Sentinel for Dogs

PetMD’s medications content is written and reviewed by veterinary professionals to answer common questions about how medications work, their side effects, and what species they are prescribed for. This content should not replace advice from your veterinarian. 

What Is Sentinel Used for in Dogs?

Sentinel is a monthly chew for dogs that helps prevent heartworm disease and helps control fleas by preventing flea eggs from hatching. It also treats and controls common intestinal parasites, including hookworms and whipworms. 

Sentinel Spectrum contains the same heartworm prevention, flea egg control, and intestinal parasite coverage as Sentinel, plus an additional ingredient to treat and control tapeworm infections.  

Is Sentinel FDA-Approved for Dogs? 

Yes, Sentinel and Sentinel Spectrum are FDA-approved for use in dogs for external and internal parasite protection.  

Speak with your veterinarian about whether Sentinel is right for your pet. 

Sentinel Considerations for Dogs

Sentinel is intended for use in dogs:  

• Weighing more than 2 pounds  

• Older than 4 weeks of age 

Sentinel Spectrum is intended for use in dogs:  

• Weighing more than 2 pounds  

• Older than 6 weeks of age 

All dogs should be tested for existing heartworm infection prior to starting treatment with Sentinel or Sentinel Spectrum. 

Dogs with existing heartworm infections should be treated to remove the adult heartworms before starting this medication. Placing a dog with an active heartworm infection on this medication can cause a serious allergic reaction. 

How Does Sentinel Work in Dogs?

Sentinel and Sentinel Spectrum share two of the same ingredients:  

• Milbemycin oxime: The main active ingredient in both Sentinel and Sentinel Spectrum, milbemycin paralyzes heartworms, roundworms, hookworms, and whipworms, causing them to die. 

• Lufenuron: The other active ingredient in Sentinel and Sentinel Spectrum, lufenuron targets flea eggs and prevents them from developing and hatching. Because lufenuron does not kill adult fleas, it’s typically used in combination with other medications to treat active flea infestations. 

Sentinel Spectrum contains one additional ingredient that Sentinel does not:  

• Praziquantel: This third active ingredient in Sentinel Spectrum, praziquantel causes tapeworms to be paralyzed and die.  

How Do You Give Sentinel to Dogs?

Follow the directions on the drug label or as provided by your veterinarian. 

• Both Sentinel and Sentinel Spectrum are given by mouth once a month.  

• Always give this medication with a meal or immediately after a meal.  

• This tablet is designed to be chewed, not swallowed whole. It can be broken into pieces or placed in a small amount of food to encourage chewing. 

• Watch your dog to make sure they eat the whole tablet or consume the whole chew. If your dog did not consume all of the tablet, redosing with a new chewable is recommended.

What Happens If You Miss a Dose of Sentinel? 

Speak with your veterinarian about what to do if a dose is missed.  

Generally, your vet may instruct you to give it when you remember and resume your normal dosing schedule. 

It’s important to give this medication monthly year-round, so be sure to maintain a ​consistent ​dosing schedule every 30 days. If the interval between doses exceeds 30 days, this puts your dog at risk of contracting parasites.   

Do not give extra or double doses. 

What Are the Side Effects of Sentinel in Dogs?

Side effects in Sentinel or Sentinel Spectrum are uncommon, but they may include: 

• Vomiting 

• Diarrhea 

• Loss of appetite 

• ​​Lethargy​ 

• Generalized itching 

• Hives 

• Lack of coordination 

• Drooling 

• Weakness 

• Seizures 

Human Side Effects 

Humans should never take medication prescribed for pets, and pets should not be given medication prescribed for humans. Dosages often differ significantly. 

If you accidentally ingest a pet medication, seek medical attention or call Poison Control at 800-222-1222. 

Monitoring Your Pet 

Dogs should be tested for heartworm infection before starting Sentinel or Sentinel Spectrum. If a dog tests positive, adult heartworm treatment is required before beginning this medication.   

Because Sentinel and Sentinel Spectrum kill immature heartworm larvae, dogs with an existing infection may experience a reaction after dosing. Your veterinarian may recommend additional monitoring or testing based on your dog’s health status and medical history.   

When Should You Call Your Veterinarian? 

Call your veterinarian if you see any of the following, or if you have additional questions or concerns about the use of Sentinel or Sentinel Spectrum: 

• Severe side effects 

• Your pet’s condition worsens or does not improve  

• You suspect an overdose 

What Happens If a Pet Overdoses on Sentinel?

The most common symptoms of an overdose with Sentinel or Sentinel Spectrum include:  

• ​​     ​​Tremors​ 

• ​​     ​​Lethargy​ 

• ​​     ​​Lack of coordination​ 

• Shallow breathing 

• ​​     ​​Drooling ​ 

• ​​     ​​Loss of appetite ​ 

• ​​     ​​Vomiting​ 

If you suspect an overdose, seek emergency veterinary care or contact an animal poison control center. Consultation fees may apply. 

• Pet Poison Helpline: 855-764-7661 

• ASPCA Animal Poison Control: 888-426-4435 

How Should Sentinel Be Stored for Dogs?

Keep the following storage tips in mind for this medication:  

• Sentinel and Sentinel Spectrum should be stored at controlled temperatures between 59–77 F (15–25 C). 

• Keep the medication in the provided blister pack until you use it to protect it from moisture and light.  

• As with any other medication, keep it out of reach of children and pets.