Do Senior Dogs Need Heartworm Medication? [Complete Guide]

As our beloved canine companions age, their needs and vulnerabilities change, demanding extra attention to their health and well-being. One often-overlooked aspect of senior dog care is the necessity for heartworm medication.

While we cherish the golden years of our furry friends, their advanced age makes them more susceptible to various health issues, including the insidious threat of heartworm disease.

This comprehensive guide aims to shed light on the critical question: Do senior dogs need heartworm medication? Heartworm disease, caused by parasitic worms transmitted through mosquito bites, can be devastating, especially for older dogs with compromised immune systems.

In this guide, we will explore the importance of heartworm prevention for senior dogs, the types of preventive medications available, and the steps you should take to safeguard your aging companion’s health.

Can Older Dogs Get Heartworms?

The question on every dog owner’s mind: Do senior dogs need heartworm medication?

Any dog, no matter their age, can contract heartworm disease.

Dogs are natural hosts for these parasites, meaning that they offer a biological shelter that nourishes the parasite as it grows. However, the only way that dogs can receive heartworms is if they are bitten by a mosquito infected with the heartworm parasite.

Do senior dogs need heartworm medication if they are at risk of becoming infected? The answer is a definite “yes”.

What Is Heartworm Disease?

Heartworm disease is caused by the parasitic roundworm Dirofilaria immitis. It spreads through bites from mosquitoes who are already infected with the parasite.

Dogs, cats, and ferrets are most at risk for contracting this disease, with dogs being most commonly affected. According to the American Heartworm Society, over a million dogs within the United States suffer from heartworm disease.

The life cycle of heartworms is simple but can have deadly consequences.

Heartworm larvae begin to develop in a mosquito’s body after it bites an infected animal. When the newly infected mosquito bites another animal, the larvae transfer to the animal’s bloodstream.

Here, the larvae travel to different parts of the animal’s body, where they mature and reproduce over time. It takes approximately six to seven months before heartworms reach full maturity and become spaghetti-like strands that can grow between 4 to 12 inches long.

In dogs, heartworms have a general lifespan of five to seven years. These adult heartworms can cause severe and sometimes permanent damage to the body after they are fully developed, clogging up the heart and lungs, among other organs.

Adult worms are capable of causing long-term health problems, such as lung disease and heart failure. In some extreme cases, heartworm infestation can even result in death.

Testing for Heartworms

Young female veterinarian examining dog.

Heartworm disease is both dangerous and progressive, and early detection is critical to your pet’s overall health.

This disease can often go undetected for long periods, as symptoms usually take a while to become noticeable. Testing is the only way to ensure your dog is healthy and heartworm-free.

When to Test?

However, figuring out when to test can be tricky.

It takes up to seven months for heartworms to be mature enough to be diagnosed and approximately six months for dogs to test positive post-infection. Be sure to talk with your vet about the best times to test your dog for heartworms.

Dog owners should make sure their dog receives a heartworm test every year at their annual check-up. Both young and adult dogs should receive an examination every six months the first year after their initial visit and every 12 months after that.

All dogs under seven months can begin a heartworm prevention routine without being tested for heartworms.

However, dogs who are at least seven months of age should be tested for heartworms before taking any sort of heartworm prevention medication. This fact is important to note, as preventives will not kill the pre-existing heartworms.

How is the Test Conducted?

When conducting a heartworm infection test, your dog’s vet will take a small blood sample and examine it for heartworm proteins that are referred to as antigens. After mating, the adult female heartworms release these antigens into the animal’s bloodstream.

It takes around five months after the mosquito bite for these antigens to be discoverable. The vet may also perform a particular test to look for microfilariae (infant larvae) circulating in the blood, which can take about six months to be detected.

Even if your dog is already on a heartworm preventative medication, it’s still essential to visit the vet for an annual heartworm infection test. Also, keep in mind that late or missed doses of preventive medicine can leave your dog vulnerable to heartworm disease.

