Interceptor vs. Sentinel: 2024 Comparison and Key Differences

Interceptor and Sentinel are parasitic treatments for dogs and cats. Veterinarians recommend these two treatments for issues like heartworms, fleas, and other types of worms. Since cats rarely get heartworms, these treatments are usually given to dogs. Cats are not immune to heartworms, but their physiology reduces the chances of being infected by them.

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Heartworm disease is blood-borne and can be fatal. The worms lodge themselves in the heart, pulmonary artery, and nearby blood vessels. Sometimes, they make their way into other areas of the circulatory system. Infected dogs can have up to 300 worms, with female worms measuring between 6 and 14 inches. Male worms measure between 3 and 7 inches in length.

Heartworms can stay in a dog’s body for up to five years. Female worms have millions of microfilaria, which live in the bloodstream. Dogs are infected during mosquito season, when mosquitoes bite dogs. The disease cannot be transmitted between dogs, only through mosquitoes.

Since most communities in the United States have mosquito problems for some or all of the year, dogs need heartworm treatments. Dog owners need to pay attention to the heartworm treatments they choose. Older treatment options had arsenic and other toxins, so dogs had severe side effects. New treatments are safer and are free of toxins.

By the time a veterinarian diagnoses a dog with heartworm, the fur baby could have an advanced form of the disease. In these cases, the worms often do severe damage to internal organs. Usually, dogs do not live long after a heartworm diagnosis. To keep dogs healthy, pet owners should give their fur babies regular heartworm treatments.

What to look for in a good pet treatment

Pets need to have parasite treatments for fleas, heartworms, and other worms. It doesn’t matter if your pet stays indoors all day or ventures outside, parasites can infiltrate your pet. To protect your pet from the damage that parasites do, you must give your fur babies preventative medication.

When you look for the perfect treatment, consider where your pet spends its time. Indoor pets might not need treatments that cover fleas as much as other parasites. Your pet’s age, weight, breed, and size affect the type of treatment that will work best. You should also consider your budget because some medications can have serious sticker shock.

Your pet’s demeanor should also be a consideration for the treatment you choose. Medications can be administered in several ways, from injections to pills, collars to creams. If your pet refuses to take oral medication, your options are limited. If your pet chews on collars, then you have to choose something else.

You should also consider how often you have to give your pet the treatment. Shots can be quick choices that last a long time, but some pills have to be given monthly or more frequently. Since most heartworm drugs work by paralyzing the parasite’s nervous system, it is essential to give the medication as directed.

Good flea and heartworm treatments should have limited side effects. No one wants to clean up pet vomit or diarrhea, and you certainly do not want your pet to suffer after having a treatment. But, a quick bout of diarrhea is a better option than having heartworms destroy your fur baby’s organs.

Interceptor and Sentinel Similarities

Interceptor and Sentinel are broad-spectrum parasite treatment options that are usually given to dogs. The two treatments prevent heartworm, roundworm, and hookworms.

Both medications are given monthly, and veterinarians recommend and prescribe both of them. Each has different dosages for dogs of various sizes. The medicines have two active ingredients. But they both use milbemycin oxime, which is a broad-spectrum antiparasitic to prevent worms and mites from making their homes in animals.

The medication prevents internal parasites, which are different from external parasites, like fleas and ticks. Both medications have similar side effects, like vomiting and diarrhea. They also can cause dogs to develop skin congestion, convulsions, and anorexia. Some dogs become lethargic and depressed, too.

Both Interceptor and Sentinel are available as chewable tablets. Some dogs chew them up and give no problems to their owners, but other dogs put up a fuss. Many dog owners will hide the tablets in dog food, so they know their dogs take the medication. Both medications are safe for dogs as young as one month of age.

Since dogs take this medication orally, pet owners need to be sure their dogs ingest the whole pill. Watch your fur baby because vomiting after taking the tablet could affect the efficacy. Stay in contact with your veterinarian if your dog vomits when taking either medication. Both are taking monthly, and they begin to work within hours of administering them.

Interceptor and Sentinel Differences

While Interceptor and Sentinel both kill heartworms, their impact on fleas and other parasites varies. Interceptor also kills hookworms and whipworms, while Sentinel does not. Sentinel kills fleas, but Interceptor does not. Sentinel is not effective against preventing dogs from developing tapeworms.

Interceptor tastes like chicken, while Spectrum tastes like bacon and beef. They are both soft and chewy so dogs can easily eat them.

The two medications have one ingredient in common, but the second one varies. Interceptor includes praziquantel, which helps milbemycin oxime kill worms and stop them from procreating. The World Health Organization recommends praziquantel to fight parasitic worm infestations. Both animals and pets can take this medication.

Sentinel includes an ingredient called lufenuron, which kills adult fleas and prevents them from reproducing. Sentinel is designed to fight fleas. It works by preventing flea eggs from hatching but does not kill adult fleas like other flea treatments.

