Interceptor for dogs is a broad spectrum heartworm medicine for dogs and an antiparasitic that exerts its action against a variety of mites and worms. It is approved by the FDA in the prevention of heartworm infections in dogs especially those brought about by Dirofilaria immitis as well as in the control and elimination of other nematode genera such as hookworms and whipworms. In simple words, Interceptor is a drug that is especially formulated for the prevention of heartworm infestations and the treatment of intestinal worms in dogs. It is also used, albeit off-label, as a miticide in the control of mange in dogs. It is recommended for use in dogs and puppies that are at least 4 week of age and weigh at least 2 pounds. One thing that is great about Interceptor for dogs is that it is considered safe for both lactating and pregnant dogs. It comes in a palatable tablet formulation for a once monthly dosing.

dogs laying down


Interceptor for dogs is indicated as a preventative for use on dogs as well as puppies that are at least 4 weeks old and weigh not less than 2 pounds. More specifically, it is intended for the prevention and control of the following.

  • Heartworm disease 

Caused by Dirofilaria immitis, heartworm disease is a serious and often fatal condition resulting from massive destruction of red blood cells and severe shock. The progression of the condition is quite slow, however, as Dirofilaria immitis has been known to be present in dogs for as long as 7 years. It typically starts with the bite from a mosquito that carries the filarial organism. It injects the larva into the bloodstream of dogs where it lodges in the pulmonary arteries. Here, inflammatory changes result in tissue damage of the arteries while continuing proliferation of the heartworm can impede the efficient flow of blood. This leads to poor oxygenation in the tissues distal to the site of the blockage.

The tissue damage produced by Dirofilaria immitis occurs at a much faster rate than the speed at which the dog’s body is able to repair it. Because of the continuing tissue damage to a particular area of the pulmonary artery, this creates a variety of microaneurysms and blood clots that further block the flow of blood. To compensate, blood will have to be rerouted to worm-free arteries. This also favors the leakage of plasma into the extracellular compartment which technically ‘floods’ the alveoli of the lungs resulting in pulmonary edema. This further reduces the lung’s ability to draw oxygen from the outside air.

The combination of arterial tissue damage, blood vessel blockage, and pulmonary edema all lead to an increase in the pressure in the vena cava and the right side of the heart. Over time, this leads to heart failure. At the same time, your dog’s immune system will go into hyperdrive in an effort to contain the situation. This releases extremely huge amounts of antibodies into the general circulation where they can attach to other body organs and initiate inflammatory changes. This results in further tissue damage that now extends to the joints, kidneys, and the eyes.

The fatal blow comes from complete blockage of blood flow through the heart, leading to what is called Vena Cava Syndrome. Within 2 days, often as short as 1, severe shock and massive RBC destruction will lead to death.

  • Hookworm disease 

Hookworm disease is another fatal parasitic infection caused by Ancylostoma tubaeforme and/or Ancylostoma caninum. These parasites are especially fatal to puppies. While these hookworms don’t invade the heart, they do exert their lethality among puppies by drawing blood from the small intestines of dogs. This initiates a variety of inflammatory reactions as well as the development of anemia which can significantly impair oxygen delivery to the tissues.

  • Intestinal ascariasis 

While not as deadly as heartworm or hookworm disease, intestinal ascariasis in dogs can still pose great concern especially among young puppies. The most common ascarids found in dogs include the Toxocara species canis and leonina. These are your classic parasites where they rob the dog of the nutrients that are intended for its tissues. This leads to various signs of canine malnutrition including an emaciated appearance, dull coats, and even pot-bellied appearance. If these parasites migrate to the lungs, they can cause severe pneumonia especially among puppies.

  • Whipworm disease 

If heartworms reside in arteries and the heart and hookworms and ascarids live in the small intestines, whipworms have a special affinity for the large intestines of dogs where they attach to the lining of the colon. This leads to severe irritation producing watery and often bloody diarrhea, general debilitation, and weight loss in dogs. Trichuris vulpis is the most common whipworm that is found in dogs.

  • Mange in dogs 

While Interceptor for dogs does not list control of mites as one of its indications, studies show that its active ingredient, Milbemycin oxime is actually effective against certain species of mites, especially those that produce mange in dogs. Mange is an inflammatory skin disease that is characterized by intense itching and a variety of inflammatory changes in the skin. These are often caused by either Demodex canis, which produces demodetic mange, or Sarcoptes scabiei canis, which is the causative agent of sarcoptic mange.

Benefits of Interceptor

The following are the known benefits of using Interceptor on dogs.

  • Protects dogs against heartworms and intestinal parasites 

Interceptor is a heartworm medicine for dogs. It helps prevent the growth and development of Dilofilaria immitis larva so that it will not have a chance to produce the various effects it has on the body, especially the heart and the arteries. It is also effective against intestinal hookworms, ascarids, and whipworms to provide a host of benefits including improved tissue oxygenation, better absorption of nutrients, and enhanced elimination of wastes.

  • Aids in the control of demodetic and sarcoptic mange 

The off-label use of Interceptor against mange in dogs can bring relief to your pet suffering from this type of skin disease. It simply means it doesn’t have to suffer from intense itching, swelling, and pain anymore. This can help provide better comfort for your pooch so that it will be able to function normally.

