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Trifexis for Dogs: Heartworm, Parasite & Flea Medicine 

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Medication details

  • Medication type: Antiparasitic
  • Form: Tablet
  • Prescription required? Yes
  • FDA approved? Yes
  • Brand names: Trifexis
  • Available dosages: 5-10lbs: (140 mg spinosad and 2.3 mg milbemycin oxime); 10.1-20 lbs: (270 mg spinosad and 4.5 mg milbemycin oxime); 20.1-40 lbs: (560 mg spinosad and 9.3 mg milbemycin oxime); 40.1-60 lbs: (810 mg spinosad and 13.5 mg milbemycin oxime); 60.1-120 lbs: (1620 mg spinosad and 27 mg milbemycin oxime)
  • Expiration range: Varies; refer to package label for specific expiration dates

Parasite protection is an important part of preventative care in veterinary medicine. Various products are available to kill fleas and ticks, prevent heartworm disease, and treat and control intestinal parasite infections. 

In the United States, 34 percent of dogs are infected by intestinal parasites, such as roundworms and hookworms. For dogs in the southeastern U.S., this percentage is even higher [1]. Some internal parasites are zoonotic, which means they can make people sick too. External parasites like fleas and ticks are also very common in dogs and can transmit infectious diseases to pets and people.

Monthly parasite control products, such as Trifexis, can help protect your dog and your household against parasitic risks. Let’s take a closer look at what Trifexis for dogs is and how it works.

What Is Trifexis for Dogs?

Trifexis for Dogs packaging

Trifexis is an antiparasitic product for dogs that is used to protect against fleas, heartworm disease, hookworm, roundworm, and whipworm. It is a chewable tablet given by mouth, so it is typically easy to administer and well-liked by dogs. Trifexis is manufactured by Elanco and contains the active ingredients spinosad and milbemycin oxime. It was approved by the FDA on Jan. 4, 2011 [4]. It is not currently available in a generic form and is only available by prescription from your primary care veterinarian. It is readily available throughout the United States.

What Does Trifexis for Dogs Look Like?

Trifexis is a light brown, circular tablet. It comes in boxes of 1, 3, or 6 tablets that are each color-coded according to the dosage and intended weight category. 

What Is Trifexis Used for in Dogs?

Veterinarians typically prescribe Trifexis to protect against parasitic infections in dogs. These include fleas, heartworm, hookworm, roundworm, and whipworm in dogs. Trifexis is not effective against ticks.

Protection against heartworms is important to keep your dog’s heart and lungs healthy. If your dog gets heartworm disease, they will need to undergo expensive treatments and have activity restrictions until the heartworms have been eliminated. 

Likewise, intestinal parasites can be especially bothersome to dogs. They can result in poor appetite, weight loss, diarrhea, bloody stools, and vomiting. Once infected, it can take some time to fully eliminate these parasites from the dog and their environment. Another concerning factor is that two intestinal parasites—hookworms and roundworms—are zoonotic, which means they can be spread from animals to humans. Hookworm infections in people can cause a skin condition called cutaneous larva migrans, while roundworm infections in people can cause visceral larva migrans, which affects internal organs. Reducing the risk of zoonotic infection is just one important reason to keep your dog on monthly parasite protection. 

How Does Trifexis Work?

Spinosad is an active ingredient in Trifexis that is used to kill fleas and prevent infestations. It works by activating certain receptors in the fleas, resulting in involuntary muscle tremors. Continued activation of these receptors leads to paralysis followed by death.

Milbemycin oxime is the component of Trifexis responsible for preventing heartworm disease and treating and controlling adult hookworm, roundworm, and whipworm infections. It works by binding to certain channels in nerves and muscle cells, which allows chloride to get into these cells. Too much chloride leads to paralysis and death of the parasites. Milbemycin oxime can also disrupt transmission of certain neurotransmitters within the parasite, which has a detrimental effect [3]. 

