Heartgard vs. Interceptor vs. Sentinel

When it comes to protecting your furry friend from heartworms and other parasitic infections, choosing the right medication is crucial. Heartgard, Interceptor, and Sentinel are three popular options, each with its own set of benefits and considerations.

Understanding the Basics

Before we compare the three, let’s understand what heartworm is and why prevention is essential. Heartworm disease is a severe and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and occasionally in the right side of the heart. It is transmitted through mosquito bites and is prevalent in many parts of the United States.

Prevention is vital as treatment for heartworm disease can be expensive and complicated, with no guarantee of success. Now, let’s dive into the specifics of each medication.


Heartgard is one of the most popular heartworm preventatives on the market.

  • Active Ingredient: Ivermectin
  • Parasites Targeted: Heartgard protects against heartworms, and also treats and controls roundworms and hookworms.
  • Form: Chewable tablet
  • Frequency: Monthly

Key Takeaways:

  • Heartgard is a reliable option for heartworm prevention and also tackles other common parasites.
  • It does not protect against whipworms or fleas.


Interceptor is another well-established name in heartworm prevention.

  • Active Ingredient: Milbemycin Oxime
  • Parasites Targeted: It prevents heartworm disease and also treats and controls roundworms, hookworms, and whipworms.
  • Form: Chewable tablet
  • Frequency: Monthly

Key Takeaways:

  • Interceptor offers a broader spectrum of parasite control compared to Heartgard, including whipworms.
  • It does not cover flea prevention.


Sentinel is a more comprehensive option in parasite prevention.

  • Active Ingredients: Milbemycin Oxime and Lufenuron
  • Parasites Targeted: It prevents heartworms, and treats and controls roundworms, hookworms, whipworms, and also helps in the prevention of flea eggs from developing.
  • Form: Chewable tablet
  • Frequency: Monthly

Key Takeaways:

  • Sentinel offers a broad spectrum of parasite control plus a unique ingredient to tackle flea eggs.
  • It does not kill adult fleas.

Comparison Table

Features/Products Heartgard Interceptor Sentinel
Prevents Heartworms
Treats/Controls Roundworms
Treats/Controls Hookworms
Treats/Controls Whipworms
Handles Flea Eggs
Kills Adult Fleas
Form Chewable Chewable Chewable
Frequency Monthly Monthly Monthly

Making the Right Choice

Selecting the best heartworm prevention medication for your pet depends on your specific situation, your pet’s health, and the particular parasitic threats in your area. Here’s what to consider:

  • Health and Age of Your Pet: Ensure the medication is suitable for your pet’s age and health status.
  • Geographical Location: Some areas have higher risks of certain parasites.
  • Your Pet’s Lifestyle: Outdoor pets might have different needs compared to indoor pets.


In summary, Heartgard is a solid choice for heartworm and basic parasite prevention, Interceptor adds whipworm protection to the mix, and Sentinel provides a comprehensive package including a component for flea control.

Frequently Asked Questions

What Are the Possible Side Effects of These Medications?

Heartgard: Heartgard is generally well-tolerated by most dogs. However, some pets might experience digestive upset, including vomiting or diarrhea. Rarely, neurological side effects like lethargy, incoordination, and seizures can occur, especially in breeds sensitive to ivermectin.

Interceptor: Interceptor is also considered safe for most dogs. Potential side effects are rare but may include vomiting, diarrhea, and lethargy. Dogs with a pre-existing health condition or those sensitive to milbemycin oxime might be at a higher risk for adverse reactions.

Sentinel: Sentinel shares similar side effects to Interceptor due to the common active ingredient, milbemycin oxime. Additionally, as it includes lufenuron for flea prevention, some dogs might experience mild skin reactions or temporary hair loss at the application site.

Can I Switch Between These Medications Easily?

Switching between heartworm preventatives should always be done under the guidance of a veterinarian. It’s crucial to ensure continuous protection, as a lapse might leave your pet vulnerable to heartworm infection. Your vet will guide you on the appropriate transitioning process, which might include a heartworm test before switching.

What Should I Do If I Miss a Dose?

If you miss a dose of any heartworm preventative, give the missed dose as soon as you remember. However, if it’s close to the time for the next dose, skip the missed dose and continue with the regular schedule. Never double up on doses without consulting your veterinarian. If you’ve missed more than two months of prevention, contact your vet as your pet might need to be tested for heartworm before resuming medication.

Are These Medications Safe for All Breeds?

While these medications are safe for most dog breeds, some breeds are sensitive to the active ingredients in these products. Breeds like Collies, Shetland Sheepdogs, and Australian Shepherds can have a genetic mutation that makes them more susceptible to the toxic effects of ivermectin (found in Heartgard) and milbemycin oxime (found in Interceptor and Sentinel). Always consult your vet to ensure the chosen preventative is safe for your dog’s breed and health status.

