Sentinel for Dogs
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At a Glance
Combination of two active ingredients protects dog parasite infestations.
Lufenuron controls flea larvae reproduction.
Milbemycin is heartworm disease preventative & controls intestinal worms.
One chewable tablet per month is administered orally to work for the next 30 days.

Sentinel for Dogs

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At a Glance
Combination of two active ingredients protects dog parasite infestations.
Lufenuron controls flea larvae reproduction.
Milbemycin is heartworm disease preventative & controls intestinal worms.
One chewable tablet per month is administered orally to work for the next 30 days.

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Merck Animal Health Logo

Ultimate Guide to Sentinel for Dogs

Meet the Powerful Parasite Preventer: Sentinel for Dogs!

Sentinel for Dogs is the veterinarian-approved dog medication that protects your dogs from various dangerous tiny parasites, internal and external. Sentinel is a monthly, chewable oral tablet that also prevents vicious heartworm disease that is transmitted from mosquito bites. Sentinel ensures that your pup is in their healthiest condition.

How does Sentinel for Dogs work?

Sentinel for Dogs is a medication with two active ingredients (Lufenuron and Milbemycin Oxime).

Lufenuron is an insecticide that distributes into the dog's body fat which the adult flea will eat and pass on to its eggs. As a pesticide and insect growth regulator (IGR), it inhibits the development of chitin which builds a larval flea's exoskeleton. When they hatch, the flea larva dies when its inner organs are exposed to air.

The second active ingredient, milbemycin oxime, is a powerful parasiticide and an anthelmintic, or dewormer. It is 100% effective heartworm disease preventative. It also controls three dangerous intestinal worms (i.e., adult roundworms, hookworms, and whipworms).

Because Sentinel for Dogs is a heartworm disease preventative, make sure every dog is tested by your veterinarian before prevention therapy or using Sentinel.

How is Sentinel for Dogs administered?

Sentinel for Dogs is administered orally once a month and protects your dog for the next 30 days. These beef-flavored chewable tablets can be used as dog treats or, most effectively, eaten with the dog's food. Sentinel is used year-round for maximum prevention effectiveness.

Body Weight Milbemycin Oxime/Lufenuron per Tablet (mg) No. of Tablets
2 - 10 lbs.2.3/46One
11 - 25 lbs.5.75/115One
26 - 50 lbs11.5/230One
51 - 100 lbs.23/260One
What dogs should not be given Sentinel?

Dogs that are below 6 weeks old or weigh less than 2 pounds. Breeding, pregnant, and lactating females have not been evaluated.

What are the potential side effects of which you should be aware?

Test for heartworm disease before deworming therapy or before using Sentinel. Sentinel's most common unfriendly reactions reported are vomiting, diarrhea, itching, decreased appetite, hives, and seizures. Contact your veterinarian if any effects occur.

Frequently Asked Questions
What Is Sentinel for Dogs?

Sentinel protects your dog from internal and external parasites. It is a veterinarian-approved medication. Sentinel tablets are to be administered monthly and come as chewable tablets.

Sentinel tablets also help prevent your dogs from heartworm disease - a disease spread by mosquito bites. Sentinel keeps your dog in a healthy condition.

Is Sentinel Safe for Dogs?

Pet owner reviews suggest the higher levels of trust that they have in this medication. The average rating of the tablets is more than 4.5 out of 5 stars.

Most dog owners prefer Sentinel to treat their pet's heartworm and flea problems over other available medication options.

If your dog is below 6 weeks or its weight is less than 2 pounds, avoid administering Sentinel to it. Also, keep in mind that Sentinel is still due for evaluation with lactating, pregnant, and breeding females.

What Does Sentinel for Dogs Do?

Sentinel protects your dog from internal and external parasites. It is a veterinarian-approved medication. Sentinel tablets are to be administered monthly and come as chewable tablets.

Sentinel tablets also help prevent your dogs from heartworm disease - a disease spread by mosquito bites. Sentinel keeps your dog in a healthy condition.

Who Makes Sentinel for Dogs?

Merck Animal Health makes Sentinel for Dogs.

Does Sentinel for Dogs Kill Ticks?

Sentinel can act as an insect regulator for your dog. The medication effectively controls flea larvae D. immitis.

Sentinel discourages the growth of fleas from flea eggs but is not effective against adult fleas. Sentinel does not kill ticks in your dog. Sentinel can control worms growing inside the body of your dog.