  • Facilitates easier administration 

Interceptor comes as a chewable tablet form which aids in its easier and more convenient administration. You will also feel more confident about your dog receiving the full spectrum of preventative benefits of the antihelminthic and miticide preparation. It is also administered once a month so there’s no need to constantly remind yourself about the need for a more frequent administration. Simply mark on your calendar the next dose and you’re done.

  • Promotes optimum growth and development in puppies 

These parasitic diseases mostly affect puppies that are still discovering a lot about their world and about themselves. By giving them the protection they need against these diseases they are able to grow and develop to their optimum. This means you get to enjoy their company for many years to come without having to worry about any untoward incident that may spring from not protecting them against these diseases in their puppyhood.

How Interceptor Works

Interceptor heartworm medicine for dogs contains the active ingredient Milbemycin oxime. This is a chemical that belongs to a class of broad spectrum antiparasitic agents known as Milbemycins which, in turn, are similar in action to another group of antiparasitic agents called Avermectins. The only difference between Milbemycins and AVermectins is that Milbemycins have a longer plasma half-life. This means that its therapeutic effects last longer than those afforded by Avermectins.

Milbemycin oxime effectively prevents the transmission of electrical signals across the various neurons and muscle cells of susceptible parasites. It does this by enhancing the activity of glutamate on the chloride channels on the nerve and muscle cell surfaces. This effectively opens the gates of these channels so that chloride ions from the outside of the cell will rush in towards the inside of the cell. This leads to hyperpolarization of the cell membrane which, in turn, cause paralysis or the cessation of neuromuscular activity.

Because electrical signals are no longer transmitted from the central nervous system of the parasite to its muscles and neurons of the peripheral nervous system, the parasite eventually dies.

Potential Side Effects

The antihelminthic and miticide is generally well tolerated. However, it is not uncommon to see some minor side effects such as glassy eyes, vomiting, depression, weakness diarrhea, loss of appetite, and the increased production of phlegm.

In rare cases, dogs may develop adverse reactions that can be considered as serious or life threatening. These typically include:

  • Nervous system damage
  • Seizures
  • Extremely low blood pressure or shock
  • Coma
  • Respiratory failure

Things You Should Know about Interceptor

Interceptor is a heartworm medicine for dogs and cats that is FDA-approved and is available only with your vet’s prescription. It is presented as a chewable tablet in artificial beef flavor. It comes in 4 different color variants, each containing a different dose of Milbemycin oxime to account for the weight differences in dogs.

  • Brown –contains 2.3 milligrams of Milbemycin oxime and is given to dogs weighing 2 to 10 pounds
  • Green – contains 5.75 milligrams of Milbemycin oxime and is given to dogs weighing 11 to 25 pounds
  • Yellow – contains 11.5 milligrams of Milbemycin oxime and is given to dogs weighing 26 to 50 pounds
  • White – contains 23 milligrams of Milbemycin oxime and is given to dogs weighing 51 to 100 pounds

It is given once a month for the prevention of heartworm disease and the control of susceptible intestinal parasitism.

What You Should Tell Your Vet before He Prescribes Interceptor

Your vet must know if your dog is allergic to Milbemycin oxime. He also needs to know if your dog is receiving any other form of canine medication or supplement as these may interact with Milbemycin oxime.

sick dog

How to Give Interceptor to Your Dog

Administering Interceptor to your dog is relatively easy. Simply take the weight measurement of your pooch as accurately as you possibly can then use the appropriate Interceptor color that corresponds to your pet’s weight. If your pet’s weight happens to be more than 100 pounds, you only have to provide a combination of the flavored chewable tablets. For example, if you have a dog that weighs 120 pounds, you need to give it one tablet each from Interceptor White and Interceptor Green or any other combination that will cover the 120 pounds.

Interceptor for dogs should be given on the same exact date of each month. For example, if you gave the initial dose on the 3rd day of the month, then you have to make sure to give it every 3rd day of the succeeding months. This drug can be given all year round. If you want to use it seasonally, you need to give the first dose within 30 days of your dog’s initial exposure to mosquitoes.  You also need to give the last dose of seasonal Interceptor within 30 days of your canine friend’s last mosquito exposure.

When administering Interceptor to dogs, it is important to supervise them to help make sure they will swallow the entire drug. The good thing is that most dogs love the taste. Additionally, you can crush it and mix it with your dog’s food.

What to Do If You Miss a Dose

As always, make sure to give the missed dose immediately upon remembering. Do not tempt fate by giving twice the dose.

What to Do in Case of Interceptor Overdose

If any of the adverse reactions we described above are observed in your dog, the services of a veterinarian are an absolute must.

Some Drug Interactions

Caution should always be exercised when giving Interceptor to dogs that are also receiving amiodarone, cyclosporine, diltiazem, azoles, carvedilol, spironolactone, erythromycin, verapamil, clarithromycin, and tamoxifen. If your pooch is already on a heartworm medication, you should not give Interceptor at all.

Interceptor for dogs is an effective way to protect our puppies and dogs against heartworm disease. It is also effective in controlling active intestinal parasitism produced by roundworms, hookworms, and whipworms. It is generally safe and very easy to administer because of its convenient once-monthly dosing and useful color-coded formulations.

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  1. Interceptor – PetMD


Olivia Williams
Olivia is our head of content for, mum of one and a true animal lover. With 12 different types of animal in her family, it's never a dull moment. When she isn't walking the dogs, feeding the cats or playing with her pet Parrot Charlie, you will find her product researching and keeping the site freshly updated with the latest products for your pets!


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