Bad Reactions Of Cats To Flea And Tick Medications

Bad Reactions Of Cats To Flea And Tick Medications

Sep 20, 2021
24 min

A common question asked by pet owners is “can you overdose a cat on flea or tick treatment? Yes, the possibility of developing adverse reactions to flea and tick medications does exist that is why it is always recommended that cat parents should consult with the veterinarian before using any flea and tick medication on their pets.



Cats are extra-sensitive to the effects of insecticides, particularly flea and tick medications. This can be attributed to the fact that their bodies are inefficient in metabolizing the chemicals that are present in these products. The effects of overexposure can range from mild to severe, depending on the quantity of chemicals a cat is exposed to.


Bad Reactions To Oral And Spot-On Flea And Medications In Cats

  • Sensitivity to the active ingredient or the chemicals in the product
  • Residues of the product cling to their coats and are ingested during grooming
  • Hypothermia – unusually low body temperature
  • Overdosing
  • Ingestion of topical flea and tick medication
  • Failure to follow proper instructions in administration and dosaging
  • Close contact with another pet that was treated with flea and tick medication



Here are the most common flea and tick medications used in cats and how they can possibly cause bad reactions.



Pyrethrin and pyrethroid


Pyrethrin and pyrethroid are common chemicals that are used in tick and flea products. Pyrethrins are extracted from Chrysanthemum cinerariaefolium and other related species to make natural-based insecticides. On the other hand, pyrethroids are synthetic, and have a longer-lasting action.



Negative effects of pyrethrin and pyrethroid use in cats


These chemicals can cause an adverse reaction in the nervous system of cats. It affects the sodium conductance in the nerve axons leading to repetitive nerve discharges. Cats are more sensitive to the effects of pyrethrin and pyrethroid compared to dogs. This can be primarily attributed to the fact that felines have less efficient metabolic pathways. Their grooming habits and long hair coats are also important predisposing factors as these can retain large amounts of topical tick and flea products.



Kittens, senior cats, sick, or debilitated cats are also at higher risk. Cats that are hypothermic (body temperature that is below the normal level) may also develop adverse reactions. Hypothermia can occur after bathing a cat or when a cat is under anesthesia or has been sedated.



Symptoms of pyrethroid toxicity in cats


Between pyrethroids and pyrethrin, cats are extra-sensitive to the pyrethroids. When products containing permethrin are administered on cats, they usually manifest nervous symptoms, such as seizures, muscle tremors, hyperthermia, and incoordination. Death can occur within hours from the onset of toxicity symptoms if medical intervention is not given. Other symptoms that may be manifested by cats include:



  • Allergies – itching, hives, respiratory distress, shock, death may occur when the cat suffers from anaphylactic shock which is very rare
  • Drooling or hypersalivation
  • Ear twitching
  • Depression
  • Vomiting
  • Diarrhea
  • Paw flicking




The most common tick and flea medications that belong to the isoxazoline group include Bravecto, Credelio, Nexgard, and Simparica. These are available as pills, chews or spot-ons. These are mostly used in dogs. Adverse reactions to isoxazoline medications mainly involve the nervous system. Affected animals can develop seizures or have mobility difficulties as they tend to stumble as a result of muscular tremors and lack of muscle control.



The isoxazoline class of medications works by binding to chloride channels that are found in the cells of nerves and muscles. This can block the transmission of nerve impulses, causing the paralysis and eventually death of the parasite. This mechanism also occurs in mammals and some other vertebrates, but the mechanism is more potent in insects. Toxicity in mammals can develop depending on the health, physiological state, and medical history of the animal. The good news is adverse reactions to these flea and tick preparations are very rare.



If your pet is currently receiving any medication belonging to the isoxazoline group, here are important things to keep in mind:



  • If your pet has not manifested any adverse reactions, such as incoordination, seizures or muscle tremors, you can continue using the drug.
  • If your pet is displaying adverse reactions, stop using the product, and call your veterinarian.
  • If your pet has a history of seizures, you SHOULD consult your veterinarian before using any flea and tick preventative on your pet.




Organophosphates are common active ingredients in lawn and garden insecticides as well as flea and tick treatments. Overexposure to the product can lead to the manifestation of signs of toxicity. A cat can experience overexposure as a result of product misuse or when several organophosphate products are used at the same time. Organophosphates may be organic in nature, but tick and flea products that contain them are not without potential risks thus it is always important for pet owners to follow directions. Organophosphates can be absorbed rapidly in the body through the lungs, skin, and digestive tract. It interferes with the normal interaction of the nerves and muscles of the body.



Organophosphates work by inhibiting the action of two essential enzymes in the body — cholinesterases and acetylcholinesterase. These enzymes break down the neurotransmitter acetylcholine. When this happens, acetylcholine stays attached to the post-synaptic receptors of neurons, and causes continuous, unending transmission of nerve impulses to nervous tissue, muscles, and organs which is externally manifested as seizures and shaking.



