Brand: SERESTO ®


FORMULATION: «collar» impregnated with insecticides/tickicides 


CHEMICAL CLASS of the active ingredient(s):


PARASITES CONTROLLED* (spectrum of activity)

  • Fleas
  • Ticks
  • Dog chewing lice (Trichodectes canis)
  • Adds in the control of sarcoptic mange mites (Sarcoptes scabiei) on dogs

* Can be slightly different in some countries: read the product label!


Collars of different sizes for cats (> 10 weeks), small dogs (≤8 kg = ≤18 lbs) and large dogs (>8 kg = >18 lbs).

Since the active ingredients are released slowly from the collar's matrix, it is not possible to calculate the exact dose that the animals are exposed to in a particular moment.


  • LD50 (acute oral) in rats: >2000 mg/kg (estimate according to MSDS)
  • LD50 (acute dermal) in rats: >2000 mg/kg (estimate according to MSDS)
  • Estimated Toxicity Class according to the WHO: III slightly hazardous (based on the LD50, learn more)

Suspected poisoning? Read the article on imidacloprid safety and/or on flumethrin safety in this site.

WARNING !!!: Never use on cats collars approved only for dogs.  Learn more about insecticide-impregnated collars and their safety.

In spring 2021 the US Environmental Protection Agency (EPA) started a review on the safety of SERESTO Collars, after ~75'000 incidents including 1'698 pet deaths had been reported since its introduction.

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance? YES, low to moderate in:

So far there are no reports on flea resistance to imidacloprid, more than 20 years after its introduction for flea control. However, fleas have developed resistance to several other insecticides (e.g. carbamates, organophosphates and pyrethroids) and are certainly capable of becoming resistant to imidacloprid as well. Experience shows that prolonged and uninterrupted use of any insecticide on fleas (including imidacloprid) bears the risk of resistance development. Imidacloprid has no effect whatsoever on ticks.

Resistance of brown dog ticks (Rhipicephalus sanguineus) and fleas to synthetic pyrethroids is not uncommon in many countries, including the USA. Since imidacloprid has no effect on brown dog ticks, protection against this tick species may be shorter than expected. For the same reason the contribution of flumethrin to the efficacy against fleas may also be weaker than expected.

There are no reports on resistance of chewing lice (Trichodectes canis) and sarcoptic mange mites (Sarcoptes scabiei) to the active ingredients in this product.

Alternatives to prevent resistance through product rotation:

*F = effective against fleas; T = effective against ticks.

These alternative products may not be available in all countries, or may not be available as collars.

Resistance of fleas and brown dog ticks to carbamates and organophosphates is not uncommon in several countries, including the USA.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?

  • Imidacloprid: GENERIC (introduced in the 1990s)
  • Flumethrin: GENERIC (introduced in the 1980s)

*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this product is marketed (maybe under another TM): basically worldwide, including the USA and the EU.
GENERIC BRANDS available? NO, in this particular composition

Click here to learn more about GENERIC vs. ORIGINAL drugs.


SERESTO is BAYER'S latest insecticide impregnated collar for dogs and cats with an impressive efficacy claim of 8 months control of fleas and ticks, including the most common ticks species that affect dogs and cats in the USA (Deer ticks or black-legged ticks Ixodes scapularis; American dog ticks Dermacentor variabilis; brown dog ticks Rhipicephalus sanguineus; and Lone Star ticks Amblyomma americanum), in the EU (Ixodes ricinus, Dermacentor reticulatus, Rhipicephalus sanguineus) and elsewhere (paralysis ticks Ixodes holocyclus; Ixodes hexagonus).

Imidacloprid is a broad-spectrum neonicotinoid insecticide introduced in the 1990s (by BAYER). It is abundantly used in pets, but very scarcely in livestock. It is massively used in agriculture and quite abundantly also against household pests.  It is an excellent flea killer, and controls chewing lice of dogs as well. But has no effect whatsoever on ticks and mites.

Flumethrin is a broad-spectrum non-systemic synthetic pyrethroid pesticide introduced in the 1980s (by BAYER). It is probably the best tickicide among all the synthetic pyrethroids, but not very powerful against fleas. It is also efficacious against mites, but not very powerful against fleas and lice, although the manufacturer claims that it has a synergistic effect with imidacloprid against fleas. It was vastly used in livestock until tick resistance became widespread in the 2000s. Usage in pets was very scarce but has significantly increased in the last years.

The label claim of 8 months protection is impressive and substantially longer than any other alternative products (spot-ons, tablets, etc.), but may not always be achieved due to resistance of brown dog ticks and/or fleas to synthetic pyrethroids.

BAYER marketed other insecticide-impregnated collars in some countries, BOLFO (with propoxur, for dogs and cats) and KILTIX (with propoxur and flumethrin, only for dogs).

Topical products (mainly spot-ons and insecticide-impregnated collars) have some advantages over systemic products (mainly tablets for oral administration and injectables):

  • Most topical products kill or sterilize the parasites before they bite and suck blood on the pet, whereas systemic products kill or sterilize the parasites only after their blood meal.
  • Topical products cannot be vomited.
  • Spot-ons and collars are very convenient to administer.
  • There is a larger choice of topical products.

But topical products have also some disadvantages:

  • Topical products contaminate the pet's hair coat and it is advisable for children and also adults to avoid contact with the pet for several days after treatment.
  • Topical products may not control parasites in some parts of the pet's body (e.g. the ears, below the tail, between the legs, etc.), whereas systemic products reach the blood-sucking parasites through the blood wherever they are.
  • Efficacy of topical products may be reduced or shortened through exposure to dirt, sun, shampooing, washing, rain, baths, etc., whereas efficacy of systemic products is independent from these factors.

For an overview and a list of the most popular pet antiparasitics for flea, tick, lice and/or mite control click here.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.