Imidacloprid/Flumethrin (Seresto) for Dogs and Cats

Medically Reviewed by Joshua Conrad, PharmD on October 08, 2024
Written by Kathleen Claussen, DVM
4 min read

Imidacloprid/flumethrin (Seresto) is a combination medicine in a collar your dog can wear to help control fleas, ticks, and chewing lice. Your cat can wear the same collar to help with fleas and ticks. The two medicines work together in the collar that dogs and cats can wear for up to eight months.

Imidacloprid and flumethrin are very well-tolerated by dogs and cats, puppies as young as 7 weeks old, and kittens as young as 10 weeks old. There’s little risk of overdose, severe side effects, or drug interactions. Once pets start wearing the collar, the medicine starts to repel and kill adult fleas in 24 hours, and it kills attached ticks in 48 hours. 

You can buy the collar without a prescription.

Imidacloprid/flumethrin comes in a collar your cat or dog wears around their neck. The collar slowly releases the medication to kill fleas, ticks, some lice, and some mites. 

Two sizes are available for dogs and puppies, and one size for cats and kittens. Be sure to choose the proper size and fit (two fingers should fit between your pet’s neck and the collar). Check the fit often and readjust as needed. 

The collar is water resistant, but you should replace it every five months if your dog (or cat) swims or is bathed more than once a month. For best results, all cats and dogs in your house should wear a collar to keep fleas and ticks from coming back.

Always follow your veterinarian’s directions for giving medicines to animals. Tell them about any other medicines, vitamins, supplements, or herbal therapies that you’re giving your dog or cat. Talk to your veterinarian before stopping any pet medicines. 

There are several benefits of imidacloprid/flumethrin:

  • It’s approved for use in dogs, puppies, cats, and kittens.
  • It treats and prevents fleas on dogs and cats for as long as eight months.
  • Fleas don’t have to bite your dog or cat to die.
  • It helps control several types of ticks for up to four months.
  • It’s very easy to use.
  • It starts to work within 48 hours.
  • There’s a very low risk of drug interactions or side effects. 

You and your veterinarian should monitor your dog or cat for improvement, like fewer fleas and ticks, and less itching and scratching. Check the fit of the collar often to make sure it’s not too loose or too tight. Check the fit more often on growing puppies and kittens.

If you’re using imidacloprid/flumethrin collars for mites, your veterinarian will likely do a follow-up skin test or scraping.

Don’t use imidacloprid/flumethrin collars on dogs or cats that are allergic. Don’t put the collar on puppies less than 7 weeks old, or on kittens less than 10 weeks old. Use it with caution in cats or dogs that are underweight, old, or weak, or those that are breeding, pregnant, or nursing.

Side effects of imidacloprid/flumethrin collars are rare but might include: 

  • Redness or itching at the neck
  • Slight fur loss
  • Mild skin reactions
  • Excessive drooling if there is oral contact

 Symptoms of allergic reactions are rare and might include:

  • Irregular breathing 
  • Rash 
  • Fever 
  • Swelling around the face

Allergic reactions to the collar are rare, and it may take time for symptoms to appear. If your dog or cat shows any of these signs, remove the collar and call your vet right away.

If you think your pet is having a serious side effect, call your veterinary clinic right away. If it is outside of regular office hours, contact a local emergency veterinary hospital or an animal poison control center. Note that fees may apply for emergency consultation.

You can reach the ASPCA Animal Poison Control Center at 888-426-4435 or the Pet Poison Helpline at 855-764-7661.

Don’t use an imidacloprid/flumethrin collar if your pet is taking any other flea and tick preventive medicine. Imidacloprid/flumethrin usually doesn’t interact with other medicines in dogs and cats, but using multiple medicines can sometimes change how your pet’s medicines work. Always tell your veterinarian about any prescription or over-the-counter medicines, vitamins/minerals, herbal products, and other supplements that your pet is using.

Keep imidacloprid/flumethrin and the product packaging out of the reach of children. Wash your hands after you put the collar on your pet, and don’t touch the collar if you’re allergic. 

Avoid touching the collar to your eyes, skin, or clothes. 

It’s unlikely your dog or cat will overdose on imidacloprid/flumethrin. But if they swallowed some of the medicine (for instance by chewing or eating the collar), call your veterinarian or veterinary emergency clinic right away.

If you missed changing the collar at the scheduled time, put a new one on as soon as you remember. Don’t use dog collars on cats or cat collars on dogs.

Store the collar in its original container at room temperature, protected from moisture and light, until you’re ready to use it.