Regular testing is always the most accurate way to ensure that your dog is healthy. Early discovery of heartworm infection can lower your dog’s risk of complications and help their health remain intact.

Symptoms of Heartworms in Dogs

Sick-looking brindle puppy

Unfortunately, a majority of dogs show little to no symptoms in the initial stages of heartworm disease. It often takes months before a dog shows any warning signs. More symptoms tend to surface as the condition worsens.

The severity and prevalence of symptoms depend on how advanced the disease is within the dog’s body.

Your dog’s condition corresponds with their “worm burden”, or the number of heartworms inside them. More worms equate to more symptoms and increased severity of symptoms.

Even if your dog appears healthy, there could still be heartworms growing inside them.

Common early symptoms can include a mild, occasional cough and noticeable fatigue after moderate physical activity. It’s easier to notice symptoms occurring in more active dogs, as heartworms can impact their breathing and make playtime much more difficult.

More severe symptoms can consist of the following:

  • A continual dry cough
  • Sickly appearance
  • Weight loss or loss of appetite
  • Bloated belly
  • Shallow breathing
  • Distended chest
  • Fainting episodes
  • Abnormal breathing
  • Pale gums
  • Bloody or dark urine
  • Exhaustion after mild exercise

What’s the Risk of My Dog Contracting Heartworm Disease?

Mosquito swarm dusk

The risk of your dog contracting heartworm disease depends on a variety of factors such as where you live, the weather conditions or season, and the types of wildlife in your area. Heartworm disease is not contagious, so animals cannot pass it to each other; it can only be transmitted through mosquito bites.

Your dog’s risk increases if you live in a more humid region where there are many mosquitoes. The risk of heartworm transmission also increases if you travel or live in areas where heartworm infection is more common.

It can also be contracted if you fail to administer the proper preventive heartworm medication to your dog regularly, or live in an area where there are frequent sightings of coyotes, wolves, and foxes who are common carriers.

In 2019, the American Heartworm Society released survey results indicating the states with the highest heartworm disease incidence. These high-risk states included:

  • Louisiana
  • Mississippi
  • South Carolina
  • Arkansas
  • Alabama

Nonetheless, heartworm disease continues to impact dogs within all 50 states.

Treatment for Dogs With Heartworm Disease

Hand feeding dog heartworm pills

Do senior dogs need heartworm medication? Heartworm disease can kill animals, including senior dogs, if left untreated. Fortunately, effective FDA-approved treatment options are available to you if your dog is diagnosed with heartworm disease.

Make sure to always discuss your dog’s particular medical situation with your vet to determine the proper course of action. They can determine the best timing, type, and frequency of your dog’s treatment.

Successful treatment requires multiple vet trips and lots of time, patience, and discipline. But with the help of their trusted vet, dedicated dog owners can lead their pups back to full health. The following are commonly used methods by vets.

Drug Injections

Dogs diagnosed with heartworms often undergo a series of drug injections that usually span a period of six months, depending on the vet’s specific treatment protocol. Melarsomine is often the medication that is prescribed and injected to kill off the adult heartworms.

Oral Medications

An infected dog can experience an inflammatory reaction as the heartworms begin to die off after a heartworm drug injection.

For this reason, vets often prescribe oral doses of prednisone or doxycycline as a form of pre-treatment. Both drugs can prevent this harmful bodily response and accompanying complications.

Continued Heartworm Preventive Medication

Heartgard Plus packet

A series of heartworm preventative medication can also be used throughout treatment, as this will help wipe out any heartworms that are still developing in the dog’s body. Some of the most frequently used options include ivermectin, milbemycin oxime, moxidectin, and selamectin.

However, as always, it is essential to discuss proper treatment methods with your vet. Giving a preventive to a heartworm-positive dog can have negative consequences if not administered in the correct dose and at the right time.

As bad as it might sound to accidentally give your dog a double helping of heartworm medication, it’s actually much, much worse to miss or delay a dose!

