Milbemycin & Spinosad (Trifexis®, ComboGuard®) for Dogs

Milbemycin & Spinosad (Trifexis®, ComboGuard®) for Dogs

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of Milbemycin & Spinosad for Canines

  • Trifexis® is one of the most commonly used flea, heartworm and worm treatment/prevention medication used in dogs. Trifexis contains a combination of two drugs including milbemycin & spinosad. Trifexis comes as a chewable pill in weight-dependent sizes. Below is some detailed information about the two drugs that make up Trifexis, Milbemycin & Spinosad.
  • Milbemycin acts by disrupting nerve transmission within the parasite leading to death of the parasite.
  • Spinosad™ is a drug that provides flea control for dogs. It contains antiparasiticagents used to kill and prevent fleas. Spinosad is a member of the spinosyns class of insecticides. The effects of Spinosad™ last about 30 days against fleas. It is documented to begin killing fleas within 30 minutes with 100% effectiveness within 4 hours.
  • Parasitic infections are common in dogs and cats and include external parasites (fleas, ticks, mites), and internal parasites (intestinal worms, lungworms and heartworms).
  • Trifexis® is a Prescription drugand can only be obtained from a veterinarian or by prescription from a veterinarian.

Brand Names and Other Names
of Milbemycin & Spinosad

  • This drug is Registered for use in animals only.
  • Human formulations: None
  • Veterinary formulations: Trifexis®, ComboGuard®,

Uses of Milbemycin & Spinosad
for Dogs

  • Trifexis® is used in the control and treatment of adult flea infestations, control of hookworm, roundworm, and certain whipworm infections and as a highly effective preventative of heartworm disease.
  • Trifexis® contains milbemycin which is a potent **microfilariacidal** drug, meaning it can kill the microscopic offspring of heartworms. Microfilaria circulate in the blood of infected dogs and are typically treated after killing the adult heartworm parasite with another drug (melarsamine). Milbemycin is one of the drugs veterinarians use to kill the microfilaria as there are no drugs approved for this use by the FDA.
  • For more information on flea infestations, please see Flea Infestation in Dogs and Flea Allergy Dermatitis.

Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, Trifexis® can cause side effects in some animals.
  • Trifexis® should not be used in animals with known hypersensitivity or allergy| to the drug.
  • Trifexis® should not be given to dogs with allergies to soy or pork as the pill is flavored.
  • Animals should be tested for heartworm infection before beginning prevention with Trifexis.
  • Trifexis® is approved for use in dogs and puppies over 8 weeks of age and 5 pounds of body weight or greater. It should be used with caution in breeding females. Milbemycin has been found safe in collie breeds and in collie mixed breeds.
  • Trifexis® may interact with other medications. Consult with your veterinarian to discuss using other medications when your pet is on Spinosad™. One interaction of note is when used with high doses of ivermectin – have resulted in signs of ivermectin toxicity in some dogs.
  • Trifexis® is an oral agent. The most common side effect noted was vomiting. Other adverse reactions included decreased appetite, inflammation or redness of the skin, redness of the ears and/or diarrhea. Documented reactions are general mild.

How Milbemycin & Spinosad is Supplied

Trifexis® is available as an oral chewable tablet. Trifexis® can be given to dogs and puppies 8 weeks or older. It is dosed by body weight. Minimum weight for Trifexis® is 5 lb. Available sizes include:

  • 5 to 10 pounds – 140 mg tablet
  • 10.1 to 20 pounds – 270 mg tablet
  • 20.1 to 40 pounds – 560 mg tablet
  • 40.1 to 60 pounds – 810 mg tablet
  • 60.1 to 120 pounds – 1620 mg tablet
  • Dogs over 120 pounds should be given the appropriate combination of tablets.

Dosing Information of Milbemycin & Spinosad for Dogs

  • Medication should never be administered without first consulting your veterinarian.
  • The dose of Trifexis® is based on weight and administered every 4 weeks throughout the flea season.
  • Treatment can begin any time of year but should ideally begin 1 month prior to flea season.
  • Trifexis® should be administered with food to maximize effectiveness.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. The manufacturer suggests monthly treatments to protect against flea re-infestation. Be certain to complete the prescription unless specifically directed by your veterinarian.

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