FORMULATION: «tablets» for oral administration; may be chewable, flavored, coated, etc, depending on the country


CHEMICAL CLASS of the active ingredient(s): MACROCYCLIC LACTONE


PARASITES CONTROLLED* (spectrum of activity):

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


USA and other countries

  • Dogs 2 to 10 lbs ≈ 0.9 to 4.5 kg bw: 1 tablet with 2.3 mg milbemycin oxime (equivalent to 2.6 - 0.5 mg/kg milbemycin oxime)
  • Dogs 11 to 25 lbs. ≈ 5 to 11.3 kg bw: 1 tablet with 5.75 mg milbemycin oxime (equivalent to 1.2 - 0.5 mg/kg milbemycin oxime)
  • Dogs 26 to 50 lbs. 12 to 22 kg bw: 1 tablet with 11.5 mg milbemycin oxime (equivalent to 1.0 - 0.5 mg/kg milbemycin oxime)
  • Dogs 51 to 100 lbs. ≈ 23 to 45 kg bw: 1 tablet with 23 mg imilbemycin oxime (equivalent to 1.0 - 0.5 mg/kg milbemycin oxime)
  • Dogs >100 lbs. >45 kg bw: administer the appropriate combination of tablets
  • Cats 1.5 to 6 lbs  0.7 to 2.7 kg bw: 1 tablet with 5.75 mg milbemycin oxime (equivalent to 8.2 - 2.1 mg/kg milbemycin oxime)
  • Cats 6.1 to 12 lbs. ≈ 2.8 to 5.4 kg bw: 1 tablet with 11.5 mg milbemycin oxime (equivalent to 4.1 - 2.1 mg/kg mcg/kg milbemycin oxime)
  • Cats 12.1 to 25 lbs. 5.5 to 11 kg bw: 1 tablet with 23 mg milbemycin oxime (equivalent to 4.2 - 2.1 mg/kg mcg/kg milbemycin oxime)

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


  • LD50 (acute oral) in rats: n.a. for the tablets. 980 mg/kg for the a.i. milbemycin oxime
  • Estimated Hazard Class according to the WHO: not applicable for veterinary medicines

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

Never use on cats tablets approved only for use on dogs, and vice-versa. Never use on cats or small dogs tablets approved for large animals. Learn more about tablets and their safety.

WARNING 1! All heartworm preventatives contain macrocyclic lactones, (e.g. ivermectin, milbemycin oxime, moxidectin, selamectin) which must be handled very carefully on dogs. The reason is that 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 breed is affected by this mutation 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 2! 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. But preventatives may kill a few adult worms. 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 need for 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.

For these reasons, heartworm prevention should always be done under the supervision of a veterinary doctor.

Click here to learn more on heartworms.

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


Risk of resistance development? YES

There are reports on resistance of Dirofilaria heartworms to macrocyclic lactones (ivermectin, milbemycin oxime, moxidectin, selamectin etc.) in the USA, reported particularly in Louisiana. Considering the massive use of these chemical class worldwide for heartworm prevention, it wouldn't be surprising that other resistance emerges in other regions in the next years. In this region, this means that if a heartworm preventative fails to achieve the expected efficacy, chance is real that it is due to resistance. Elsewhere and for the time being, if a heartworm preventative fails to achieve the expected efficacy, chance is very high that either the product was unsuited for the control of Dirofilaria heartworms, or it was used incorrectly. However, resistance cannot be excluded.

Alternatives to prevent heartworm resistance through product rotation: Currently there are no alternative active ingredients for rotation that ensure monthly heartworm prevention: all available products belong to the macrocyclic lactones that have the same mechanisme of action.

Learn more about resistance and how it develops.


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

  • Milbemycin oxime: 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: in many countries where heartworms are endemic, including the USA, Australia, Canada, Spain, Italy, etc.
GENERIC BRANDS available? YES, rather few and not everywhere

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


INTERCEPTOR was CIBA-GEIGY'S (→ NOVARTIS → ELANCO) once-a-month heartworm preventative with milbemycin oxime introduced in the late 1980s. It was the first direct competitor to MERIAL's HEARTGARD with ivermectin, which was the first once-a-month heartworm preventative at all.

Milbemycin oxime is a broad-spectrum parasiticide effective against numerous roundworms. It is exclusively used on pets, not on livestock or agriculture.

Milbemycin oxime is a macrocyclic lactone effective against roundworms and some external parasites that was introduced in the late 1980s (by CIBA-GEIGY → NOVARTIS → ELANCO). It is exclusively used in pets, not in livestock or agriculture. As a general rule, due to a different pharmacokinetic behavior the anthelmintic effect is longer for milbemycin oxime than for ivermectin, although this strongly depends on the delivery form and the administered dose. A monthly treatment ensures adequate control of the roundworm species mentioned and prevents development of heartworm microfilariae.

Immature heartworms are transmitted to pets by mosquitoes that inject microfilariae (i.e. immature heartworms) during their blood meal. These microfilariae then migrate through the pet's tissues towards the blood vessels. At the recommended dose milbemycin oxime kills the migrating microfilariae in the tissues of the pets, but normally not the adult heartworms in the blood vessels. In contrast with ivermectin, at the therapeutic dose for heartworm prevention milbemycin oxime also controls several important parasitic roundworms (Toxocara canisToxascaris leonina), hookworms (Ancylostoma caninum) and whipworms (Trichuris vulpis) in dogs, as well as roundworms (Toxocara cati) and hookworms (Ancylostoma tubaeformae) in cats.

At higher doses milbemycin oxime is also effective against certain mites species (e.g. Pneumonyssoides caninum, Demodex canis).

Later-on NOVARTIS introduced three follow-up products (not in all the countries): SENTINELPROGRAM PLUS (with additional efficacy against fleas), MILBEMAX (with additional efficacy against tapeworms), and SENTINEL SPECTRUM (with additional efficacy against both fleas and tapeworms.

For an overview and a list of the most popular pet wormers 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.