Except for tapeworms, Sentinel can prohibit the growth of roundworms, hookworms, whipworms, and heartworms.

How Does Sentinel for Dogs Work?

Sentinel has two active ingredients, namely Lufenuron and Milbemycin Oxime.

Lufenuron is a pesticide and insect growth regulator or IGR. Once your dog ingests a Sentinel tablet, Lufenuron distributes into your dog's body fat. The adult flea feeds on this body fat and passes it while laying eggs.

IGR inhibits the larval flea's exoskeleton development. The flea larvae die post-hatching from exposure of internal organs to air.

Milbemycin Oxime is a dewormer, an anthelmintic, and a powerful parasiticide.

Sentinel can prohibit the growth of the three dangerous intestinal worms i.e. roundworms, hookworms, and whipworms, because of milbemycin oxime.

Contact your veterinarian for testing your dog before starting administration of Sentinel.

How Is Sentinel for Dogs Administered?

Sentinel is an oral medication. Use of these beef-flavored chewable tablets with food is advised. Veterinarians often advise using Sentinel all year round to give your dog maximum protection.

What Are the Side Effects of Sentinel for Dogs?

Contact your veterinarian for testing your dog before starting administration of Sentinel.

The most common side effects of Sentinel include - seizures, vomiting, itching, hives, diarrhea, and decreased appetite. Contact your dog's veterinarian immediately if any effect occurs.

Can You Break Sentinel Tabs for Dogs?

A tablet that is scored' can be easily divided. These are created by the manufacturer as a sign to mean okay to split'. The split line also helps to break the medicine evenly.

Breaking the medicine in two or crushing the medicines helps to administer them to the pets easily. If the tablet is too large for your dog to chew, breaking it helps them take it easy.

Splitting the Sentinel tablets is not advisable by the manufacturer. Any tablet used to treat flea infestation or kill them should not be split unless your dog's veterinarian suggests doing so.

What Is in the Sentinel Tablets?

Milbemycin Oxime and Lufenuron are both protectors of your dog against internal and external parasites.

What Is the Difference Between Sentinel and Sentinel Spectrum?

Milbemycin Oxime and Lufenuron- are the active ingredients for both Sentinel and Sentinel Spectrum. Along with the treatment of other worms, Sentinel can also treat tapeworms because of the added ingredient - anthelmintic praziquantel.

So a Sentinel Spectrum can treat all kinds of worms, namely tapeworms, hookworms, roundworms, whipworms, and heartworms.

Is There Sentinel for Cats?

Sentinel for Dogs was only made to be administered to dogs, and therefore it is not for cats.

Is Sentinel for Puppies?

Sentinel can be administered to puppies that are at least 6 weeks old and weigh 2 pounds.

How Long Does It Take for Sentinel for Dogs to Work?

Post ingestion, Sentinel starts to work immediately. The dissemination of the medicine in the dog's body fat helps in a fast action against heartworms.

Concluding Thoughts

The most important thing that you should know about Sentinel is its power to protect your dog from tiny parasites and the dangerous heartworm disease, internal and external parasites.

DISCLAIMER: Ask your veterinarian or consult with one of our pet care specialists at 1-800-844-1427. This informative article is not meant to substitute for the diagnosis, treatment, and professional advice from your veterinarian or other qualified professionals regarding a medical condition.

  • Merck Animal Health Brand
  • Heartworm & Deworming Pharmacy
  • Flea & Tick Pharmacy
  • Merck Animal Health Manufacturer
  • Oral Application
  • Dog Pet Type

Can Sentinel Be Used in All Breeds of Dogs?

Sentinel is generally considered safe for most dog breeds and puppies over four weeks of age and weighing above 2 pounds.

Is Sentinel Effective Against All Types of Worms in Dogs?

No, it is not. However, it protects dogs against six parasites, including heartworms, fleas, hookworms, roundworms, whipworms, and tapeworms. While Sentinel is effective against these parasites, it may not provide complete coverage against all types of parasites. Additional treatment may be necessary if your dog has been diagnosed with a specific parasite.

Can Sentinel Be Used as a Preventative Measure Against Heartworm Disease?

Yes, Sentinel can be used as a preventative measure against heartworm disease in dogs. The active ingredient, milbemycin oxime, is a broad-spectrum antiparasitic agent effective against heartworms. When given to dogs once a month, Sentinel helps to prevent heartworm disease by killing the immature stages of the heartworms before they can develop into adults.

