Muddy Puppy

To Break the Flea Life Cycle,
Use a Multilevel Approach

June 2022 by Dr. Keri Shaver

Do you remember the bad old days of flea control?

Not so long ago, pet owners visited us with massive infestations on their pets and in their homes. Those visible infestations caused anemia and flea allergy dermatitis, and could even bite the owners themselves.

Treatment was a major production: pet baths, carpet sprays, room bombs, yard sprays and collars, often with products that had questionable safety profiles and were only effective for days or even hours.

Worst of all, most owners had to go through the whole routine every year, sometimes several times each year. Dogs with severe flea infestations were, sadly, all too familiar in practice.

Lufenuron: a breakthrough in flea control

Then, in the 1990s, the world of flea control in veterinary medicine changed. Lufenuron, an insect development inhibitor, was the first product that could truly break the flea life cycle. Lufenuron is a benzoylphenylurea compound from a family of chitin synthesis inhibitors.1,2 Lufenuron prevents flea eggs from hatching, thus breaking the cycle of infestation and preventing and controlling flea infestations at home and on pets. As a tablet, it was clean, easy, and simple for pet owners to administer.

For those of us in practice at the time, lufenuron was a game changer. Finally we had something simple and effective to offer those suffering pets and their owners. After more than 25 years of use, it’s still highly effective today and can be the cornerstone of an effective flea control program that includes lufenuron coupled with a safe and effective flea adulticide.1

“No other product, treatment, or procedure improved my practice like lufenuron.” Rick Marrinson, DVM

Sneaky little creeps

The flea life cycle is fascinating; while most pet owners focus on the adult fleas they can see, few realize that the majority of the problem is off the pet in the stages that live in the home.

During a flea infestation, adult Ctenocephalides felis make up approximately 5% of the total flea population.3 Of these adults, the females are the main troublemakers.

After beginning to feed on the pet’s blood, females begin laying prodigious amounts of eggs: up to 50 per day.4 Thus the old saying, “two days, two fleas, 200 eggs.” Now multiply that by the dozens of fleas on an infested pet and by the number of days the infestation can persist. Suddenly your client is dealing with thousands of future fleas in the form of eggs, larvae, and pupae, in addition to the dozens or hundreds they may see on their badly infested pet.

A flea infestation is like a pyramid, with the earliest stages at the bottom and adults at the peak. Flea eggs normally make up about 50% of the total flea population in an infestation, and the larvae crawling around in the environment and feeding on flea feces that have fallen off the hosts are another 35%. The nearly indestructible pupae are another 10%, just waiting for movement or body heat from a potential new host nearby to trigger the emergence of new fleas. The adults visible on the pet are just the top 5%!3

Clearly, using a short-term adulticide alone is not a complete solution. The only way to knock down this pyramid is by attacking it at multiple levels. That’s why the most complete way to control fleas is through the use of both of an insect development inhibitor like lufenuron and a safe, effective, and long-lasting adulticide. SENTINEL® Brand Products and BRAVECTO® (fluralaner) provide that broad coverage you need.

“By prescribing lufenuron and an extended-duration isoxazoline like fluralaner, we get the best of all worlds: fast kill of adult fleas while preventing an environmental infestation.” Rick Marrinson, DVM

BRAVECTO®: killing today’s adult fleas

To prevent or control flea infestations, we must kill the adult fleas on the pet. In addition to being a source of eggs, and therefore new fleas, their bites can cause flea allergy dermatitis in susceptible pets. Visible fleas upset owners, and newly emerging fleas can also bite the owners themselves, causing allergic reactions in humans and transmitting disease. Because of this, the Companion Animal Parasite Council (CAPC) recommends that veterinarians consider flea infestations a public health concern when talking with owners.4

The newest class of flea adulticides, the isoxazoline-substituted benzamide derivatives, includes fluralaner, the active ingredient in BRAVECTO® (fluralaner) Chews and BRAVECTO® (fluralaner topical solution) for Dogs and Cats. Fluralaner inhibits the flea’s nervous system by blocking the function of ligand-gated chloride channels (gamma-aminobutyric acid [GABA] receptor and glutamate receptor).5 Unlike most other adulticides, BRAVECTO® Chews protects pets against fleas for 12 weeks, long enough to kill the adult fleas on the pet today, and to kill fleas emerging from existing pupae in the house.5

In clinical trials, BRAVECTO® Topical Solution for Dogs killed almost 100% of adult fleas on dogs for 12 weeks. In addition, common clinical signs of flea allergy dermatitis (erythema, alopecia, papules, scales, crusts, and excoriation) improved as a direct result of eliminating the flea infestations.6

Lufenuron: preventing future infestations

Lufenuron works by inhibiting the formation of chitin, the hard, crunchy material that makes up much of an insect’s shell and the wall of the flea egg. Without chitin to form a healthy eggshell, the flea larvae cannot develop.1,2