Restricted Exercise

You should restrict your dog from exercise as much as possible from the point of diagnosis until treatment is finished. As heartworms die, they split off into pieces in the bloodstream and can cause blockages.

When your dog exercises, blood flow increases throughout their body. When blood cannot flow freely, it can lead to a life-threatening embolism (a condition in which a blood clot blocks an artery).

Alternative Options

Heartworm treatment can be expensive, and sometimes dog owners do not have adequate funds to pay for it.

Although most vets recommend standard treatment methods, there are a few alternatives available as well. A recent study has shown that combining Advantage Multi, Bayer, and doxycycline could be a successful treatment plan for early infection stages.

These non-conventional methods are usually referred to as “slow kill” protocols, as they often take longer to work.

However, the American Heartworm Society does not recommend these slow kill protocols, as they are less effective, unpredictable, and can damage the body over a prolonged period.

Surgical Intervention

Surgery is only recommended in extreme, life-threatening cases when the heavy worm burden blocks blood flow to the heart. This condition is also referred to as caval syndrome. At this point, the heartworms must be extracted from the body as soon as possible to prevent death.

Best Heartworm Prevention for Senior Dogs

Dog turning away from Heartgard packet

You may still be wondering: Do senior dogs need heartworm prevention?

Yes. All dogs are at risk of heartworm disease and need year-round protection.

Dog owners should ensure that they are taking the necessary steps to keep their dogs safe from heartworms, no matter their age. Most heartworm preventives are relatively inexpensive, simple to administer, and safe for dogs.

It is strongly recommended to give your dog heartworm medication every month of each year and have them tested at least once a year at their routine check-up.

The best prevention is giving your dog regular doses of appropriate, vet-approved preventive medication and ensuring they receive the appropriate routine tests as suggested by your vet.

Types of Heartworm Preventive Medications

Preventive medications are prescribed by your dog’s vet and come in a variety of forms that should be given to your dog monthly.

Depending on your dog’s specific situation and behavior, you may want to use a chewable or non-chewable pill, a topical product, or an injection. Some medications are multi-use and offer protection against fleas and other types of parasites like whipworms and tapeworms.

Oral Medicines

A simple way to prevent heartworms is to give your dog oral preventive medication each month through chewable or non-chewable tablets.

Commonly used oral medicines include Heartgard Plus and Sentinel. These pills are intentionally flavored for your dog to enjoy, so it’s essential to keep them in a safe place to prevent your dog from overdosing.

Topical Products

These medications are applied directly to your dog’s skin each month (usually on the back of their neck) and are absorbed into the skin.

Advantage Multi for Dogs is a popular, topical product that helps kill microfilariae and also serves as a safeguard from mites, hookworms, whipworms, and roundworms.

Be cautious when applying these types of products, as they can be dangerous to people or animals who contact them.


Heartworm shots are a viable option for dog owners who would rather not worry about monthly preventive medicine.

Instead, these injections are administered twice per year, helping eliminate the risk of forgetting a dose and leaving your pup unprotected. ProHeart 6 is a common, FDA-approved injectable preventive medication that must be administered by a vet every six months.

Mosquito Repellant

Mosquito repellant is not 100% effective and should not be used as the sole preventive measure for heartworms. However, it can still be a useful tool to prevent your dog from being bitten by mosquitoes.

Trust Your Vet with Heartworm Disease Prevention and Treatment

Gogi the corgi sitting in garden with flowers in the background

When it comes to heartworm prevention, testing, diagnosis, and treatment, trust your vet.

If your dog is positive for heartworms, your vet will work to provide the safest and most effective treatment option possible.

If your dog is negative for heartworms, your vet will prescribe the appropriate type and dosage of preventive medicine. Remember that prevention is key.

Overall, the best thing you can do as a dog owner is to discuss your dog’s specific condition with your vet and, together, determine the appropriate steps to take for prevention and treatment.

Doing so will help minimize potential complications and ensure that your senior dog’s health and wellbeing is in expert hands.

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