What You Should Know Before Switching Your Dog to an Annual Heartworm Shot

Heartworm disease is a potentially deadly condition that requires extensive treatment — think multiple medications and at least two months of complete rest — which is why veterinarians and dog owners work so hard to prevent it. The most common preventative treatment is an oral or topical medication given once a month, but recently, vets in the U.S. have started offering anti-heartworm shots that last for six or 12 months.

The biggest difference between heartworm shots and other heartworm medications is the type of anti-parasitic medication they use. ProHeart injections use moxidectin, and come in either six- or 12-month formulations; many topical medications (Advantage Multi and Advocate) also use moxidectin. HeartGard, a popular chewable tablet, uses either ivermectin or a combination of ivermectin and pyrantel. All of these medications are FDA-approved and effective, so the choice comes down to which format works better for you and your dog. Here are the pros and cons of switching to a shot.

The good: Convenience and price

A once- or twice-yearly heartworm shot can be more convenient than monthly doses. As long as they’re not getting vaccine boosters at the same appointment, your dog can can get the shot as part of a checkup — and you don’t have to worry about it until the next one. (Your vet may decide it’s safe to administer future heartworm shots and boosters at the same time, but until they know how your dog reacts, it’s best to spread them out.)

As you might expect, the cost of heartworm shots depends on how big your dog is and what your vet’s office charges for them. (Larger doses for big dogs cost more than smaller doses for little dogs, plus visit fees and labour costs.) But while shots are more expensive than oral and topical medications up front, the cost of the meds themselves work out to roughly the same price per year.

The bad: You can’t do them at home, and there’s no protection against other worms

Heartworm shots must be administered by a qualified veterinarian or technician, so you can’t do them on your own. If you’re already paying for a checkup, this is no big deal; if you need to schedule one just for the shot, it can wind up being more expensive than necessary.

The final downside to shots is potentially the biggest: Unlike some other anti-parasitic medications, moxidectin only protects against heartworm. While heartworm disease is more dangerous than other types of parasitic infections, it’s not the only one. Hookworms can cause severe anemia; tapeworms can cause weight loss and diarrhoea; roundworms can stunt a dog’s growth, making them especially dangerous for puppies. Depending on your dog’s risk factors for non-heartworm infections, your vet may recommend a combination drug that protects against more than one parasite.

There’s no universally right or wrong choice here. Heartworm shots are an ideal solution for lots of dogs, but not all of them. If you’re considering switching medications, talk to your vet first — they’ll give you the personalised advice you need to make your decision.