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Trifexis for Dogs

By | Last Updated: 23rd February 2023

What is Trifexis for dogs

Trifexis is an anti-parasitic medicine used for preventing heartworm disease, protecting against flea infestations, and controlling roundworm, whipworm, and hookworm infections [1]. Available as beef-flavored tablets, Trifexis may be used to manage multiple parasitic infections in dogs, including Angiostrongylus vasorum, Ancylostoma caninum, Toxocara canis, Toxascaris leonina, and Trichuris vulpis [2, 3].

Can dogs safely take Trifexis

The medicine is approved for use only in dogs [1] and may be prescribed as per the benefit-risk assessment of a vet [3]. Studies have shown its safety and efficacy in treating intestinal nematode infections, and in preventing flea infestations in dogs [4].

Although there are some cases of deaths claimed to be linked with Trifexis, there is no scientific evidence yet to prove it [7]. Make sure to discuss with the vet about all the potential effects.

Quick Information

Trifexis for Dogs

Generic name (Active ingredients): Spinosad, milbemycin oxime [2, 5]

Brand name: Trifexis® [5]

Type: Heartworm preventive and flea control [1]

FDA approved: Only for dogs [1]

Availability: Only on prescription [1]

Who can take it: Dogs [1]

Available forms: Tablets [1, 2]

How does Trifexis work

Spinosad, one of the primary ingredients of Trifexis, interferes with the normal functioning of the nervous system receptors in the fleas [7]. When the insect comes into contact with spinosad, it causes tremors and muscle contractions due to hyperexcitation of motor neurons, eventually resulting in its paralysis and death [5].

Milbemycin oxime, on the other hand, binds to GluCls (glutamate-gated chloride ion channels) in the muscle and nerve cells of the fleas, thereby increasing the flow of chloride ions through the cell membrane, resulting in paralysis and death of the parasite due to hyperpolarization of the cell [5]. It may help in disrupting the way neurotransmitters are passed between the nerve cells in internal worm’s body [5, 7].

Sometimes, you may still notice fleas on your dogs after giving the medication. In most cases, it is likely that your dog has been exposed to some new fleas, which are then killed and prevented from laying eggs when the treatment is continued [7].

Trifexis dosage: how much and how often to give it to your dog

Follow your vet’s dosage recommendations carefully. The typically prescribed dose is a combination of 13.5mg/lb spinosad and 0.2mg/lb milbemycin oxime, given orally with food once a month [5]. Consult your vet regarding whether or not to crush the pills, as there is a lack of studies to show any difference in the effectiveness of the drug when crushed [10].

Preventing heartworm disease usually involves administration of one tablet per month, for 3 months since the time when your dog was bitten by the carrier mosquitoes [5].

In case of a missed dose, administer the tablet as soon as you remember, and then resume the monthly dosing schedule for lessening the chances of adult heartworm development and flea re-infestation [2, 5].

Possible side effects

Mild vomiting within the first 48 hours of dosage was found to be common [7, 9]; however, no acute or prolonged vomiting was reported during research studies carried out on dogs administered with Trifexis [5, 8]. Other possible side effects may include:

  • Lethargy [1]
  • Decreased appetite [1, 8]
  • Diarrhea (urgency to defecate, watery stools, flatulence) [8]
  • Skin irritation (scratching, itching, or redness) [1]
  • Incoordination (trembling, shaking, stepping oddly) [8]

A Trifexis overdose may lead to [1]:

  • Drooling (excessive salivation)
  • Decreased activity
  • Excessive barking or vocalization
  • Coughing

If you see any of the above signs, contact your vet immediately [1].

When not to give Trifexis to your dog

Inform your veterinarian about any health issues your dog may have had. Trifexis should be cautiously used if your dog has epilepsy, MDR-1 gene mutation, or is pregnant/nursing [3]. For avoiding a possible contraindication, the medicine is usually not given to dogs that are:

  • Less than 14 weeks old [3]
  • Hypersensitive to any of the ingredients [3]
  • Under 8.6 lbs (3.9 kg) in weight [3]

Although Trifexis is not known to cause any drug interactions, you should inform the vet if your dog is being administered with any other medications [1].


    1. Spinosad plus Milbemycin oxime – Petmd.com
    2. Trifexis – 1800petmeds.com
    3. Trifexis, spinosad/milbemycin oxime Summary of Product Characteristics – Ema.europa.eu
    4. CVMP assessment report for Trifexis (EMEA/V/C/002635/0000) – Ema.europa.eu
    5. Trifexis – Drugs.com
    6. TRIFEXIS – spinosad and milbemycin oxime tablet, chewable – Dailymed.nlm.nih.gov
    7. Trifexis Spinosad/milbemycin oxime – Ema.europa.eu
    8. Trifexis Side Effects – Trifexis.com
    9. Trifexis For Dogs: Uses, Dosage, & Side Effects – Dogtime.com
    10. FAQ Using Trifexis – Trifexis.com
    11. Compare Comfortis to Sentinel to Trifexis – 1800petmeds.com

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