Study compares heartworm disease treatments

In a recent study, an extended-release injectable moxidectin protocol (MOX) has shown promise as an alternative heartworm treatment for dogs. Investigators found MOX is equally effective to a 3-dose melarsomine protocol (AHS-3) recommended by the American Heartworm Society (AHS) for clearing heartworm infections in dogs.¹

The MOX protocol consists of a subcutaneous injection of moxidectin 0.5 mg/kg on days 0 and 180; doxycycline 10 mg/kg twice a day on days 0 to 30; and prednisone 0.5 mg/kg twice a day on days 0 to 7, once a day on days 8 to 14, and once every 48 hours on days 15 to 30. The AHS-3 protocol comprises melarsomine 2.5 mg on days 60, 90, and 91, plus the doxycycline and prednisone regimen with monthly heartworm prevention suggested by the AHS.¹

Lead investigator Ta-Li Lu, DVM, DAiCVIM (Cardiology), a practitioner and superintendent at Chuan Animal Hospital in Taipei, Taiwan, noted that although there is a “really good protocol from AHS” for treating heartworm disease, there are sometimes issues that cause the treatment to become unavailable, such as a lack of stock. “I do think we need a second option. Right now, moxidectin plus doxycycline is a promising one,” he said in a dvm360 interview at the 2025 American College of Veterinary Internal Medicine Forum in Louisville, Kentucky.

According to the FDA, heartworm infection is a serious parasitic condition that causes lung disease, heart failure, and other organ damage in canine and feline pets, as well as other animals. Spread through bites from host mosquitoes, the heartworm (Dirofilaria immitis) matures, mates, and produces offspring while living inside a dog or other animal.²

Heartworm disease in the US is most common along the Gulf and Atlantic coasts, as far north as New Jersey, as well as the Mississippi River and its tributaries. However, all 50 states have reported heartworm infections.²

The study in Taiwan enrolled 24 client-owned dogs that were positive for heartworm antigen. These canines were randomly assigned to 2 groups, each comprising 12 dogs. They received heartworm antigen/microfilaria tests, blood work, thoracic radiographs, electrocardiogram, and echocardiography on days 0 and 90 and monthly after day 90.¹

Treatments were considered effective when dogs tested negative for heartworm antigen. In each of the 2 study groups, 11 dogs achieved antigen negativity within 360 days of treatment.¹ “The time they turn to negative is similar within 2 groups,” Lu said.

During the study, 1 dog died after receiving 3 injections, according to Lu. However, the cause of death is unknown.

The investigators would continue to recommend the AHS-3 protocol, Lu said, but the MOX protocol could be an effective alternative. Additionally, clients may find the MOX protocol beneficial in other ways.

“The benefit is [MOX] makes their life easier,” Lu said. “So for the new protocol, they only got 1 injection and 1 month of dosing cycling—that's all, basically—and then a 6-month recheck and, if it's still possible, 1 injection more. Then it's gone. So, they don't have to take a lot of medicine…I think the moxidectin [injection] is more tolerable, too. We don't see any severe [adverse] effect after the injection.”

References

1. Lu TL, Atkins C, Change CY, et al. Comparable efficacy of injectable moxidectin and melarsomine protocols for canine heartworm treatment. Presented at: American College of Veterinary Internal Medicine Forum; June 19-21, 2025; Louisville, KY.
2. Keep the worms out of your pet’s heart! the facts about heartworm disease. FDA. December 22, 2022. Accessed August 13, 2025. https://www.fda.gov/animal-veterinary/animal-health-literacy/keep-worms-out-your-pets-heart-facts-about-heartworm-disease