Does Sentinel Require a Prescription From a Veterinarian?

Yes, Sentinel does require a prescription from a veterinarian. Sentinel is a medication that contains prescription-only active ingredients, and it is important to ensure that the medication is used safely and effectively. A veterinarian can determine if Sentinel is appropriate for your dog based on age, weight, health status, and other factors.

How Does Sentinel Compare to Other Deworming Medications for Dogs?

Compared to other deworming medications for dogs, Sentinel has several advantages. First, it offers comprehensive protection against multiple parasites, which can be more convenient and cost-effective than using multiple medications to treat different parasites. Additionally, the active ingredients in Sentinel are considered safe and well-tolerated by most dogs, with minimal side effects reported. Sentinel also offers unique benefits that set it apart from other deworming medications. The lufenuron component of Sentinel is an insect growth regulator that prevents flea eggs from hatching, which can help to control flea infestations and prevent the transmission of tapeworms.

Can Sentinel Be Used in Old Dogs?

Yes, it can. Sentinel Flavor Tabs are indicated for use in dogs and puppies at least four weeks of age and weighing two pounds or more.

Can Sentinel Be Used in Dogs With a History of Digestive Issues?

Yes, Sentinel is considered safe and well-tolerated in most dogs, including those with a history of digestive issues. However, as with any medication, there is a risk of side effects or adverse reactions, and some dogs may be more susceptible to these effects.

Can Sentinel Be Used in Dogs With a History of Pancreatitis?

Milbemycin oxime, one of the active ingredients in Sentinel, has been associated with rare reports of gastrointestinal side effects, including vomiting and diarrhea. These side effects may be more concerning in dogs with a history of pancreatitis, as the condition can make them more susceptible to gastrointestinal upset and other complications. Lufenuron, the other active ingredient in Sentinel, is not expected to cause issues in dogs with pancreatitis, as it does not affect the pancreas or digestive system.

Can Sentinel Be Used in Dogs With a Compromised Immune System?

Yes, Milbemycin oxime and lufenuron, the active ingredients in Sentinel, are generally considered safe and well-tolerated in most dogs, including those with compromised immune systems.

Can Sentinel Be Used in Dogs With a History of Seizures or Neurological Issues?

Yes, it may be used but under strict vet supervision. This is because milbemycin oxime, one of the active ingredients in Sentinel, can have neurological side effects in rare cases. These side effects include tremors, ataxia (lack of coordination), and seizures.

Can Sentinel Be Used in Working Dogs or Dogs With an Active Lifestyle?

Sentinel is typically regarded as secure and well-tolerated by the majority of dogs. Any drug carries the potential for allergic responses, though. Itching, swelling, respiratory difficulties, vomiting, and diarrhea are all potential symptoms of an allergic response. Before administering Sentinel to your dog, it's essential to inform your doctor if they have a history of allergic reactions to medicines.

How Frequently Does Sentinel Need to Be Given to Maintain Effectiveness?

Sentinel should be given once a month to maintain its effectiveness in preventing heartworm disease, controlling intestinal parasites, and preventing flea infestations by inhibiting flea egg development.

Can Sentinel Be Used Year-Round or Only During Certain Seasons?

Sentinel can be used year-round to offer continuous defense against fleas, gut parasites, and heartworm disease. Even during seasons when flea infestations may be less frequent or the dog is not outdoors as much, it is crucial to administer Sentinel on a regular monthly schedule and not skip any doses.

What Should I Do if My Dog Vomits After Taking Sentinel?

If your dog vomits shortly after taking Sentinel or any other medication, it's important to contact your veterinarian for guidance. Your veterinarian may recommend monitoring your dog's condition and observing for any signs of adverse effects, or they may recommend giving another dose later. However, giving Sentinel with a full meal is recommended to help reduce the risk of vomiting or other adverse effects.

Sentinel for dogs contains Milbemycin oxime and Lufenuron.



The controlling of the flea infestation among the pets like cats, dogs, rabbits, and ferrets happens with the insect growth regulator Lufenuron. The disruption of the chitin synthesis helps to ensure flea control with the help of this benzoylphenylurea drug, Lufenuron. The outer cell wall of the fungi has the critical component in the form of chitin, and the drugs help disrupt its synthesis. The frequent occurrence of the drug with other medications like praziquantel or milbemycin helps to increase its efficacy.ย 

Special Precautions

The pets that have known cases of allergy should have the drug. Caution is advisable for pets that are under the age of 6 weeks. It is a safe drug for pets in their breeding, lactating, and pregnant stages.


