Every time our dogs explore the outside world, they get exposed to a variety of microorganisms that can pose a threat to their general wellbeing. While there are many anti-parasite preparations in the market in the form of topical applications, flea and tick collars, and even medicated soaps and shampoos, one of the most trusted names when it comes to flea and heartworm preventatives is Sentinel. In this post we shall take a closer look at this particular product and learn more of its mechanism of action and why many vets and pet owners alike actually recommend this product over other brands.

dog in grass

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What is Sentinel for Dogs

Sentinel is a chewable tablet that is beef-flavored and given to dogs once every 30 days. It is an antiparasitic medication that is formulated and developed primarily for the prevention and management of fleas and heartworm infestations. It contains two very important active ingredients for which we are going to explore further in this post. These include Milbemycin Oxime and Lufenuron. In a gist, what Sentinel does is that it puts a stop to the reproductive capabilities of adult fleas so they will no longer be able to lay their eggs. Additionally, as a heartworm preventative, circulating milbemycin oxime has been shown to disrupt the nervous system of heartworm larvae, leading to their demise.

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How Sentinel for Dogs Exerts its Antiparasitic Action

The key to Sentinel’s effectiveness is its combination of active ingredients: Milbemycin Oxime and Lufenuron.

  • Milbemycin Oxime

This chemical compound is a lot similar to another class of antiparasitic preparations for dogs, the Avermectins. However, Milbemycin Oxime has a much longer half-life than avermectins. This compound works by opening certain channels in the neurons and muscle cells of susceptible organisms which results in cellular hyperpolarization. This means that nerve impulses are effectively blocked so different organs of the affected organism don’t receive these signals. This leads to their death as they don’t receive the necessary stimulus needed for continued growth and development. 

Milbemycin is primarily designed to help prevent and / or manage intestinal parasitism caused by susceptible organisms belonging to the Nematode classification of intestinal helminthes or parasites. Nematodes are also known as round worms. Three of the most common round worms known to infect dogs include the following.

  • Dirofilaria immitis (a heartworm)
  • Ancylostoma caninum (a hookworm)
  • Trichuris vulpis (a whipworm)

The drug is also active against mites, particularly those belonging to Sarcoptes and Demodex genera. These parasitic arthropods include Sarcoptes scabiei (the one producing scabies) and Demodex canis (which can cause red mange or demodectic mange).

For it to be effective in its intended purpose, experts recommend giving 0.23 milligrams for every pound of a dog’s body weight. This means that if you have a 20-pound pooch, you need to give 4.6 milligrams of Milbemycin Oxime to exert its antiparasitic, antihelminthic effects.

  • Lufenuron 

Lufenuron is classified as an insect development inhibitor. This chemical is also found in the dog flea medication Program and is primarily designed to disrupt the reproductive capabilities of female adult fleas. Lufenuron is essentially stored in the dog’s subcutaneous layer of fat. When adult fleas bite the dog, they eventually suck Lufenuron into their own bloodstream and transfer the chemical to their growing eggs. Some of the Lufenuron are also distributed to feeding larvae.

Technically, what Lufenuron does is that it prevents the flea larvae from producing chitin which is a very important ingredient for the development of a very sturdy and very resilient outer shell. Because there is no outer protective covering for the developing larvae, its internal organs are essentially exposed to the outside air where dehydration can hasten the rate of its demise. This occurs right upon hatching or the shedding of the larvae’s old and smaller outer shell.

Because Lufenuron inhibits the production or synthesis of chitin, it is also deemed effective in the mitigation of fungal infections since about a third of the cell wall of fungal species is made of chitin.

The average dosing of Lufenuron is currently at 4.55 milligrams per pound of a dog’s weight. In our 20-pound dog example above, this means you will need about 91 milligrams of Lufenuron. Combined, what you are looking for is a Milbemycin oxime-Lufenuron blend of 4.6 mg and 91 mg. Of course, this is just the recommended dose. Other factors may have to be considered by your veterinarian whether to increase the dose or to decrease it altogether.

It is through the inherent activities of these two active ingredients that Sentinel for dogs can provide its exceptional protection against heartworms, hookworms, whipworms, other round worms, fleas, mites, and yeast. It is this broad spectrum of activity that makes Sentinel a preferred brand.

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Difference from Sentinel Spectrum

There is another variant of Sentinel, the Sentinel Spectrum that provides an additional ingredient to its Milbemycin oxime and Lufenuron formulation. Sentinel Spectrum contains Praziquantel to give it the added benefit of killing Cestodes or tapeworms particularly the following.

  • Dipylidium caninum
  • Echinococcus multiocularis
  • Echinococcus granulosus
  • Taenia species
  • Spirometra mansonoides
  • Diphyllobotrium latum

These parasites often live and develop in fleas that reside in dogs. Praziquantel is known to expose the cell membranes of these microorganisms to calcium which leads to abnormal yet powerful contractions. This dislodges them from their sites of attachment where they are easily destroyed by the dog’s phagocytotic mechanism.

Benefits of Giving Sentinel for Dogs

Based on what we know so far about Sentinel for dogs, it can provide the following benefits.

  • Protection against heartworms particularly Difilaria immitis
  • Controls adult intestinal hookworms like Ancylostoma caninum
  • Eliminates whipworms from the dog’s intestines especially Trichuris vulpis
  • Controls adult round worms especially Toxascaris leonina and Toxocara canis
  • Prevents flea eggs and larvae from maturing
  • Prevents the development of scabies and demodectic mange
  • Protects dogs against yeast infections
  • Protects dogs against tapeworm infections, if you choose the Sentinel Spectrum

These benefits are exceptional for a single product since you would normally require a variety of products to address all of these concerns. This is one of the many reasons why a lot of pet owners and veterinarians provide Sentinel to their dogs. 

