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Heartgard Plus Chewables

Heartgard Plus Chewables by Merial Direct

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HEARTGARD® Plus Chewables for Dogs

Heartgard's Generic Name:

Ivermectin + Pyrantel pamoate

Heartgard General Description:

Ivermectin + pyrantel pamoate is a combination of 2 anti-parasitic drugs used monthly in dogs and cats to prevent heartworm infection and for the treatment and control of roundworms and hookworms. This product may be given with or without food. Chewable tablets are available in different strengths.

 What is Heartgard Plus Chewables?
  • Ivermectin and pyrantel pamoate is a combination of two anti-parasite drugs
  • Ivermectin and pyrantel pamoate is given by mouth
 Reasons for prescribing heartworm prevention Rx:
  • For heartworm prevention in dogs
  • For treatment and control of roundworms and hookworms
 What dogs/cats should not take this Heartgard Plus Chewables?
  • For use in dogs only
  • Puppies less than 6 weeks of age
  • Safe for use in Collies, Australian shepherds, Old English sheepdogs, Shelties and any of these crossbreed dogs if given the regular monthly heartworm preventative dosing level
  • Safe for use in breeding, pregnant and nursing animals
  • Pets known to have had an allergic reaction to ivermectin or pyrantel pamoate or like products

Dogs can be born with genetic mutations that impact their health. One such mutation is the MDR1 gene mutation. The MDR1 (multi-drug resistance-1) gene is responsible for the production of P-glycoprotein, which is normally responsible for transporting certain drugs out of the brain. The MDR1 gene mutation is generally found in many herding breeds, some sighthound breeds and many mixed-breed dogs.

Dogs that have a mutation in the MDR1 gene, which inhibits their ability to remove certain drugs from the brain and can lead up to a buildup of toxins, may have severe adverse reactions to some common drugs, including seizures, tremors, disorientation, blindness, lack of muscle control or even death.

Which breeds are affected?

  • Australian Shepherd  
  • Border Collie
  • Collie
  • English Shepherd
  • German Shepherd
  • Long-Haired Whippet
  • McNab
  • Miniature Australian Shepherd
  • Mixed Breed  
  • Old English Sheepdog
  • Shetland Sheepdog
  • Silken Windhound



MDR1 is the abbreviated name of a gene called Multi-Drug Resistance 1. A mutation of this gene causes sensitivity to Ivermectin and a number of other drugs. Dogs with the mutation will react to those drugs.

MDR1 : Multidrug Resistance 1 is inherited as an autosomal incomplete dominant disease. Dogs only need to inherit one copy of the MDR1 mutation to be at risk for sensitivity of certain drugs. Dogs with 2 copies of MDR1 can have more severe reactions.

Please speak with your veterinarian about testing for MDR1 if you own a breed of dog which may have MDR1 gene.

Give this medication with or without food. The medication is meant to be chewed before swallowing. It may be necessary to break the chewable into smaller pieces and hand feed as treats. Ensure that your pet consumes the entire dose.

Give medication as directed by your veterinarian. This medication is often given seasonally.

As a heartworm preventative, this medication is given once a month, beginning within a month after the pet's first exposure to mosquitoes. The medication kills the parasites acquired during the previous month. The final dose should be given within a month of the last exposure to mosquitoes.

Monthly treatment also provides effective treatment and control of roundworms and hookworms.

Ideally, give the medication on or about the same day each month.

 What if dose is missed?

If a dose is missed, give it as soon as you can. If it is time already for the next dose, skip the missed dose and go back to the normal schedule. Do not give two doses at the same time. If you miss more than 8 weeks in a row, give the drug as soon as you remember, but you should have your pet's blood tested for heartworms within 6 months (as infection may have occurred).

 What to tell/ask veterinarian before giving Heartgard?

Talk to your veterinarian about:

  • When will your pet need to be rechecked
  • Whether a blood test will need to be performed prior to treatment with this drug
  • Risks and benefits of using this drug

Tell your veterinarian about:

  • If your pet has experienced side-effects on other drugs/products
  • If your pet has experienced digestive upset now or ever
  • If your pet has experienced liver or kidney disease now or ever
  • If your pet has experienced any other medical problems or allergies now or ever
  • All medicines and supplements that you are giving your pet or plan to give your pet, including those you can get without a prescription. Your veterinarian may want to check that all of your pet's medicines can be given together.
 Heartgard Storage and Warnings:

Store in a tight, light resistant, childproof container in a cool, dry place at room temperature away from heat and direct sunlight.

People should not take this product. Keep this and all medication out of reach of children and pets. Call your physician immediately if you accidentally take this product.

