat. Are these medications really safe for cats?

A: You’ll be happy to know that the product you’re asking about, likely Revolution or Advantage Multi, has been approved by the Food and Drug Administration (FDA) as both effective and safe in cats.

The reason these anti-parasite medications are relatively safe for mammals is that many of them target receptor binding sites and nerve cell channels that are found in worms, insects and other invertebrates but not in mammals.

For some drugs, mammals have the receptor, but it resides in the brain, and the drug doesn’t cross the blood-brain barrier in mammals. Other drugs are absorbed by fleas, killing them before they can bite, but are not absorbed through dog or cat skin.

Drugs absorbed through the skin into the blood, like the ones we’ve been talking about, are evaluated and approved by the FDA. They are dispensed after an exam by a veterinarian, who can advise whether the medication is safe for the individual pet.

On the other hand, some chemicals that kill fleas are not absorbed into the blood and therefore don’t kill internal parasites, like heartworms and intestinal parasites. These products are regulated by the Environmental Protection Agency (EPA) and don’t require a veterinary visit or prescription.

Editor’s Note: The three most common worms that infect us cats are hookworms, roundworms and tapeworms. Here is some additional information on parasite testing.


Lee Pickett, V.M.D. practices companion animal medicine. Contact her at askdrlee@insurefigo.com.

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