As cats rarely develop heartworm, veterinarians do not recommend giving Interceptor to them. Veterinarians do recommend Sentinel for cats, but only after they weigh at least 1.5 pounds and are six weeks old.

Interceptor and Sentinel Pricing Comparison

Interceptor is available in four different dosage sizes. One of them is just for dogs, and the other three are for dogs and cats. The doses are designed to fit the weight of the fur baby. Each box of Interceptor includes six dosages, with one treatment lasting one month. A veterinarian has to prescribe the medication.

Sentinel is also available in four sizes. All four sizes are designed for dogs of different weights. Each box has six doses, and you give your dog one dose each month. Veterinarians must prescribe Sentinel.

Since the two medications come with similar sized dosages, it is easy to figure out which has a less expensive price per dose. Interceptor costs between $6 and $10 per dose, while Sentinel costs between $8 and $13 per dose. Interceptor is more economically priced, but Interceptor does not kill fleas, so Sentinel does more, which is why it costs slightly more.

Our Review of Interceptor and Sentinel

Both products are effective at preventing parasites from developing using the broad-spectrum ingredient milbemycin oxime. When given on a regular, monthly dose, fur babies do not develop heartworms. The medications have different ingredients that fight against fleas and other parasitic worms.

Both products work quickly and continue to work as long as dosages are given regularly. If you want to provide ample protection against heartworms and other parasitic worms, the Interceptor is the best choice. Interceptor does not offer protection against fleas, so your fur baby will need another medication.

Cats can get heartworms, even though it is rare. So, veterinarians do occasionally prescribe Interceptor for them.

If you are looking for a medicine that prevents both heartworms and fleas, then the best choice for dogs is Sentinel. While Sentinel does protect against heartworms, the medication does not prevent all worms to the same degree that Interceptor does. Sentinel is a better choice for dogs, because of the worms it treats. If you want to use it for your cat, talk to your veterinarian.

Both come highly recommended by veterinarians, and the FDA approves both. They both need to be prescribed by veterinarians, so if cost is a factor, you should consider the vet appointment price.

Flea Treatment FAQs

How often do you give your pet Sentinel tablets?

Once per month.

What parasites does Sentinel control?

Spectrum protects against fleas, heartworms, roundworms, hookworms, and whipworms. It also offers protection against tapeworms.

How often do you give your pet Interceptor tablets?

One per month.

What parasites does Interceptor control?

Interceptor prevents heartworm, controls hookworms, and removes roundworms and whipworms.

What size dogs can take Sentinel?

The smallest dosage is for dogs under 10 pounds, while the largest dosage is for dogs that weigh 100 pounds. If your dog is outside of that range, talk to your veterinarian for a recommended dosage.

What size dogs can take Interceptor?

Dogs that weigh between 2 pounds and 100 pounds can take Interceptor. If your dog is larger than 100 pounds, talk to your veterinarian about the appropriate dosage.

What size cats can take Interceptor?

Cats that weigh between 1.5 pounds and 25 pounds can take Interceptor. If your cat weighs more than 25 pounds, speak with your veterinarian for the best advice.

Do these medications have flavors?

Yes. Both have meat flavors. Interceptor tastes like chicken. Sentinel tastes like bacon and beef.

Are the medications chewable?

They are both chewy, so dogs and cats can take them without issue. Interceptor will dissolve in soft food, so you have an alternative if your pet fights taking it.

What are the side effects of these medications?

Sentinel’s side effects include vomiting, lethargy, diarrhea, urticaria, anorexia, convulsions, and more. Interceptor’s side effects include vomiting, lethargy, ataxia, weakness, hyper-salivation, and a few others. Because the medications have similar ingredients, they have several similar side effects.

What is the minimum age for animals who take these medications?

Dogs should be at least four weeks old. Kittens should be at least six weeks old before taking these medications.


Veterinarians regularly recommend both Sentinel and Interceptor to prevent parasitic worms from infesting fur babies. The FDA has approved Sentinel for dogs and Interceptor for cats and dogs. Veterinarians must prescribe them, but the medications are affordable, with monthly costs between $6 and $13.

While both medications have side effects, they are minimal, especially when compared to the health problems that come from heartworms. Both medications have two active ingredients. They share milbemycin oxime, which vets prescribe to protect against heartworm infections. The other drugs manage the fleas and other worms.

If you are looking for a broad-spectrum parasitic medication, Sentinel is a wise choice as it protects against fleas and most worms. Sentinel is not recommended for cats, even though it has flea protection. Interceptor is a smart choice to protect cats against heartworm, even though cats are less likely to develop the problem when compared to dogs.

Both of these medications are good choices to improve your pet’s health. However, many pet parents use these drugs with other flea-prevention medications to give their pets a full defense against harmful parasites.

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