Vet holding vial and syringe

Keeping your pet free of heartworms has always been important, but the need for prevention is back in the spotlight because supplies of Immiticide, the drug used to treat heartworm infestation in dogs, have run out.

In a letter earlier this month, Merial, the manufacturer of Immiticide, asked veterinarians to help conserve existing supplies. The announcement led to some “stocking up,” and now the company has no product to sell. The shortage was caused by difficulties in sourcing one of the key ingredients and the company is not sure when additional doses of the drug will be available.

The Situation

“We have nothing to fall back on,” said Dr. Wallace Graham of the American Heartworm Society, whose practice in Corpus Christi, Texas, is in a part of the country where heartworm disease is endemic. “I personally have enough Immiticide here to finish the five dogs I’m currently treating. But when that’s gone, it’s gone.”

The organization, which exists to educate pet owners about heartworm disease, prevention, and treatment, advises that heartworms are found in all parts of the continental United States as well as Hawaii. Pets suffering from adult heartworms can experience permanent organ damage or even die as the medication kills the worms. Although the treatment, when properly administered, has a good safety record, prevention has long been considered the safest option for pets

“For those dogs who test positive for heartworms now, we can manage heartworm disease, but that’s all,” Graham said. “The most critical part in this animals is curtailing exercise — and that can be very hard for some active dogs.”

Graham said that exercise can trigger a coronary crisis in dogs with adult heartworms, because vigorous activity could dislodge foot-long parasites, forming a lethal blockage in the cardiovascular system.

Guarding Against Heartworms

“We veterinarians have long known that prevention is far less risky than treatment when it comes to heartworms," said Vetstreet’s Dr. Marty Becker, a practicing veterinarian in north Idaho who is also a regular on Good Morning America and The Dr. Oz Show. “This situation should bring that point home even more strongly.”

Heartworm preventive medications kill immature worms before they can settle in the heart and grow. Giving or applying medication once a month has long been a basic tenant of responsible pet care. There is also an injection that can be given every six-months. But strays and dogs in poorer areas are unlikely to be as well cared for, which puts them at high risk for heartworm infestations.

If you are concerned that you may not have been as vigilant as you should have been about heartworm prevention, talk with your vet. He may give your pet a blood test to check for heartworms. To learn about protecting your pet, read our article on heartworm prevention and be sure to talk with your veterinarian about what is best for your animals.