Flea and Tick Medicine Poisoning in Cats

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Pyrethrin and Pyrethroid Toxicity in Cats

Pyrethrin and pyrethroid are insecticides typically used for treating flea and tick infestations in pets. Pyrethrins are naturally-based and derived from the Chrysanthemum cinerariaefolium plant and from pyrethrum-related plant species. Pyrethroids, meanwhile, are synthetic, making them longer-lasting; these include allethrin, cypermethrin, deltamethrin, fenvalerate, fluvalinate, permethrin, phenothrin, tetramethrin, and etofenprox.

An adverse reaction to any of these toxins will affect the cat's nervous system, reversibly prolonging sodium conductance in nerve axons, which result in repetitive nerve discharges. These reactions occur more frequently in cats than in dogs due to a higher sensitivity. Also at higher risk are those that are very young, old, sick, or debilitated. Additionally, these reactions may become worse if the cat is hypothermic (low temperature).

The condition described in this medical article can affect both dogs and cats. If you would like to learn more about how it affects dogs, check out Flea and Tick Medicine Poisoning in Dogs.

Symptom and Types

Cats are especially sensitive to pyrethroids. When treated with concentrated permethrin-containing products labeled for use on dogs, they typically develop muscle tremors, incoordination, seizures, hyperthermia, and death within hours if the toxicity is not treated. Phenothrin spot-on products may result in similar but less severe clinical signs. Many of these products have been discontinued because of such common reactions. Other symptoms are based on the type of reaction the cat undergoes, such as:

  • Allergic reactions -- hives, congestion, itching, extreme sensitivity, shock, respiratory distress, death (very rare)
  • Idiosyncratic reactions -- resembles toxic reactions at much lower doses
  • Mild reactions -- excessive (hyper) salivation, paw flicking, ear twitching, mild depression, vomiting diarrhea
  • Moderate to serious reactions -- protracted vomiting and diarrhea, depression, incoordination, muscle tremors (must be differentiated from paw flicking and ear twitching)


Cats are more sensitive to these insecticides than dogs are; they have less-efficient metabolic pathways, extensive grooming habits, and long hair coats that can retain large quantities of a topically-applied product.

Cats with abnormally low body temperatures, such as after bathing, anesthesia, or sedation, are also predisposed to clinical signs of toxic poisoning.


Your veterinarian will perform a thorough physical exam on your cat, taking into account the background history of symptoms and possible incidents that might have precipitated this condition.

Questions may include: Has your cat been exposed to these substances? How much and when? Has your cat been around other animals that have been treated with them? When did the symptoms become apparent?

It can be difficult to detect these forms of insecticides in the cat's tissues or fluids. Therefore, these questions are the best way to identify a list of possible irritants.

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