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Flea and Tick Insecticide Poisoning in Cats

Reviewed by Peter Kintzer DVM, DACVIM on Tuesday, April 8, 2014
Posted December 19, 2013 in Cat Checkups & Preventive Care

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If you own a cat, this blog is a must read!

Before applying any topical flea and tick medication to your cat, pay heed.

One of the most commonly presenting emergencies I see is accidental poisoning of cats by their well-intentioned pet owners. They often put “small dog” flea medication onto their “big cat,” without appropriately consulting with their veterinarian or reading the label carefully, resulting in severe poisoning in cats.

The flea and tick topical spot-on medication most commonly implicated? Drugs from the pyrethrin and pyrethroid family. These active ingredients are commonly found in household insecticides, sprays, and topical spot-on medications. These chemicals are very safe for dogs, but should never be used for cats.

So what exactly are these chemicals? Pyrethrins are actually natural chemicals derived from the Chrysanthemum flower (commonly called the “mum”), while pyrethroids are synthetic derivatives (made by man). Common chemical names for pyrethroids include the following – note, they typically end with a “thrin.”

  • Allethrin

  • Deltamethrin

  • Cypermethrin

  • Permethrin

  • Cyphenothrin

Many of these active ingredients are used in high concentrations in flea and tick topical spot-on medications for dogs without any problem; however, in certain species (like cats and fish), this high level of a concentrated pyrethroid can result in severe poisoning.  Other sources of these chemicals include household insect sprays and topical flea sprays and shampoos; however, these are typically in very low concentrations (<1% pyrethrins or pyrethroids) and are generally safe for cats and dogs.

Kitten Getting PetUnfortunately, cats have an abnormal liver metabolism and cannot handle high concentrations of pyrethroids (or other drugs). As a result, cats develop poisoning when exposed to these chemicals.

Signs of poisoning in a cat can be severe and include the following: 

  • Agitation

  • Drooling or vomiting (typically due to grooming the product off and tasting the bitter chemical)

  • Lethargy

  • Facial twitching

  • Ear twitching

  • Hiding 

  • Walking "drunk"

  • Gastrointestinal signs (such as inappetance, anorexia, vomiting, diarrhea, etc.)

  • Muscle tremors

  • Warm to the touch (secondary to tremoring and hyperthermia)

  • Seizures

  • Death

If you accidentally applied dog flea and tick medication to your cat, contact your veterinarian, an emergency veterinarian, or an animal poison control center immediately. The sooner you treat it, the less poisonous it may be and the less expensive it may be to treat.

Treatment of pyrethrin or pyrethroid poisoning in cats includes the following:

Bathing your cat


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Justine has more than 18 years of experience in the veterinary industry and is a board-certified emergency critical care veterinary specialist and toxicologist as well as the CEO and founder of Vetgirl. She is also a founding member of IDEXX’s Pet Health Network team.