Company: ZOETIS

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


CHEMICAL CLASS of the active ingredient(s):


PARASITES CONTROLLED* (spectrum of activity)

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


  • Cats, small <2.5 kg bw: 1 pipette with 0.25 mL (equivalent >6.0 mg/kg selamectin and >1.0 mg/kg sarolaner)
  • Cats, medium 2.5 to 5 kg bw: 1 pipette with 0.5 mL (equivalent 12.0 to 6.0 mg/kg and selamectin and 2.0-1.0 mg/kg sarolaner)
  • Cats, large 5 to 10 kg kg bw: 1 pipette with 1.0 mL (equivalent 12.0 to 6.0 mg/kg selamectin and 2.0-1.0 mg/kg sarolaner)

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


  • LD50 (acute oral) in rats:
    • >1600 mg/kg for selamectin
    • 783 mg/kg for sarolaner
  • Estimated Toxicity Class according to the WHO: U, unlikely to present acute hazard (based on the LD50, learn more)

In September 2018 the FDA of the USA has alerted pet owners and veterinarians about potential neurological adverse events following the use of products containing isoxazolines. Some treated animals have experienced adverse events such as muscle tremors, ataxia (lack of voluntary coordination of muscle movements), and seizures. This regards all products containing isoxazolines. Most treated animals will not show such adverse drug reactions, but some may be affected.

According to the USA FDA's FOI Summary, the following Adverse Drug Reactions were recorded in clinical studies with this product:

  • Lethargy: 4.3% of treated animals
  • Skin Lesions (not associated with application site): 3.5%
  • Anorexia (lack or loss of appetite): 3.2%
  • Pruritus (itching): 2.5%
  • Hair changes at administration site (alopecia): 1.8%
  • Lesions at administration site (scabbing): 0.7%

Suspected poisoning? Read the articles on selamectin safety and/or sarolaner safety in this site.

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


Risk of resistance? LOW, mainly in:

There are reports on 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.

For the time being there are no alternative once-a-month heartworm preventatives available that are suitable for product rotation with selamectin. Macrocyclic lactones are the only compounds that provide monthly prevention and all have the same mode of action.

Fleas (mainly Ctenocephalides felis) have develop resistance to several  insecticides (e.g. carbamates, organophosphates and synthetic pyrethroids) but not yet to macrocyclic lactones or isoxazolines. Since both selamectin and sarolaner are effective againts fleas but have different modes of action, their combination makes also sense in order to prevent or at least delay flea resistance.

Learn more about resistance and how it develops.


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

  • Selamectin: GENERIC (introduced in the 1990s)
  • Sarolaner: ORIGINAL (introdced in 2015)

*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): UK and several other EU countries. in the USA and other countries marketed as REVOLUTION PLUS.
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 PLUS is ZOETIS' (formerly PFIZER Animal Health) first original brand combining selamectin with sarolaner.

Selamectin 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, vector control or against household pests. It is the only macrocyclic lactone approved for flea control. It is also effective against heartworm microfilariae, against several cat roundworms, againts lice and mites and a few tick species.

Sarolaner is a broad-spectrum insecticide and acaricide belonging to the isoxazolines introduced in 2015 (by ZOETIS). STRONGHOLD PLUS is the second product with sarolaner introduced by ZOETIS, the first one being SIMPARICA, for oral (not topical) administration to dogs. Sarolaner is effective against fleas, ticks and mites. It is ineffective against any worm species. For the time being sarolaner is used excusively in pets, not in livestock or horses. It is not used in agriculture either, nor in vector control or against household pests.

Administered about every 4 weeks, STRONGHOLD PLUS 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 will also prevent heartworm infections and control some gastrointestinal roundworms and the most important mites, lice and ticks of cats.

Both selamectin and sarolaner have a systemic mode of action, i.e. after administration they get into the blood of the host and reach the parasites everywhere in the host's body. For this reason most blood sucking parasites controlled (mainly fleas & ticks) have to bite the treated host to be killed.

STRONGHOLD PLUS is not an all-in-one spot-on although it controls the many important cat parasites: e.g. mosquitoes, tapeworms and several roundworms are not controlled. And there are other tick species in Europe that can infect cats in addition to the ones controlled by this product, e.g. Dermacentor marginatus, Dermacentor pictusHaemaphysalis spp, Hyalomma spp, etc. In fact, for the time being, there is no such an all-in-one monthly tablet or spot-on available for cats or dogs.

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.