Company: ZOETIS

FORMULATION: «spot-on» solution for topical administration on the back of the animals (also called pipettes, squeeze-ons, drop-ons, etc.)

ACTIVE INGREDIENT(S)*: SELAMECTIN, 120 mg/mL (= 12.0%) for dogs, 60 mg/mL (= 6%) for cats and puppies



PARASITES CONTROLLED* (spectrum of activity)

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


  • Dogs, puppies <2.5 kg bw: 1 pipette with 0.25 mL (equivalent >6.0 mg/kg selamectin)
  • Dogs, medium 2.6 to 5.0 kg bw: 1 pipette with 0.25 mL (equivalent to 12.0 - 6.0 mg/kg selamectinn)
  • Dogs, large 5.1 to 10.0 kg bw:  1 pipette with 0.50 mL (equivalent to 11.8 - 6.0 mg/kg selamectin)
  • Dogs, very large 10.1 to 20.0 kg bw: 1 pipette with 1.0 mL (equivalent to 11.9 - 6.0 mg/kg selamectin)
  • Dogs, extra large 20,1 to 40.0 kg bw: 1 pipette with 2.0 mL (equivalent to 11.9 - 6.0 mg/kg selamectin)
  • Dogs, extremely large, >40 kg bw: appropriate combination of pipettes
  • Cats, small <2.5 kg bw: 1 pipette with 0.25 mL (equivalent >6.0 mg/kg selamectin)
  • Cats, medium 2.60 to 7.5 kg bw: 1 pipette with 0.75 mL (equivalent 17.3 to 6.0 mg/kg selamectin)
  • Cats, large >7.5 kg bw: appropriate combination of pipettes

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


  • LD50 (acute oral) in rats: >5000 mg/kg (based on selamectin LD50; formulation LD50 n.a. in MSDS)
  • Estimated Toxicity Class according to the WHO: U, unlikely to present acute hazard (based on the LD50, learn more)

Suspected poisoning? Read the article on selamectin safety in this site.

WARNING !!!: Never use on cats pipettes approved only for dogs. Never use on small dogs pipettes approved for large dogs. Learn more about spot-ons and their safety.

WARNING on macrocyclic lactones. Dogs of some breeds do not tolerate macrocyclic lactones or other medicines (e.g. emodepside) that can cross the blood-brain barrier. They can suffer more or less serious adverse effects if treated at dose rates slightly higher than the recommended ones. Consequently dosing must be as accurate as possible. This is the case for Collies and related breeds, which have a mutation in the MDR-1 gene that affects the blood-brain barrier and makes it more permeable to such compounds than in dogs without this mutation. Besides Collies, other dog breeds have shown similar problems, although the MDR-1 mutation has not been confirmed in all of them. The breeds more affected by this mutation are (% frequency): Collie (70%), Long-haired Whippet (65%), Australian Shepherd (50%, also mini),  McNab (30%), Silken Windhound (30%), English Shepherd (15%), Shetland Sheepdog (15%), English Shepherd (15%), German Shepherd (10%), Herding Breed Cross (10%). Other less affected breeds are: Old English Sheepdog, Border Collie, Berger Blanc Suisse, Bobtail, Wäller. The only way to be sure that a dog is affected or not is to test for it. As more dogs are tested it is likely that the mutation is discovered in other breeds, or that the frequencies change.

WARNING on heartworm prevention. Heartworm preventatives stop development of microfilariae to adult worms but do not cure infections with adult worms. These preventative medicines are different from those curative anthelmintics that kill the adult worms. Preventatives may kill a few adult worms, but won't kill all of them. If this happens, such dead worms may block lung vessels, which can be seriously harmful, even fatal for the pet. Consequently, heartworm preventatives are usually not administered to pets that are already infected with adult worms (hence the periodic diagnostic tests), because the risk of serious complications is real. The infection has first to be treated with adequate curative anthelmintics before preventative products are administered. This is however not trivial, and also risky for the same reason. Ask your veterinary doctor.

Most heartworm preventatives contain macrocyclic lactones at a dose that kills microfilariae and ensures adequate protection for about 1 month, i.e. treatment has to be repeated monthly. In endemic regions with mild to warm climate it is recommended to treat the pets during the whole year, because mosquitoes can be infective the whole year through.

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


Risk of resistance? YES, mainly in:

  • fleas, mainly the cat flea, Ctenocephalides felis

So far there are no reports on flea resistance to selamectin, about 15 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 selamectin as well. Experience shows that prolonged and uninterrupted use of any insecticide on fleas bears the risk of resistance development.

There are reports of resistance or tolerance of heartworm microfilariae (Dirofilaria spp) to ivermectin and other macrocyclic lactones such as selamectin in the USA (mainly in the South). This has happened after about 20 years of very intensive use of such compounds there. This may happen elsewhere as well. Currently there are no other once-a-month treatments for heartworm prevention other than those containing macrocyclic lactones.

So far there are no significant problems of resistance to selamectin for mites, lice, and roundworms in dogs or cats.

Alternatives to prevent flea 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 spot-ons.

Resistance of fleas to carbamates, organophosphates and pyrethroids 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**?

  • Selamectin: GENERIC (introduced in the 1990s)

*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.

STRONGHOLD is ZOETIS' original brand with selamectin. In some countries it is marketed as REVOLUTION (e.g. EU). Patent protection for selamectin has expired, but so far no generic products have been introduced by other companies.

COUNTRIES where this product is marketed (maybe under another TM): EU, Switzerland and other countries.
GENERIC BRANDS available? NO; so far there are no generic brands available with a similar composition and spectrum of activity.

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


STRONGHOLD is ZOETIS' (formerly PFIZER Animal Health) original brand for their once-a-month flea+heartworm  spot-on with selamectin. Selamectin is the only macrocyclic lactone that controls fleas. Whereas in some countries control of Dermacentor variabilis ticks is included in the label, in the EU it is not.

Selamectinn is a macrociclic lactone introduced in the 1990s (by PFIZER → ZOETIS). It is moderately used in pets, but neither in livestock, nor in crop protection or vector control. It is the only macrocyclic lactone that controls fleas. Tick control is usually insufficient because several important species are not controlled (e.g. Amblyomma americanumIxodes spp, Rhipicephalus sanguineus, etc.

Administered about every 4 weeks, STRONGHOLD controls established flea infestations and prevents flea populations to develop in the pets environment, but only if all the dogs and cats in the same household are treated against fleas. It is also a heartworm preventative and kills some mites and gastrointestinal roundworms.

For an overview and a list of the most popular pet antiparasitics for flea & heartworm 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.

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