 Potential side effects of Heartgard Plus Chewables:
  • When the parasites begin to die off, the animal may experience a mild hypersensitivity reaction including diarrhea
  • Self-limiting reactions may include lethargy, vomiting, diarrhea, decreased appetite, staggering, hypersalivation, convulsions within 24 hours of treatment
  • It is important to stop therapy and contact your veterinarian immediately if you think your pet has a medical problem or side effect from this product's therapy
 Can this drug be given with other drugs?
  • Yes, when ivermectin and pyrantel are used at the recommended dose, there are no contraindicated drugs. When higher doses are used, interactions may occur with amitraz dips and collars (Mitaban®, Preventic®), spinosad (Comfortis™) or diazepam or related tranquilizers.
  • If your pet experiences any unusual reactions when taking multiple medications, contact your veterinarian

Contact your veterinarian immediately if pet consumes more than the prescribed amount.

 What else should I know about Heartgard Plus Chewables?

Notify your veterinarian if your animal's condition does not improve or worsens despite this treatment.

As with all prescribed medicines, this product should only be given to the dog/cat for which it was prescribed. It should be given only for the condition for which it was prescribed.

 This is just a summary of information about ivermectin and pyrantel pamoate. If you have any questions or concerns about this product or for the condition it was prescribed, contact your veterinarian.


(Tri­Heart Plus, Heartgard, Heartgard Plus, Iverhart Plus)

Common Drug Name

Common Brand Names
Single Ingredient Products Heartgard Chewables for Dogs Heartgard Chewables for Cats
Combination Products
Heartgard Plus Chewables for Dogs, Tri­Heart Plus (for dogs), Iverhart Plus (for dogs) contain ivermectin and pyrantel pamoate

Store at room temperature in a tightly closed container, protected from light.

Dogs: Ivermectin is used as a heartworm preventive. Products with pyrantel pamoate are also used for the treatment and control of roundworms and hookworms.
Cats: Ivermectin is used as a heartworm preventive and for the removal and control of hookworms.
Ferrets: Ivermectin is used as a heartworm preventive.
Do NOT use in turtles.

Dose and Administration
Always follow the dosage instructions provided by your veterinarian. If you have difficulty giving the medication, contact your veterinarian.
Follow your veterinarian’s directions on when to give this medication. If advised to give it seasonally, remember to give it during and 1 month beyond the mosquito season, preferably on the same date each month. The tablet kills the parasites acquired during the previous month. (The tablet given May 1st treats exposures to heartworm during the month of April.)
If a dose is missed, give the tablet imme­diately and resume giving a tablet every 30 days (once a month). Contact your veterinarian regarding the need to have your pet heartworm tested in 6­7 months.
Heartgard Chewable tablets should be chewed. If you think your pet will swallow them whole, break them into pieces before giving them. Tri­Heart Plus and Iverhart Plus chewable tablets will be equally effective whether chewed or swallowed whole.
If switching from diethylcarbamazine (a once­a­day heartworm preventive) give ivermectin within 30 days of discontinuing the diethylcarbamazine.
This medication should only be given to the pet for whom it was prescribed.

Possible Side Effects
Side effects are rare at the recommended heartworm prevention dosage.
If your pet experiences an allergic reaction to the medication or to dying parasites, signs may include facial swelling, hives, scratching, sudden onset of diarrhea, vomiting, shock, seizures, pale gums, cold limbs, or coma. If you observe any of these signs, contact your veterinarian immediately.

Not for use in animals who are hypersensitive (allergic) to it.
Studies support the safety of ivermectin products in dogs, including Collies, when used as recommended by the label.
Do not use in puppies or kittens less than 6 weeks of age.
Considered to be safe to use in pregnant and lactating animals (female animals nursing their young).
Consult with your veterinarian regarding necessary physical examinations and heartworm testing necessary prior to and during treatment with heartworm medications.
Some intestinal parasites may be zoonotic (able to infect humans). Ask your veter­inarian or physician how to prevent human infection and reinfection of your pet.
Properly dispose of unused ivermectin, as it may be toxic to fish and other animals.

Drug, Food, and Test Interactions
Although there are no known drug or food interactions with this medication, consult with your veterinarian before using ivermectin with any other medications, including vitamins and supplements, since interactions may occur.

Signs of Toxicity/Overdose
Dogs: May see staggering, vomiting, diarrhea, depression, or dilated pupils.
Cats: May see agitation, vocalization, loss of appetite, dilation of pupils, staggering, tremors, blindness, head­pressing, wall­climbing, and disorientation.
Most animals recover in 2­4 weeks with supportive care. If you know or suspect your pet has had an overdose, or if you observe any of these signs, contact your veterinarian immediately.
Keep this and all other medications out of the reach of children and pets.

This information may not cover all possible uses, directions, side effects, precautions, allergic reactions, drug interactions, or withdrawal times. Always consult your own veterinarian for specific advice concerning the treatment of your pet.


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