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Giving a dog heartworm medication is easier, safer, cheaper and more compassionate than treating a dog after they have developed heartworm disease.

All FDA-approved heartworm preventatives require a prescription, so you will need to visit your veterinarian before purchasing heartworm medicine for dogs.

Your veterinarian will assess your pet’s overall health, identify any risk factors and test for heartworm disease, all of which are necessary before starting a heartworm prevention program.

You can choose topical solutions, pills or even a shot, but which one is right for your pet? Many of the heartworm preventative options on the market also offer additional parasite protection. Talk to your vet about these points to help pick a medication:

  • The type of parasites is your dog is at risk of contracting
  • Which form of medication would be safest for your pet and your household

Here are some pros and cons for the popular options and the factors that your vet will take into account when choosing the appropriate heartworm medicine for your dog.

Topical Heartworm Prevention

Topical heartworm preventatives are applied to the skin on the back of the neck and are absorbed into the body. They are given monthly to kill immature parasites.

Advantage Multi

Advantage Multi is a topical medication that protects your pet from more than just heartworms. It also offers protection against fleas, sarcoptic mange mites, hookworms, whipworms and roundworms using the active ingredients imidacloprid and moxidectin.

It’s safe for pets 7 weeks or older and 3 pounds or heavier.


With selamectin as its active ingredient, Revolution covers fleas, sarcoptic mange mites, ear mites and some ticks (American dog tick), as well as heartworms. It’s safe for dogs over 6 weeks of age.

Precautions for Topical Heartworm Treatments

The primary issue with a topical heartworm medicine for dogs is that other pets or children may come into contact with the medication before it has fully absorbed into the skin.

Make sure that no one in the household comes into contact with the application site for at least two hours after applying these products. It can cause skin irritation or headaches and can also be very irritating if it gets in or near your eyes.

Call your doctor (or veterinarian if a pet comes into contact with it) immediately if this occurs, particularly if the product is ingested.

In a few instances, dogs have experienced vomiting, diarrhea, skin irritation or even seizures after being given topical heartworm medications. These reactions are rare, but you should report any side effects to your veterinarian immediately.

Oral Heartworm Prevention

Oral heartworm medications typically come in a chewable tablet that dogs usually see as treats. These are also given monthly.

Heartgard Plus for Dogs

Heartgard Plus is one of the most popular heartworm preventatives on the market. It uses ivermectin and pyrantel to protect dogs from heartworms as well as treat and control hookworm and roundworm infestations.

It’s easy to give, and compared to the topical options, Heartgard Plus is a very affordable option.

It can be given to dogs of any weight who are over 6 weeks of age.

Sentinel Heartworm Prevention

Sentinel uses milbemycin oxime and lufenuron to protect dogs 4 weeks and up and 2 pounds or heavier from heartworms, hookworms, whipworms and roundworms. It also breaks the flea life cycle by preventing the maturation of flea eggs.

It is more expensive than Heartgard Plus, but when you factor in the additional parasite protection it offers, it’s still quite affordable.

Overdose Concerns With Heartworm Pills

It’s very important that oral heartworm medications are kept away from pets. Since so many of these products are formulated as tasty chews (a bonus for pill-averse dogs), curious pups may eat more than they should if the package is left out where they can get to it.

The vast majority of adverse reactions to oral heartworm medications occur when pets accidentally consume more than the recommended dosage. Overdose may lead to vomiting, tremors, lack of coordination, shock and even death.

If your pet is on a very strict diet or has serious food allergies, these flavored medications could cause a flare-up of symptoms and may not be the best option. Talk with your veterinarian to figure out what will work the best for your pet.

ProHeart 6 Heartworm Prevention Shot

ProHeart 6 is an injectable heartworm medication that can protect dogs from heartworm disease for a full six months. It’s administered subcutaneously (under the skin).

If you’re looking for a “set-it-and-forget-it” approach to making sure your pet doesn’t contract heartworm disease, this is an appealing option. It’s great for pet owners who have found that they have a hard time remembering monthly meds.

Possible Risks for ProHeart 6

You should be aware that ProHeart 6 has been associated with side effects like anaphylaxis (a potentially fatal type of allergic reaction), vomiting, diarrhea, seizures, listlessness and weight loss.

These reactions appear to be more frequent in dogs with preexisting allergic diseases, when ProHeart 6 is given with vaccines, and in dogs who are sick, debilitated, underweight or experiencing weight loss. For these reasons, ProHeart 6 should only be given to healthy dogs that are at least 6 months old.

Safety Considerations for Heartworm Prevention

It’s important that dogs receive the appropriate dosage of heartworm preventative. Your vet will prescribe a treatment with the right amount of medication.

Just be sure to keep your prescription updated if your pet is still growing or has gained weight to make sure they remain protected.

While any form of heartworm prevention for puppies or adult dogs comes with some risk of side effects (as all medications do), the simple fact is that the dangers associated with heartworm disease are far more serious.

The best way to minimize adverse reactions is to work with your veterinarian to determine the ideal heartworm preventative for your dog.

By: Jennifer Coates, DVM

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Related: 4 Myths About Heartworms


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