Do These Medications Protect Against Ticks?

None of Heartgard, Interceptor, or Sentinel provide protection against ticks. If ticks are a concern in your area or for your pet’s lifestyle, you might need to consider an additional tick preventative medication or choose a product that offers both heartworm and tick protection.

How Do I Choose the Best Option for My Pet?

The best option depends on various factors including your pet’s health, the prevalence of certain parasites in your area, and your preference in managing different types of parasites. Here’s a quick guide:

  • Choose Heartgard if you’re looking for a straightforward heartworm and basic parasite prevention.
  • Opt for Interceptor if you need additional protection against whipworms.
  • Select Sentinel if you want comprehensive parasite control along with flea egg prevention.

Regardless of your choice, the most important factor is consistency in administration and regular veterinary check-ups to ensure the ongoing health and protection of your pet.

Is There a Need for Year-Round Prevention?

Yes, veterinarians widely recommend year-round heartworm prevention. Heartworms are transmitted through mosquito bites, and it can be challenging to predict mosquito activity accurately. Additionally, regular administration helps in establishing a routine, minimizing the risk of missed doses.

How Does Sentinel Prevent Fleas Without Killing Adult Fleas?

Sentinel contains lufenuron, an insect development inhibitor, which prevents flea eggs from hatching and larvae from developing. While it’s effective in breaking the flea lifecycle, it doesn’t kill adult fleas. If your pet has a current flea infestation or if adult fleas are a significant concern, additional flea control measures might be necessary.

Can Pregnant or Nursing Dogs Take These Medications?

Heartgard: Heartgard is deemed safe for use in pregnant or nursing dogs. However, as with any medication given during pregnancy or lactation, it’s paramount to consult with your veterinarian before administration to ensure it’s the right choice for your pet’s unique situation.

Interceptor: Interceptor also falls into the category of medications considered safe for pregnant and nursing dogs. Still, veterinary guidance is crucial to balance the benefits and potential risks, ensuring optimal health for both the mother and her offspring.

Sentinel: The use of Sentinel in pregnant, breeding, or nursing dogs has not been evaluated conclusively. It’s imperative to discuss with your veterinarian whether the benefits of using Sentinel during these critical life stages outweigh any potential risks.

How Do These Medications Interact With Other Drugs?

Heartgard: Heartgard has a low incidence of drug interactions. However, caution should be taken if your pet is on any other medications that affect the nervous system.

Interceptor: Interceptor may interact with certain drugs, including high doses of ivermectin and other drugs that depress the central nervous system. Always inform your veterinarian of all medications and supplements your pet is taking before starting Interceptor.

Sentinel: Due to its additional ingredient for flea prevention, Sentinel may have more potential interactions than Heartgard or Interceptor. Discuss all current medications with your veterinarian to ensure safe use.

What Happens if My Dog Ingests More Than the Recommended Dose?

Heartgard: While Heartgard is generally safe, an overdose can lead to side effects such as vomiting, diarrhea, and, in severe cases, neurological issues. Immediate veterinary attention is recommended if an overdose is suspected.

Interceptor: Similarly, an overdose of Interceptor can lead to vomiting, diarrhea, depression, and in severe cases, seizures. Contact your veterinarian or an emergency animal poison control hotline if an overdose occurs.

Sentinel: An overdose of Sentinel can result in similar symptoms to an Interceptor overdose, with the added risk due to the lufenuron component. Seek veterinary care immediately if you suspect your pet has ingested too much of the medication.

How Do I Know if My Dog Has Heartworms, and How Are They Treated?

The symptoms of heartworm disease can be subtle and may not appear until the disease has progressed. They can include a persistent cough, lethargy, decreased appetite, and weight loss. Heartworm disease is diagnosed through a blood test.

Treatment for heartworm disease can be expensive and complicated, requiring multiple visits to the veterinarian, blood tests, x-rays, hospitalization, and a series of injections. The best approach is always prevention.

What Should I Do if I Switch Vets?

If you switch veterinarians, ensure all your pet’s medical records, including their heartworm prevention history, are transferred to the new clinic. This ensures continuity in care and helps your new vet make informed decisions regarding your pet’s health.

Can I Buy These Medications Without a Prescription?

Heartgard, Interceptor, and Sentinel are all prescription medications. A veterinarian must approve their use for your pet, ensuring they are safe and appropriate for your dog’s specific needs and health status.

Are There Any Natural Alternatives to These Medications?

While there are natural and holistic approaches to parasite prevention, their effectiveness is often debated and not scientifically proven. Before considering any natural alternatives, have a thorough discussion with your veterinarian about the potential risks and benefits, ensuring you are not putting your pet at risk of parasite infestations.

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