Predatory insects have a detrimental impact on the actions of the drug. These species can include the Pilophorus typicus, Ceraeochrysa Cubana Hagen, lacewing, bugs, and Orius laevigatus. Both the drug's actions in terms of its ingestion in the form of oral medication or topical application are equally potent.

Mechanism of Action

The classification of the drug as an insect development inhibitor works to interfere with the chitin synthesis by deposition and polymerization. The drug is made available for fleas by oral medicine or via injection. It helps to reach the fleas via the blood and impacts their systems.

The eggs that these fleas hatches cannot develop into larva and thereby stop the cycle of the fleas. It comes out of the feces of the fleas unchanged, and if any larva consumes the same faces, its development into normal pupa does not happen.

Known Drug Interactions

A few interactions have been put forth via a new guideline recently. These suggest that therapeutic proteins like cytokine modulators and cytokines should be administered with the drug carefully. The impact of the CYP enzymes needs to be properly quantified. The combination of other therapy or drug administration should happen only after evaluating the interaction of both the drugs.

Brand/Generic Equivalents


Sentinel Flavor Tabs, an alternative to Trifexis, are used in dogs and puppies for treating heartworm diseases and infections caused by hookworm, roundworm, and whipworm. Sentinel Flavor Tabs also control external parasites like fleas by curbing the development of flea eggs, though, it cannot eradicate adult fleas. Its active ingredient of Lufenuron has insect development inhibiting properties, which prevents the flea egg from maturing into an adult insect.

Sentinel Flavor Tabs is a prescription medicine presented as chewable, flavored tablets. The dosage depends on the dog's body weight. The recommended dose of Sentinel for dogs 2-10 pounds is 2.3 mg / 46 mg, 11-25 pounds is 5.75 mg / 115 mg, 26-50 pounds is 11.5 mg / 230 mg and 51-100 pounds is 23 mg / 460 mg, administered once every month, all round the year. Alternatively, it could be given once every month from the onset of the mosquito season till the end of the season.

IMPORTANT SAFETY INFORMATION: Dogs should be tested for heartworm prior to use. In a small percentage of treated dogs, digestive, neurologic, and skin side effects may occur. For complete product information refer to the product insert.

Sentinel Flavor Tabs should only be used in dogs with a minimum body weight of 2 lbs and are at least four weeks of age or older. It should never be administered in animals that are hypersensitive to it. Animals should be tested for heartworms prior to the therapy as it can result in serious shock-like reactions in heartworm positive dogs. Since the microfilaria takes around six months to mature, it is advisable to test the dogs for heartworm disease just before starting this medication. Humans should maintain good personal hygiene as hookworm and roundworm infections could be easily contracted. Try to eradicate fleas on the pet and desist from feeding the pet, rodents or raw flesh or fish. The pet stools should be removed daily and the premises kept clean. The tablet should be removed from the original pack only at the time of administration.

Sentinel Flavor Tabs side effects are rare; some animals might display symptoms like depression, drowsiness, nausea, skin irritations, loss of appetite, drooling, diarrhea or seizures.

Administer Sentinel for dogs orally or crumble into food. A second treatment may be necessary.

*Cats 4 pounds and under: 1/2 tablet as a single dose

*5-11 Lbs: 1 tablet as a single dose

*11 pounds and over: 1 1/2 tablets as a single dose

Store Sentinel for dogs in a cool, dry place.

Ask your veterinarian or consult with one of our pet care specialists at 1-800-844-1427.

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian. Always seek the advice of your veterinarian or other qualified professional with any questions you may have regarding a medical condition. Never disregard or delay seeking professional advice due to what you may have read on our website. Our medications are FDA approved and/or EPA regulated when and as required by law.

Sentinel for Dogs is manufactured by Merck Animal Health
Option UPC/SKU
BROWN,2-10 lbs. 6 Month Supply 716688522115
GREEN,11-25 lbs. 6 Month Supply 716688522214
YELLOW,26-50 lbs. 6 Month Supply 716688522313
WHITE,51-100 lbs. 6 Month Supply 716688522412
BROWN, 2-10lbs. 12 Month Supply 716688621115
GREEN, 11-25lbs. 12 Month Supply 716688621214
YELLOW, 26-50lbs. 12 Month Supply 716688621313
WHITE, 51-100lbs. 12 Month Supply 716688621412

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