Flea and Tick Medicine Poisoning in Dogs

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Pyrethrin and Pyrethroid Toxicity in Dogs

Pyrethrin and pyrethroid are insecticides typically used for treating flea and tick infestations. Pyrethrins are derived from the Chrysanthemum cinerariaefolium plant, and from pyrethrum-related plant species. Pyrethroids are similar, but are synthetic rather than naturally based, and are 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 dog's nervous system, reversibly prolonging sodium conductance in nerve axons, and resulting in repetitive nerve discharges. These reactions occur more frequently in small dogs, and young, old, sick, or debilitated animals.

If you would like to learn more about how this condition affects cats, please visit this page in the PetMD health library.

Symptom and Types

Symptoms are often based on the type of reaction the dog 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 reaction -- excessive (hyper) salivation, paw flicking, ear twitching, mild depression, vomiting, diarrhea
  • Moderate to serious reaction -- protracted vomiting and diarrhea, depression, incoordination, muscle tremors (must be differentiated from paw flicking and ear twitching)


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


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

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

These questions are the best way to identify a list of possible irritants, since it can be difficult to detect these forms of insecticides in the dog's tissues or fluids.

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