Ingredients

• One of the most commonly used insecticides in cat flea medications, pyrethrins, are made from the flowers of chrysanthemum plants. You can find pyrethrins in flea sprays and spot-on products. Synthetic pyrethrins, called pyrethroids, include permethrin, allethrin, resmethrin, phenothrin and etofenprox. Pyrethroids work slower than pyrethrins, but last for a longer period of time. Because they don't break down as easily, pyrethroids are considered possibly more toxic than natural pyrethrins, according to PetEducation.com. Organophosphates, d-limonene, linalool and methoprene, other chemicals found in cat flea medications, may also cause toxic reactions if the cat has a sensitivity to them or you apply them incorrectly.
  
  

Reactions

• Cats do not produce the enzyme glucuronidase, which helps to detoxify substances in the body, including toxins from flea medications, according to Vetinfo. Because of the lack of this enzyme, exposure to potentially toxic ingredients in flea medications, including pyrethroids or methoprene, can cause reactions ranging from moderate to severe depending on the amount of exposure. According to the Center for Public Integrity, pyrethroid-based treatments accounted for half of the most serious reactions to flea medications reported to the Environmental Protection Agency by pet owners in 2008. Reactions to toxic substances include include weakness, dizziness, tremors, convulsions or seizures, drooling, vomiting or even death. Products applied to the skin can cause chemical burns or skin sensitivity.
  
  

Warnings

• After using any flea-control product on your cat, watch it for signs of toxicity. Never combine more than one type of flea treatment with another without first consulting with a veterinarian, as this can increase the risk of a toxic reaction. Do not use flea treatments for dogs on cats, as these treatments may contain chemicals unsafe for use on cats, warns The Humane Society of the United States. The American Society for the Prevention of Cruelty to Animals recommends avoiding permethrins, commonly used in dog flea control products, on cats. At the first signs of toxicity after you use a flea-control product on your cat, contact a veterinarian.
  
  

Considerations

• To avoid toxic reactions from flea-control medications, avoid using those found over-the-counter and instead choose products provided by a veterinarian. The UC-Davis School of Veterinary Medicine recommends using selamectin, fipronil and methoprene, imidacloprid or metaflumizone for cats, all prescription products. These products have less of a chance of causing a toxic reaction when used correctly. Follow package directions and never use these, or other products, on kittens under eight weeks of age, ill, elderly or pregnant cats to avoid causing a toxic reaction, according to The Humane Society of the United States.