Lufenuron circulates in the blood of dogs administered SENTINEL® SPECTRUM® Chews (milbemycin oxime/lufenuron/praziquantel) or SENTINEL® FLAVOR TABS® (milbemycin oxime/lufenuron). Female fleas that ingest blood from a lufenuron-treated dog will deposit the lufenuron in their eggs.2

By interfering with chitin synthesis, polymerization, and deposition, lufenuron prevents most flea eggs from hatching or maturing into adults. In this way, lufenuron prevents and controls flea infestations. It breaks the life cycle of an existing infestation and prevents new populations from becoming established. If the dog picks up an occasional adult flea while out and about, that flea’s eggs will also be unable to hatch.2

Prescribe with confidence

Flea infestations are now both treatable and, more importantly, preventable, with safe and effective products that we can prescribe with confidence. There is no need for another beloved pet to suffer or for owners to use messy, complicated, or old-school products to deal with fleas on their pets and in their homes. To limit flea infestations on pets and prevent flea populations from becoming established in furniture, carpeting, and crevices of the pet’s home, the CAPC recommends that dogs be treated year-round for their entire lives with effective flea control products.4

Don’t send your clients back to the bad old days. BRAVECTO, SENTINEL SPECTRUM Chews, and SENTINEL FLAVOR TABS can be key weapons in your arsenal, fighting back against flea infestations so that pet owners can spend more enjoyable time with their pets. For more information, please see product insert.

Important Safety Information

BRAVECTO Chews for Dogs: The most commonly reported adverse reactions include vomiting, decreased appetite, diarrhea, lethargy, polydipsia, and flatulence. BRAVECTO Topical Solution for Dogs: The most commonly reported adverse reactions include vomiting, hair loss, diarrhea, lethargy, decreased appetite, and moist dermatitis/rash. BRAVECTO Topical Solution for Cats: The most commonly reported adverse reactions include vomiting, itching, diarrhea, hair loss, decreased appetite, lethargy, and scabs/ulcerated lesions. BRAVECTO Topical Solution for Cats is not effective against American dog ticks beyond 8 weeks of dosing.

BRAVECTO has not been shown to be effective for 12-weeks’ duration in puppies or kittens less than 6 months of age. BRAVECTO Chews and Topical Solution for dogs is not effective against the lone star tick beyond 8 weeks of dosing. BRAVECTO Topical Solution for Dogs and Cats are for topical use only. Avoid oral ingestion. The safety of BRAVECTO Topical Solution for Cats has not been established in breeding, pregnant and lactating cats.

All BRAVECTO products contain fluralaner, which is a member of the isoxazoline class. This class has been associated with neurologic adverse reactions including tremors, ataxia, and seizures. Seizures have been reported in dogs receiving isoxazoline class drugs, even in dogs without a history of seizures. Use with caution in dogs with a history of seizures or neurologic disorders. Neurologic adverse reactions have been reported in cats receiving isoxazoline class drugs, even in cats without a history of neurologic disorders. Use with caution in cats with a history of neurologic disorders. See full prescribing information.

SENTINEL® SPECTRUM® Chews (milbemycin oxime/lufenuron/praziquantel). Dogs should be tested for heartworm prior to use. Mild hypersensitivity reactions have been noted in some dogs carrying a high number of circulating microfilariae. Treatment with fewer than 6 monthly doses after the last exposure to mosquitoes may not provide complete heartworm prevention. See full prescribing information. SENTINEL® FLAVOR TABS® (milbemycin oxime/lufenuron). Dogs should be tested for heartworm prior to use. In a small percentage of treated dogs, digestive, neurologic, and skin side effects may occur. See full prescribing information.


  1. PROGRAM® Tablets (lufenuron tablets). Freedom of information summary. Original new animal drug application. Ciba Animal Health, Ciba-Geigy Corporation. November 23, 1994.
  2. SENTINEL® Flavor Tabs® [prescribing information]. Madison, NJ: Merck Animal Health; 2020.
  3. Wright I, Elsheikha H. Flea infestations: epidemiology, treatment and control. The Veterinary Nurse. 2015;5:261-269.
  4. Fleas. Companion Animal Parasite Council website. Updated September 19, 2017. Accessed February 17, 2022.
  5. BRAVECTO® Chews [prescribing information]. Madison, NJ: Merck Animal Health; 2019.
  6. BRAVECTO® fluralaner topical solution Dogs and Cats. Corrected freedom of information summary. Original new animal drug application. Intervet, Inc. July 20, 2016.

About the author

Dr. Keri Shaver meet the team

Keri Shaver

Professional Services Veterinarian
Carolinas Region (NC, SC)