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I can get heartworm prevention that lasts longer than one month?

Posted 09.30.15 by Emily Lindsey

Yes… Proheart 6!


Proheart 6 was first introduced in 2001 as an every-6-month injectable heartworm prevention for dogs. It was widely adopted and used over the next 3 years, but due to an increasing number of adverse reactions, it was voluntarily withdrawn from the market in 2004. The makers of Proheart found that a solvent left over from the manufacturing process was likely the cause of the adverse reactions, so they revamped the production process and formula. In 2008, Proheart was reintroduced with restrictions on who could get it.  Only dogs under age 7 could get the drug, and it could not be given with vaccines. In 2013, after almost 5 years back on the market with safety data and tracking, the restrictions were eased so that any healthy dog over 6 months old could get the shot, and it could be given with vaccines.

How Does It Work?

The active ingredient in Proheart 6 is a drug called moxidectin. This is the same active ingredient found in the topical heartworm preventative Advantage Multi. The moxidectin in Proheart 6 is in the form of microspheres, which allow a time-released action of the drug. After injection, the microspheres get stored in subcutaneous fat and release the drug over several months. At the end of 6 months, no detectable drug is present in the dog’s body.

Who can get Proheart 6?proheart6

Healthy dogs over 6 months of age who are heartworm negative can receive Proheart 6. The product should not be given to sickly animals or those with a history of weight loss. Proheart 6 should not be given to dogs with a history of vaccine reactions or uncontrolled allergic disease (like skin allergies).

Pros to heartworm prevention that lasts longer than one month:

  • Convenience and compliance! It’s not hard to remember a monthly heartworm preventative – it’s just so EASY to forget! For people who don’t want to worry about giving a monthly prevention, Proheart 6 is a great option.
  • There is now an every-three-month oral flea and tick medication called Bravecto that helps eliminate the need for doing any once-monthly treatments.
  • Cost-wise, Proheart 6 is cheaper than many other heartworm products, though many of those monthly products also offer flea protection. When accounting for the cost of Proheart 6 + flea/tick prevention, it is comparably priced to the monthly combo options.

Cons to heartworm prevention that lasts longer than one month:

  • Only veterinarians and their trained staff members can administer Proheart 6 injections, so Fido must come in for the mid-year injection in order to stay protected.
  • Proheart 6 does not protect against as many intestinal worms as some of the monthly preventatives do.
  • Allergic reactions to Proheart 6 have been reported, and in some cases, can be very serious.


Proheart has been widely used in Australia and Asia since the product was first launched in 2001. The major difference between that version and the US version is that they only give it ONCE a year. In order to do this, they must give THREE TIMES the dose of moxidectin! That being said, some dogs can have severe reactions even to the lower-dose, US version of the drug. A typical reaction would look similar to a vaccine reaction or insect sting: puffy face, panting, hives, possible vomiting and diarrhea. These signs are often quickly reversed with an injection of Benadryl and steroids. Rarely, dogs can have more serious reactions, including shock and even death. In our practice of 15 doctors, we use Proheart 6 frequently and have had very few reactions over the past several years.

Bottom Line:

The number one reason for heartworm prevention failure is LATE or MISSED doses. Proheart 6 all but eliminates this problem. Though small risks exist, Proheart 6 is a safe, convenient, and effective way to protect your dog from the nasty and ubiquitous parasite threat that is heartworm disease.

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