My dog is on Trifexis and still has fleas

Dogs can be treated with oral medications that can defend dogs for up to 30 days from worms and fleas, as is the case with triplex, but what can be happening when this type of medication is used, and fleas can still be observed on the animal? To answer this question, this post will talk about parasite resistance to drugs and the main reasons for drug failure.

My dog is on Trifexis and still has fleas

Trifexis is a drug that can kill fleas and provide protection to the dog for at least a month against fleas and intestinal parasites that fleas can cause in dogs. Failure to use the medication can result in the persistence of fleas in the environment and on the animal.

Several causes may be related to the persistence of fleas in dogs with the same treatment. One of them is the suspicion of resistance to the active principle responsible for killing the flea.

Products that are used constantly can predispose your target’s resistance. Resistance happens when certain fleas create biological mechanisms to not be affected by the drug. So these fleas become resistant and pass the genes on to the next generations that will also be resistant.

The veterinarian should be consulted when observing that fleas remain on dogs even if the treatment is done properly. So the vet will do tests on the fleas to test which drugs they are not resistant to, making it possible to treat the animal.

Another factor that can interfere in the treatment of dogs for fleas is the inappropriate use of medicines. The triflex must be given to the dog along with the food.

And the treatment of the dog must always be associated with cleaning and disinfection of the environment in which the animal stays.

About fleas in dogs

Fleas can bring many harms to dogs, among them we will talk:

  • Dog stress and wounds;
  • Canine dermatitis;
  • Allergic dermatitis to flea bites;
  • Worms.

Dog stress and wounds

When fleas walk on the dog’s back, they can cause the animals to scratch themselves, so excessive itching can cause the dogs to end up injuring themselves from scratching too much. These wounds can be treated, but if the animal continues to have fleas, it will continue to scratch.

The stress caused by excessive itching can lead to a change in the dog’s behavior in addition to leading to a reduction in the dog’s immunity, thus favoring the appearance of other diseases and even opportunistic diseases.

Canine dermatitis

The skin is the body’s natural barrier that is in balance with its typical microbiota. When any type of stress alters the integrity of this tissue, it can lead to the proliferation of scabies, bacteria and even fungi resulting in dermatitis.

Stress to the skin caused by the itching of the dog with fleas or by the lesion generated at the site of the flea bite can be predisposing factors for the appearance of dermatitis. Beside fleas the skin is injured, thus altering the integrity and local immunity.

Dermatitis must be treated according to the specific parasite causing the disease, and therefore a veterinarian must be consulted. However, if the animal continues to present fleas, it will probably present all the dermatitis again. Therefore, treatment of both dermatitis and fleas is necessary.

Allergic flea bite dermatitis

Some dogs are allergic to flea drools. When the flea is feeding on the dog it releases anticoagulant and anesthetic secretions. This drool can lead to a generalized reaction in the dog that has an allergy. So, dogs can have alopecia and itching in various regions of the body.

Flea bite dermatitis is treated with oral and even topical anti-allergy medications. In addition, all fleas from animals and the environment must be eliminated. Currently, there are repellent collars, topical repellents and periodic medications that can prevent flea contact and infestation in dogs.


Some fleas can carry a worm called Dipylidium caninum. This worm is transmitted when the flea feeds on the dog’s blood. Dipylidium travels through the bloodstream and lodges in the gastrointestinal tract.

This worm when left untreated can lead to abdominal discomfort and perianal itching that results in the dog dragging its butt on the floor to scratch. In addition, this worm associated with a flea infestation can cause dogs to have anemia.

Treatment involves getting rid of fleas from the animal and the environment, and worm remedies can also be used. Animals with contaminated fleas can transmit to other healthy animals, so contact with other dogs should be avoided if the animal has fleas.

Treatments for fleas in dogs

Fleas can be eliminated by drugs that can be ingested, such as drugs that kill fleas due to the concentration of the drug in the dog’s blood. So, when ingesting the blood with the medicine the fleas end up dying. Usually, these medications can stay in the dog’s circulation for 30 and even 90 days, thus protecting the animal from new infections.

Spray medicines, powders, shampoos, and creams can also be used. This type of repellent should be used with caution because many of them can lead to dog intoxication when ingested by the animal. 

Some of these products can protect the animal for a few days, while others will take effect immediately and after washing the dog’s hair, the medicine loses its effectiveness, leaving the animal predisposed to new infections.

In addition, there are repellent collars on the market today, these collars can help repel ticks, fleas and even some flies. Repellent collars can have a longer effect, from 4 to 6 months. They are excellent ways to prevent dogs from coming into contact with fleas.

The environment must also be treated as most of the flea cycle takes place there. Therefore, chemical products can be used to kill fleas. In addition, it is important to wash the dogs beds, towels, bedspreads and sheets on which the animal is used to lying down. In this way, flea control can be done avoiding the dog’s infestation.


Flea treatment must be done thoroughly. The treatment to be effective must associate the treatment of the animal with that of the environment. You should always remember that the medication must be used correctly and be repeated at the frequency indicated by the manufacturer. Even so, if the animal continues to have fleas, the veterinarian should be consulted.

Frequently Asked Questions (FAQs): My dog is on Trifexis and still has fleas

How do animals catch fleas?

Dogs can get fleas when they come into contact with other infected animals, environments or objects. Dogs can usually acquire fleas on walks or places with a lot of dog crowds.

What makes fleas appear?

Fleas can appear on infected animals or even humans as these insects can stick to a visitor’s clothing or skin. Dogs can be contaminated on the streets, in day care, hotels and even in veterinary clinics.

Where do fleas live in the environment?

You’ll find them anywhere and everywhere the dog frequents such as on blankets, beds, carriers, sofas, chairs, carpet, cracks or crevices in the floor and corners.


Fernandes, F. B. (2014). Controle de Ctenocephalides spp. em cães com dermatite alérgica à picada de pulga.

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