Symptoms of organophosphate toxicity


  • Drooling
  • Digestive upsets — vomiting and diarrhea
  • Difficulty breathing
  • Urination problems
  • Trembling
  • Muscle twitching
  • Pupils are constricted
  • Muscle weakness
  • In severe cases of toxicity, cats can develop seizures or die as a result of overexposure




Carbamate use in cats is generally limited to the flea collars. When buying one for a pet cat, always remember to choose one that is specific for use in cats. Flea collars for dogs may contain higher amounts of the insecticide and can lead to poisoning.



Carbamates cause toxicity in the same manner as organophosphates do; by inhibiting the action of cholinesterase and acetylcholinesterase. An overdose of carbamate insecticide can trigger seizures and respiratory arrest in cats.



Carbamate toxicity can occur as a result of any of the following conditions:



  • Misuse, overuse, or using several cholinesterase-inhibiting insecticides
  • Overexposure to carbamate-containing insecticides in the immediate environment
  • Intentional application of lawn or garden insecticides on cats


How To Prevent Toxic Reactions

  • Tick and flea products that are indicated only for dogs should never be used in cats. Never use products off label. Do not assume that giving a small amount of dog product is safe for cats.
  • Proper application, including the proper dose and route of administration, can greatly reduce the possibility of adverse reactions
  • Read and follow all the directions that come with the product.
  • Keep the original packaging of the product just in case your pet may exhibit toxicity symptoms.
  • Seek immediate medical attention for your pet at the initial onset of symptoms.
  • If you have a multi-pet household, flea and tick products that are applied to dogs can affect cats or other pets in the household. If you have any concerns, do get in touch with your veterinarian or the animal poison hotline.
  • Do not assume that flea and tick products that look the same are the same.
  • Even if the products are of the same brand, never assume that cat and dog versions contain the same active ingredients.
  • Avoid combining flea or tick treatment products at the same time, like giving your cat a flea bath, using a topical flea product, and letting him wear a flea collar.

Treatment Of Flea And Tick Product Poisoning In Cats

Veterinary attention should be sought immediately when you notice any sign of an adverse reaction to a flea and tick product. Time is of the essence especially when substantial amounts of the product have been applied and ingested.



Activated charcoal


Activated charcoal is given to help cats eliminate the toxic chemicals from their body.



Bathing the cat with mild dishwashing soap


To prevent the absorption of toxic chemicals through the skin, a cat that has been exposed should be bathe using mild dishwashing soap and dried thoroughly.





Your veterinarian may choose to give prescription medication to control and/or stop the muscle tremors and seizures.



Fluid therapy


In severe cases, cats may need to be confined in the vet clinic for close monitoring and intravenous administration of fluids and electrolytes. Your cat may have to stay in the hospital for several days until there are no more symptoms and body function is back to normal. While confined, monitoring will include body temperature, blood glucose, kidney function, and other tests that the veterinarian may deem necessary.


Natural alternatives for tick and flea treatment in cats

  • Citrus oil-based sprays that contain limonene or linalool
  • Boron-based products such as disodium octaborate tetrahydrate
  • Diatomaceous earth


These natural treatment alternatives are used on house premises, indoors and outdoors especially during heavy flea infestations. Other popular natural flea repellent alternatives for tick and flea treatment in cats include:



  • Essential oils — These are never used full-strength on cats. Those that are manufactured for use in cats have already been diluted to safe levels. Popular essential oils for flea treatment in cats include geraniol oil which is extracted from geranium flowers and products that contain Neem extract. There are also natural flea powders that are made of calcium carbonate, geraniol and peppermint which can be safely used on cats and dogs as well as on your carpets, rugs, yard, and other places where flea egg or larvae may be present. Use a flea comb to distribute the powder throughout your pet’s hair coat until it is spread thoroughly on your cat’s skin. An essential-oil based flea repellent shampoo can also be an excellent way to kill fleas.


  • Natural flea collars — Most flea collars that are available commercially have been treated with chemical pesticides that have been associated with toxic reactions in pets. The good news is there are now natural flea collars that can be used in combination with other flea repellent products as your pet’s line of defense against infestation.


  • Apple cider vinegar – It isn’t likely to kill fleas but it can repel them from jumping on your pet and biting. Avoid spraying on open wounds. Make a diluted mixture of 2 parts apple cider vinegar to 1 part water.


  • Cedar chips – Place cedar chips around places where your cat spends most of the time. In heavy infestations, cedar chips can be placed outside your home and surroundings to keep fleas off. Make a natural flea collar by dabbing a drop of cedarwood oil mixed with a drop of alcohol on a bandanna and tie it around pet’s neck.


  • Rosemary – Air dry rosemary leaves and grind them into a powder. Sprinkle the powder in areas where your kitty sleeps and plays. Rosemary also has anti-inflammatory properties. Boil some leaves in water. When cool, let your pet soak in it for itch relief.


  • Aloe vera juice — it’s often mixed with cayenne pepper to make a spray solution that is applied to the cat’s hair coat. Avoid getting the solution into your cat’s eyes. The cooling effects of Aloe vera can alleviate itching and soothe sore spots. The white sap or latex of Aloe vera is toxic to cats so be sure to use only the gel.