Heartgard For Dogs – Ingredients & Safety

Joanne Keenan
heartgard for dogs

It's normal to be afraid of heartworm disease and to want to protect your dog. Heartgard for dogs is a popular choice among heartworm meds, so here's what you need to know. 

What Is Heartgard For Dogs?

Heartgard is a heartworm medication that contains the active ingredient ivermectin. Ivermectin eliminates the tissue stage of heartworm larvae to stop them developing into juvenile and then adult heartworms. 

You need a vet’s prescription for Heartgard for dogs. A negative heartworm test is also required before starting the medication. Note that Heartgard is not effective against microfilariae or adult heartworms, so other treatment might be needed if heartworms and/or microfilariae are found.

The manufacturer recommends the drug for all dogs including pregnant or breeding bitches, stud dogs, and puppies aged 6 weeks or more, with no minimum weight requirement.

Plain Heartgard has been discontinued so you can only buy Heartgard Plus. 

What Is Heartgard Plus For Dogs?

Heartgard Plus contains the ingredient pyrantel pamoate in addition to ivermectin. Pyrantel is a dewormer (antihelmintic) used to treat roundworms and hookworms. It works by paralyzing the neuromuscular system of intestinal worms, so they detach from the intestinal walls and are expelled from the body through feces. 

What is Ivermectin?

Ivermectin is classified as a neurotoxin. It’s commonly used as an antiparasitic medication in both animals and humans. In dogs, it’s often used “off label” to treat parasites like mites (demodectic mange, scabies, ear mites) as well as intestinal parasites like hookworms and roundworms. 

Ivermectin works by targeting the nervous systems of parasites. It disrupts the neurotransmitters to paralyze muscles. which immobilizes and kills the parasites. 

Manufacturers state that when dosed appropriately, ivermectin does not harm the host animal. 

How Does Heartgard Work?

Heartgard is used to kill heartworm larvae, immature heartworms that circulate in a dog's bloodstream. This stops them from maturing into juvenile and then adult heartworms in the heart and blood vessels. Heartworm is spread by mosquitoes that bite animals with heartworm at the microfilariae stage. 

Heartgard is recommended monthly during mosquito season, with the first dose given within a month after the first exposure to mosquitoes, and the last dose within a month of the last exposure to mosquitoes.

Some vets often recommend it year-round, even in cooler climates where there are no mosquitoes in winter. This is an extra caution that the American Heartworm Society recommends, because of the increasing prevalence of drug resistant heartworms (though it’s unclear why giving more of the drug helps with that problem). 

RELATED: How do dogs get heartworms?

Is Heartgard Safe For Dogs?

Ivermectin has been extensively studied and used in both humans and animals for various medical conditions, including treating parasites. High doses of ivermectin can be toxic to dogs and a veterinary prescription is needed to make sure your dog gets the correct dosage.

Pyrantel is said to have minimal side effects such as lack of appetite, vomiting or diarrhea. But if your dog doesn’t have intestinal parasites, you may want to ask your vet how to buy plain ivermectin, so you’re not giving unneeded dewormers every month.

RELATED: Natural ways to get rid of worms in dogs ...  

Unknown Inactive Ingredients

Another consideration is the inactive ingredients in Heartgard, which comes in a "real beef" based chew formula for dogs. The manufacturer doesn’t disclose the inactive ingredients, so some dogs could have allergic reactions to the medication. At one time, you could buy the drug in tablet form to avoid the other ingredients, but that option has been discontinued. 

Heartgard For Small Dogs

Heartgard is available in different sizes depending on the size of your dog. The smallest size is for dogs up to 25 lbs, so for very small dogs some holistic vets may suggest dosing every 45 days instead of monthly. Others suggest giving half doses. However, the manufacturer doesn’t recommend either of these adjustments and says the drug is safe for all size dogs.

Heartgard For Dogs Side Effects

As with any medication, there can be potential side effects, including … 

  • Mild Stomach Upset: Some dogs might experience vomiting, diarrhea, lethargy or  reduced appetite. These symptoms are usually temporary and subside on their own.
  • Allergic Reactions: Symptoms of an allergic reaction can include itching, hives, facial swelling or difficulty breathing. These need immediate veterinary attention.
  • Neurological Symptoms: In some cases, neurological symptoms such as tremors, disorientation, or seizures can occur. This is more likely to happen if the dog has a sensitivity to the medication or if he’s given a large overdose.

Sensitivity to ivermectin can vary greatly. Most dogs can tolerate ivermectin at certain therapeutic doses used to prevent heartworm infection and control other parasites.

But certain dog breeds (such as Collies and related breeds) have a genetic mutation called MDR1 that makes them more sensitive to ivermectin, and that can lead to severe neurological side effects, even at low doses. Ask your vet about other heartworm meds that may be safer for your dog. 

When heartworm disease progresses to a major infestation, it can cause significant health problems for dogs. You can practice a multi-step prevention program by feeding a fresh whole food diet to help support the immune system in the fight against parasites and bacteria. For some dog owners, using a heartworm medication like Heartgard for dogs might be part of that program.

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© 2024, Four Leaf Rover - The content on this website is not meant to replace veterinary advice. Please support the hard working holistic vets who make this information possible. To find a holistic or homeopathic vet near you or to find one who will do phone consultations, visit The Academy Of Veterinary Homeopathy.