How to Give Trifexis to Dogs

Trifexis is administered orally to dogs once a month. It is recommended for pet parents to give this medication on the same day each month to ensure continuous protection. Most dogs are happy to take this medication since it is beef-flavored and viewed as a treat. However, for dogs who may not readily take it, pet parents can put it in a pill pocket or a “meatball” of wet dog food to disguise it. If your dog still won’t take the medication, contact your veterinarian who can demonstrate safe, alternative ways to administer it. 

Trifexis Reviews

Trifexis is well-accepted in the veterinary community. I have used Trifexis in my own dogs before, and it was well-tolerated. I prefer oral medications over topical ones simply because they are less messy and don’t leave residue in the dog’s fur. Trifexis is also beef-flavored, so in my experience the tablets are also easily administered, much like a treat. 

Dogs who would benefit from this product include those who spend most of their time indoors and tend to stay in their own yards. This would not be a good option for dogs who regularly hike or spend a lot of time in wooded areas since it has no protection against ticks. 

With all of the options for parasite protection, it can easily become overwhelming. However, pet parents can work with their veterinarians to discuss the option that would be the best fit for their pet. 

There are several things to consider when choosing a product. Many pet parents are curious about how Trifexis compares to other parasite protection products on the market. Trifexis is a good alternative to Comfortis, which only treats fleas, because it has the added benefit of protecting against heartworm disease and three intestinal parasites (hookworm, roundworm, and whipworm). However, Comfortis Plus and Trifexis provide the same protection. While Nexgard and Bravecto protect against both fleas and ticks, they unfortunately provide no protection against intestinal parasites or heartworm disease like Trifexis does. Bravecto is available as a chew or a topical solution and only needs to be administered once every three months, while Trifexis must be administered once monthly. 

Simparica Trio is a combination parasite control product that protects against both fleas and ticks, heartworm disease, roundworms, and hookworms. However, it does not protect against whipworm infections like Trifexis.

Trifexis Side Effects

While Trifexis is generally well-tolerated in most dogs, there are some side effects to be aware of. When administering this product, pet parents should watch for any abnormal behaviors in their dogs that could signify a reaction. The following side effects may occur when using Trifexis [2]:

  • Vomiting 
  • Diarrhea
  • Reduced appetite
  • Itching
  • Lethargy

Trifexis should not be taken with other medications formulated to prevent fleas or heartworm disease. Serious side effects may occur if high doses of ivermectin are used concurrently with Trifexis [2]. Always discuss any medications your pet is taking with your veterinarian prior to starting your dog on Trifexis. This will help prevent drug interactions and ensure safety.

Trifexis Dosage for Dogs

The dosage of Trifexis is based on a dog’s weight. It is safe for use in puppies who are 8 weeks of age or older and at least 5 pounds [2]. It should be given once monthly for optimal protection. There are five dosage forms available to cover the following weight ranges: 

  • 5-10 lbs
  • 10.1-20 lbs
  • 20.1-40 lbs
  • 40.1-60 lbs
  • 60.1-120 lbs

What Does Trifexis Cost?

Trifexis is an affordable option for parasite protection. While there is a monthly cost, protection is much less expensive than the treatment that would be required if your dog developed a severe infestation or disease. Pet parents can expect to pay around $20 a month for this product, though the price will vary slightly based on the strength of the dose (which depends on your dog’s size).

Trifexis Storage Instructions

This product should be stored at room temperature. 

Where to Buy Trifexis

Interested in purchasing Trifexis for dogs? Check to see if this medication is available on your veterinarian’s online pharmacy.


  1. Kansas State University Veterinary Health Center. (n.d.). Zoonotic Potential of Common Cat/Dog Intestinal Parasites. Retrieved from https://www.ksvhc.org/services/pet-health-center/intestinal-parasites.html 
  2. https://pet.elanco.com/us/en/trifexis/dose-administration-safety
  3. https://www.elancolabels.com/us/trifexis
  4. https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/878