Heartgard Plus for Dogs: Preventing Heartworm Disease and Certain Types of Worms
Key takeaways:
Heartgard Plus (ivermectin / pyrantel pamoate) is a medication that prevents heartworm disease and treats and prevents hookworms and roundworms in dogs.
The medication is given to dogs once a month as a chewable tablet. It’s rare for dogs taking Heartgard Plus to have side effects.
Heartgard Plus should only be given to your dog if they have tested negative for heartworm disease. Otherwise, they could experience a serious negative reaction to the medication.
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Table of contents
Heartworm disease is a serious condition that affects many dogs each year. Heartworm disease is transmitted when an infected mosquito bites a dog. The condition causes inflammation in the heart and lungs and can be fatal without treatment.
Heartgard Plus is one of the most common medications used to prevent heartworm disease in dogs. But is it right for your dog?
Heartgard Plus for dogs at a glance
Common names | Heartgard Plus (ivermectin / pyrantel pamoate) |
What it treats | Prevents heartworms, hookworms, and roundworms |
How it comes (forms) | Chewable tablet |
Common side effects | None |
Average cost | $50-$70 for a 6-month supply |
What is Heartgard Plus for dogs and how does it work?
Heartgard Plus is an FDA-approved medication that is given to dogs monthly to prevent heartworms, hookworms, and roundworms. Heartgard Plus is a combination of two medications: ivermectin and pyrantel.
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Ivermectin can prevent heartworm disease by killing any heartworm larvae transmitted to a dog by an infected mosquito. Pyrantel kills hookworms and roundworms by paralyzing the worms. The paralyzed worms are then expelled from the dog’s intestines.
What is Heartgard Plus used for in dogs?
Heartgard Plus is given to dogs once a month in order to prevent heartworms. As mentioned, it can also treat and prevent hookworms and roundworms.
Heartgard Plus is only active against heartworms during certain stages of their development. It doesn’t protect against mature heartworms, which is why it is important to give the medication every month as prescribed.
How is Heartgard Plus given to dogs and what is the typical dosage?
Heartgard Plus comes in a chewable beef-flavored tablet that most dogs love to eat. It’s available in three different doses, which are designed for dogs of different sizes. Ask your veterinarian about the correct dosage for your dog.
The following table includes general information about the different Heartgard Plus doses and the size of dog they’re meant to treat.
Packaging color | Dog’s weight | Medication formulation |
Blue | Up to 24 lbs | 68 mcg ivermectin, 57 mg pyrantel |
Green | 26-50 lbs | 136 mcg ivermectin, 114 mg pyrantel |
Brown | 51-100 lbs | 272 mcg ivermectin, 227 mg pyrantel |
Ask your veterinarian | Over 100 lbs | Varies (see below) |
If you have a dog over 100 lbs, your veterinarian will prescribe them the correct combination of the above chewables.
Heartgard Plus should be given to your dog every 30 days. You can set a reminder on your phone to make sure you give them the medication as directed.
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What are the common side effects of Heartgard Plus in dogs?
The good news is Heartgard Plus has been around for a long time, and it’s considered very safe for dogs. Only a small number of dogs (about 1%) experience side effects, the most common of which are vomiting and diarrhea.
Heartgard Plus can represent a choking hazard for dogs that gobble their treats whole. If your pup does this, break the tablet into pieces before giving it to them.
Dogs that are sick should be examined by a veterinarian before they are given any type of heartworm prevention, including Heartgard Plus.
What are the most serious risks of Heartgard Plus for dogs?
Less common but more serious side effects of Heartgard Plus that have been reported in dogs include:
Confusion
Dilated pupils
Drooling
Lack of coordination
Contact your veterinarian, an emergency pet hospital, or a pet poison hotline right away if your dog experiences any of these serious side effects.
Heartgard Plus and heartworm disease in dogs
Heartgard Plus should not be given to dogs that have tested positive for heartworm disease. Veterinarians require dogs to have a negative heartworm test before prescribing them Heartgard Plus.
There are two reasons for this:
Heartgard Plus cannot kill adult heartworms, so your dog will need additional treatment.
If your dog has a lot of heartworm larvae in their blood, Heartgard Plus could cause a massive die-off of larvae. This can create a shock-like reaction in your dog’s system that can be life-threatening.
Heartgard Plus, ivermectin, and the MDR1 gene
Ivermectin, one of the active ingredients in Heartgard Plus, is safe for most dogs at the correct dosage. However, some herding dog breeds have increased sensitivity to ivermectin due to a mutation in their MDR1 gene.
In dogs with this gene mutation, ivermectin can cause severe damage to the nervous system. There is a simple phrase in veterinary medicine regarding the use of ivermectin in herding breeds: White feet, don’t treat.
Herding breeds with white feet include:
Collies
Border collies
Shelties
Australian shepherds
Mini Aussies
Old English sheepdogs
Many mixed breeds with herding dog ancestry
There is a simple genetic test that can tell you if your dog has the MDR1 gene. If you have a herding breed, talk to your veterinarian about the best heartworm prevention option for your dog.
Does Heartgard Plus interact with any other dog medications?
Heartgard Plus can interact with other medications your dog may be taking, including:
Amlodipine
Azole antifungals, such as ketoconazole and itraconazole
Certain antibiotics, such as erythromycin
Chloramphenicol
Cyclosporine
Echinacea
Warfarin
Let your veterinarian know about any medications your dog is taking before they are prescribed Heartgard Plus. Don’t forget this includes any supplements or vitamins your dog takes.
What should you do if your dog misses a dose of Heartgard Plus?
Heartgard Plus is given to dogs once a month. If you miss your dog’s monthly dose by a few days, give them the medication as soon as you remember. Then, adjust their medication schedule so they get their next dose a month after you gave them the missed one.
If you forget to give your Heartgard Plus, and it’s been more than 31 days since their last dose, call your veterinarian. Your vet will be able to help you get your dog back on schedule safely. You may need to get your dog tested for heartworms before giving them the medication again.
The bottom line
Heartgard Plus (ivermectin / pyrantel pamoate) is a medication that can help prevent heartworm disease in dogs and kill hookworms and roundworms. The medication is given to dogs once a month as a chewable tablet. Your veterinarian will prescribe your dog the correct dosage of Heartgard Plus based on their weight.
Heartgard Plus is safe for most dogs when given as prescribed by a licensed veterinarian. Your veterinarian will want to make sure your dog has tested negative for heartworm disease before starting Heartgard Plus, however. This will prevent your dog from experiencing a life-threatening reaction to the medication.
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References
American Heartworm Society. (n.d.). Heartworm incidence maps.
Boehringer Ingelheim. (n.d.). FAQs about Heartgard Plus.
Boehringer Ingelheim Animal Health USA Inc. (2023). Heartgard Plus (ivermectin/pyrantel) chewables [package insert].
Boehringer Ingelheim Animal Health USA Inc. (2023). Heartgard Plus- ivermectin and pyrantel pamoate tablet, chewable [package insert]. FDA.report.
Brooks, W. (2023). Heartworm preventive comparison chart for dogs and cats. Veterinary Partner.
Pet Poison Helpline. (n.d.). Ivermectin.
VetLabel.com. (2023). Heartgard plus: Product information.
Washington State University College of Veterinary Medicine. (2023). MDR1 testing for dogs and cats.
