Sentinel Products for Fleas and Heartworms in Dogs

Medically Reviewed by Joshua Conrad, PharmD on October 20, 2024
Written by Kathleen Claussen, DVM
5 min read

The Sentinel line of products (manufactured by Merck Animal Health) includes chewable tablets (products that are given by mouth) for fleas, heartworms, roundworms, hookworms, and whipworms in dogs.  Sentinel products are approved by the FDA for various antiparasitic uses in dogs depending on which product is being used.  These uses include the control of flea infestations, prevention of heartworm disease, and treatment of intestinal roundworms, hookworms, and whipworms.

There are two Sentinel products for fleas and heartworms in dogs: Sentinel Flavor Tabs and Sentinel Spectrum Chews.  Both of these products contain milbemycin and lufenuron. Milbemycin is a macrolide antiparasitic used for heartworm prevention and for the removal and control of roundworms, hookworms, and whipworms in dogs and puppies.  Lufenuron is a chitin synthesis inhibitor and insect growth regulator used for control of fleas in pets.  Sentinel Spectrum Chews have the added ingredient of praziquantel.  Praziquantel is used for the treatment of tapeworms in pets.

Sentinel Flavor Tabs are labeled for one month (30 days) of protection against fleas, heartworm disease, roundworms, hookworms, and whipworms.  Sentinel Spectrum Chews are labeled for one month (30 days) of protection against fleas, heartworm disease, roundworms, hookworms, whipworms, and tapeworms.  Both products prevent flea eggs from hatching, but they do not kill adult fleas.

Sentinel products are usually well tolerated in dogs.  There is minimal risk for overdose, side effects, or drug interactions if used as labeled or as directed by your veterinarian.

Sentinel products are available from your veterinarian or with a prescription from your veterinary pharmacy.

Sentinel Flavor Tabs are pork liver flavored chewable tablets that you give your dog by mouth once a month (every 30 days).  Sentinel Spectrum Chews are beef and bacon flavored chewable tablets you give your dog by mouth once a month (every 30 days).  The chews should be given with a meal or immediately after your dog or puppy has eaten a meal.  Sentinel chews should be eaten completely to be effective.  Dogs and puppies should weigh at least 2.0 pounds (0.9 kilograms) to take either product.  They should be at least 4 weeks old for Sentinel Flavor Tabs and at least 6 weeks old for Sentinel Spectrum Chews.

Always follow your veterinarian’s directions for giving medicines to animals.  Remember to tell your veterinarian about any medicines, vitamins, supplements, or herbal therapies that you are giving your pet. Talk to your veterinarian before stopping any pet medicines.  

  • Milbemycin/lufenuron (Sentinel Flavor Tabs) is licensed by the FDA to protect against fleas, heartworms, roundworms, hookworms, and whipworms.
  • Adding praziquantel (Sentinel Spectrum Chews), extends the previously mentioned protection to include tapeworms.
  • Sentinel products can be given to dogs and puppies that weigh at least 2 pounds (0.9 kilograms).
  • Dogs and puppies can be as young as 4 weeks old to take Sentinel Flavor Tabs and as young as 6 weeks old to take Sentinel Spectrum Chews.

You and your veterinarian should monitor your pet for signs that the medicine is working (absence of live fleas) as well as for side effects of the medicine.  There is no routine lab monitoring needed with Sentinel products.  If Sentinel products are used for intestinal parasites, follow-up fecal (stool) tests may be checked.  

Before giving Sentinel products, dogs need to have a negative heartworm test.  The heartworm test should then be repeated yearly.  If there are missed doses of a Sentinel product, a heartworm test should be repeated before restarting the medication and then again in six months.  

Do not use a Sentinel product in an animal that is allergic to its ingredients.  Do not use Sentinel products in dogs below the minimum age or weight on the product label.  Use Sentinel products with caution in pregnant or nursing dogs.  Use with caution in dogs that have not been tested for heartworm disease.  Dogs that are infected with heartworms can have shock-like reactions if they take milbemycin.

Side effects are rare if the products are used according to the labeled instructions.  Side effects with Sentinel products may include:

  • Vomiting
  • Diarrhea (loose stool)
  • Decreased appetite
  • Pruritus (Itching)
  • Lethargy (tiredness)
  • Red skin or rash

Serious side effects are very rare with Sentinel products, but they may be a sign of an overdose or toxicity.  This is especially of concern in dogs with a genetic mutation called MDR1.  Serious side effects may include:

  • Lack of energy or weakness
  • Stumbling or collapse
  • Seizures or coma
  • Big (dilated) pupils
  • Excessive drooling

If you suspect that your pet is having a serious side effect or may have been overdosed, call your veterinary clinic immediately. If it is outside of regular office hours, you may contact a local emergency veterinary hospital or an animal poison control center. Note that fees may apply for emergency consultation.

You can reach the ASPCA Animal Poison Control Center at 888-426-4435 or the Pet Poison Helpline at 855-764-7661.

Using multiple medicines can sometimes change how your pet’s medicines work or increase your pet’s risk for serious side effects.  Always tell your veterinarian about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements that your pet is using.

Sentinel products were used safely in studies with adulticides (medicines to protect against adult fleas), vaccines, deworming products, antibiotics, and steroids.

  • Keep Sentinel products out of the reach of children.
  • Wash your hands with soap after handling Sentinel products.
  • Do not handle Sentinel products if you are allergic to any of the ingredients.

Sentinel products are well tolerated by animals and the risk of an overdose is low.  If you are concerned your pet is having an adverse reaction or if you think your pet has gotten more medicine than intended, call your veterinarian or veterinary emergency clinic immediately.

If your pet misses a dose, give the dose when you remember and then restart the dosing interval from that date.  Do not double the dose of the medicine.  

If more than eight weeks have passed since the last dose of a Sentinel product, start the monthly chew again.  Your dog will need to have a heartworm test performed in six months to determine if there is heartworm disease.  It takes six months from the bite of an infected mosquito till a dog may test positive for heartworm disease.

Store Sentinel products in the original packaging at room temperature.  Protect them from light.  Be careful about disposal of Sentinel products as they can be toxic to wildlife.