Drawbacks of Sentinel

As effective as Sentinel is in preventing and controlling a variety of parasitic problems in dogs, it does have some particularly distressing drawbacks. It is true that when it comes to preventing, controlling, and managing intestinal parasitic and heartworm infections, Sentinel’s Milbemycin oxime is without equal. Unfortunately, its Lufenuron component leaves some things to be desired. We have listed below some of the more pressing concerns related to Sentinel for dogs.

  • Does not kill adult fleas 

It should be recalled that Sentinel’s Lufenuron component is an insect growth inhibitor or insect development inhibitor. Technically, as we have already described above, it incorporates itself into the reproductive system of the adult female flea. Once in the system, it now wreaks havoc in the natural process of chitin formation. This leads to especially vulnerable juvenile fleas because they don’t have the necessary protection against the harsh environment. Some may grow but, in their sufficiently compromised state, they will lose the ability to reproduce.

The point is that if you already have massive flea infestation in your dog, Sentinel should always be combined with an adulticide, an insecticide that will kill adult fleas. At any rate, these chemicals should offer you a more well-rounded approach in the control of fleas on your pet. Sentinel can halt the development of flea eggs and larvae that are not affected by adulticides while the latter products can help eliminate and remove the adult flea population from your dog.

  • Does not repel fleas 

Just as Sentinel doesn’t kill adult fleas, it won’t be able to repel them either. This is because its active ingredients are absorbed in the bloodstream of dogs. These do not permeate the outer layer of the skin so as to create an invisible shield like some other flea and tick repellents do. So, if your pooch happens to go out of the home and venture outside where fleas are known to inhabit, chances are it will still be bringing quite a number of these critters upon its return. The good thing though is that these fleas will not be able to reproduce once they got the Lufenuron in their system.

  • Requires fleas to bite dogs first 

The unique formulation of Sentinel requires fleas to bite into the skin first before any significant effects can be obtained. Unfortunately, if your mutt happens to have allergies to flea bites resulting in flea bite dermatitis, a different flea control product may have to be used.

  • Requires veterinary prescription 

Unlike other products that you can simply obtain from your local pet store Sentinel for dogs requires a prescription from your vet. This is because of the Milbemycin oxime component of Sentinel. It is imperative to ascertain that your dog does not have any existing heartworms as giving Sentinel at this stage can increase the risk of labored breathing, lethargy, increased salivation, and vomiting in dogs. These occur because of the death and eventual release of baby heartworms in the blood. As such, veterinarians will have to perform a negative heartworm test first.

Side Effects of Sentinel that You Have to be Aware Of

It is important to understand that no matter how safe a medication is the mere fact that it is not a natural part of the body can elicit some physiologic effects other than what is intended. The same is true with Sentinel. The following side effects have been observed in dogs taking Sentinel.

  • Diarrhea
  • Depression
  • Drooling
  • Loss of appetite
  • Lethargy
  • Vomiting
  • Staggering
  • Seizures

Most of these side effects are rare and should resolve within 24 hours after the administration of Sentinel. However, in cases where the manifestations persist beyond the first 24 hours, you should consult with your vet at once.

medication for dogs

How Sentinel is Administered

Currently, Sentinel for dogs is available in chewable tablet form and flavored with beef. This helps facilitate the easier administration of the medication as dogs have a natural liking to beef. Furthermore, since the preparation is made to look and taste like a doggie treats, giving them to dogs should be very easy. The Spectrum version of Sentinel is available in a blend of bacon and beef, making it even more palatable and enjoyable to pooches.

Sentinel is given every 30 days all year round. If you prefer to give it seasonally, it should be administeredwithin 30 days of the first exposure to fleas and other vectors. It should also be given with food or immediately after a meal as this helps improve the absorption rate of Lufenuron. It is important to supervise your dog while consuming the chewable tablet so it gets all of it.

If your dog missed a dog, you should give it Sentinel at the soonest possible time and making this date your new 30-day schedule. For example, if the original schedule is every 5th day of the month, but you missed it and you gave your dog Sentinel on the 8th day of the month, then succeeding doses should now follow the new schedule of every 8th day of the month.

It is also important to have your pooch tested for heartworm infection even before starting it on Sentinel or any other heartworm medication. If your dog was off Sentinel for no more than 6 months, you can restart the medication any time but should follow this with heartworm testing after 6 months.

Availability of Sentinel for Dogs

Sentinel for dogs is color-coded to help facilitate easier selection of the appropriate variant for your pooch.

  • Brown – Dogs weighing between 2 and 10 pounds
  • Green – Dogs that weigh 11 to 25 pounds
  • Yellow – Dogs weighing 26 pounds to 50 pounds
  • White – Pooches that weigh between 51 and 100 pounds

If you have a mutt that weighs more than 100 pounds, it is often recommended to give two doses of the correct or appropriate size. For instance, if you have a 120 pound pooch, then getting a White and Green variant should be sufficient.

Sentinel for dogs is an effective preventative against heartworm and intestinal parasitic infections in dogs. It is also an excellent way to control the population of fleas. Unfortunately, since it doesn’t kill adult fleas, other products may have to be used.

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Olivia Williams
Olivia is our head of content for MyPetNeedsThat.com, 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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