Why I Give My Dog Heartworm Preventative Medication Every Single Month

Most of these medications also protect dogs -- and people -- from other potentially serious diseases.


The first day of the month just passed. This month, like every month, I had a number of items on my first-of-the-month to-do list. Several bills were due on the first, and since I don’t want to be turned out of my home and onto the streets, I paid them. Almost as important, for me, was a monthly chore involving my pal Buster.

On the first of every month, Buster receives his flea and heartworm preventatives. Fortunately, the heartworm preventative is easy to give — I use Heartgard Plus, which comes in a palatable flavored tablet. Buster loves it.

I know plenty of people who don’t administer heartworm prevention to their pets. I have heard many reasons. Some folks cite the expense of the medications. Others are philosophically opposed to medicating their pets monthly. Some people don’t think heartworm is a problem in their area. And some simply can’t remember to give the medications regularly.

That last excuse is why Buster gets his Heartgard Plus on the first — it’s an easy day to remember. And although I understand the logic behind the other arguments, I will say that I don’t agree with them. I think the administration of monthly broad spectrum (I’ll come back to what that means in a moment) heartworm preventatives is a very good idea indeed.

I live in San Francisco, California. Heartworm is rare here. It is true that many dogs live here and don’t contract heartworm disease even if they don’t receive regular heartworm prevention. That cannot be said about plenty of other places. In many parts of the world — anywhere tropical, and anywhere where it’s ever warm and humid — heartworm is endemic. Dogs who don’t receive heartworm prevention are virtually assured of being infested with the parasites. (For instance, remember that Kabang, the hero dog from the Philippines who lost her snout, had to undergo treatment for heartworm before she could undergo surgery for her snout.)

But although heartworm disease is rare here, it does exist. In fact, there are very few places on Earth where heartworm doesn’t exist. And make no mistake: Heartworm is a serious disease.

Heartworms, as their name implies, are blood parasites that live in the heart and the arteries leading out of the heart. They cause physical damage to the structures they infest, and infested dogs can suffer from heart failure, respiratory distress, and acute lung damage due to so-called embolic events when worms die.

Heartworms are spread by mosquitoes. And, given that mosquitoes can live indoors year round, the American Heartworm Society recommends year-round heartworm prevention for all dogs. However, the disease is most commonly spread during warmer months. We are in peak heartworm season right now.

The most common treatment for heartworm disease utilizes a series of injections of an arsenic-based product. Side effects and complications are common, and treatment is extremely expensive (many times more expensive than a lifetime supply of preventatives). To make matters worse, the product is available in limited quantities only, and your vet might not be able to get it if your dog contracts heartworm. There is no doubt that in the world of heartworm, prevention is better than cure.

I’m glad that Buster is protected against heartworm disease. But as bad as the disease is, I have a confession to make. The main reason I administer Heartgard Plus to Buster is not to protect him against heartworm disease. I like the product for one of its fringe benefits.

Heartgard Plus and similar products such as Trifexis are so-called broad spectrum anthelminthics. This means that they do not merely prevent heartworm disease. They also protect against some other types of worms. Crucially, they protect against roundworms.

Roundworms are extremely common. They infest dogs’ intestines, and they commonly cause diarrhea. Severe infestations can cause vomiting, emaciation, and other serious complications. Puppies in particular are susceptible and, due to a fascinating feature of the roundworm lifestyle, almost all puppies are infested at birth or shortly thereafter.

Buster is not a puppy, and roundworms probably wouldn’t sicken him too badly. I nonetheless remain quite adamant about keeping him free of them. Here is why: Roundworms aren’t merely a threat to dogs. The most common canine roundworm also can infest humans.

Children, especially toddlers, are most susceptible. The worms are spread through fecal-to-oral contamination. Young people often are lacking in their sense of hygiene. They also do not have fully developed immune systems, which can make them susceptible to aberrant forms of parasitosis.

In children infested with canine roundworms, there have been documented cases of visceral larval migrans, ocular larval migrans, and even cerebral larval migrans. In these scary-sounding (and, in fact, truly scary) conditions, roundworm larvae migrate through and wreak havoc upon the internal organs, eyes, and brains of affected individuals. It’s serious stuff.

Buster, like all dogs, poops. I pick it up, but I couldn’t live with myself if a roundworm egg were left behind and a child subsequently became ill. Canine roundworms are a significant public health menace. There is no way I’m going to let Buster be a public health threat.

I don’t have children, but I do have many young nieces and nephews. Many of them love to play with Buster. And, thanks to his monthly heartworm (and roundworm) preventative, I do not worry that they will come to any harm as a result.

Learn more about dogs with Dogster:

Got a question for Dr. Barchas? Ask our vet in the comments below and you might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)

1 thought on “Why I Give My Dog Heartworm Preventative Medication Every Single Month”

  1. My advice to you is to research heartgaurd. It is a pesticide. It’s killings dogs everyday. Trifexus is another brand that is fatal for dogs. My dog was 4 when he died last year.
    I came home and found him dead.
    After researching the Heartworm medication i was giving him once a month I discovered how dangerous it is.
    There are natural alternatives.

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