Brand: TRI-HEART ® PLUS
Company: MERCK ANIMAL HEALTH
FORMULATION: «tablets» for oral administration; may be chewable, flavored, coated, etc, depending on the country
- PYRANTEL (as pamoate salt)
CHEMICAL CLASS of the active ingredient(s):
- Ivermectin: MACROCYCLIC LACTONE
- Pyrantel: TETRAHYDROPYRIMIDINE
PARASITES CONTROLLED* (spectrum of activity):
- Heartworm prevention (Dirofilaria spp)
- Roundworms (Toxocara canis, Toxascaris leonina,) and hookworms (Ancylostoma caninum, A. braziliense, Uncinaria stenocephala)
USA and other countries
- Dogs ≤25 lbs. ≈ ≤11 kg bw: 1 tablet with 68 mcg ivermectin and 57 mg pyrantel (equivalent to ≥6.2 mcg/kg ivermectin and ≥5.2 mg/kg pyrantel)
- Dogs 26 to 50 lbs. ≈ 12 to 22 kg bw: 1 tablet with 136 mcg ivermectin and 114 mg pyrantel (equivalent to 11.3 to 6.2 mcg/kg ivermectin and 9.5 to 5.2 mg/kg pyrantel)
- Dogs 51 to 100 lbs. ≈ 23 to 45 kg bw: 1 tablet with 272 mcg ivermectin and 227 mg pyrantel (equivalent to 11.8 to 6.0 mcg/kg ivermectin and 9.9 to 5.0 mg/kg pyrantel)
- Dogs >100 lbs. ≈ >45 kg bw: administer the appropriate combination of tablets
* Can be slightly different in some countries: read the product label!
- LD50 (acute oral) in rats: n.a. for the tablets. 37 mg/kg for ivermectin; >5000 mg/kg for pyrantel
- Estimated Hazard Class according to the WHO: not applicable for veterinary medicines
Suspected poisoning? Read the article on ivermectin safety in this site.
Never use on cats products approved only for use on dogs, and vice-versa.
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:
- Safety for humans
- Safety for domestic animals
- Safety for the environment
- Hazard classifications of pesticides
Risk of resistance development? YES
There are reports on resistance of Ancylostoma spp to pyrantel in dogs and horses, but so far it does not seem to be widespread.
Alternatives to prevent resistance through product rotation:
There are reports of resistance or tolerance of heartworm microfilariae (Dirofilaria spp) to ivermectin and other macrocyclic lactones 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.
Learn more about resistance and how it develops.
Are the active ingredients of this product ORIGINAL* or GENERICS**?
- Ivermectin: GENERIC (introduced in the 1980s)
- Pyrantel: GENERIC (introduced in the 1960s)
*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: USA
GENERIC BRANDS available? YES, TRIHEART PLUS itself contains generic ivermectin and pyrantel.
Click here to learn more about GENERIC vs. ORIGINAL drugs.
TRI-HEART PLUS is a once-a-month heartworm preventative from MERCK ANIMAL HEALTH, a generic version of MERIAL's HEARTGARD PLUS.
Ivermectin is a broad-spectrum parasiticide effective against numerous parasites, both internal (e.g. heartworms, roundworms) and external (e.g. mites, lice). It is the most successfull parasiticide ever developed, nowadays used in thousands of brands for pets, livestock and also in agriculture.
Ivermectin was the first macrocyclic lactone introduced in the market in the early 1980s (by MSD Agvet, later MERIAL). It was a milestone and a tremendous progress that revolutionized the control of veterinary parasites. It is a broad-spectrum parasiticide effective against numerous parasites, both internal (e.g. heartworms, roundworms) and external (e.g. mites, lice) but not against tapeworms. It is the most successfull parasiticide ever developed, nowadays used in thousands of brands for pets, livestock and also in agriculture. At the administered dose in this product it is only effective as a heartworm preventative.
Immature heartworms are transmitted to pets by infected 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 dose administered ivermectin kills the migrating microfilariae in the tissues of the pets, but normally not the adult heartworms in the blood vessels.
Pyrantel is a narrow-spectrum anthelmintic belonging to the chemical class of the tetrahydropyrimidines that was introduced in the 1960s (by PFIZER → ZOETIS). It is effective against important dog worms such as the roundworms Toxocara canis and Toxascaris leonina, and the hookworms Ancylostoma caninum and Uncinaria stenocephala. Pyrantel has no effect on heartworms. It is used a lot in pets and horses but rarely in livestock. There are dozens of products for pets with generic pyrantel.
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.