Milbemycin Oxime + Afoxolaner

What is milbemycin oxime + afoxolaner?

Milbemycin oxime + Afoxolaner (brand name Nexgard Spectra®) is a Canadian heartworm disease preventive and treats intestinal parasites (e.g., hookworms, roundworms, and whipworms), kills fleas and ticks (American dog tick, black-legged tick, and lone star tick), treats demodicosis caused by Demodex mites, and reduces Lyme disease infections in dogs.

Milbemycin oxime + ALfoxolaner is also used ‘off-label’ to treat other mite infestations in dogs. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.

How is milbemycin oxime + afoxolaner given?

Milbemycin oxime + afoxolaner is given by mouth as a flavored chew tablet. It can be given with or without food, but if your pet acts sick or vomits after getting the tablet on an empty stomach, try giving the next dose with a small amount of food.

This medication should take effect within two days for intestinal parasites and within 24 hours for external parasites. Improvements in clinical signs should follow.

What if I miss giving my pet a dose?

Give the missed dose as soon as you remember and then wait the amount of time between doses recommended by your veterinarian before giving the next dose. Do not give your dog two doses at once or give extra doses. If you are using milbemycin oxime + afoxolaner as a heartworm preventive and more than eight weeks have passed since the last dose, contact your veterinarian for guidance.

Are there any potential side effects?

At prescribed doses, milbemycin oxime + afoxolaner is well-tolerated. Rarely, mild vomiting or diarrhea may occur. Contact your veterinarian immediately if you observe hyperactivity, itching or hives, anorexia (no appetite), stumbling or collapse, seizures or coma, or excessive drooling.

Are there any risk factors for this medication?

Milbemycin oxime + afoxolaner is safe for use in most dogs. However, it should not be used in dogs that are heartworm positive or have not recently been tested, puppies younger than eight weeks, or dogs that are allergic to any component of the drug combination.

Afoxolaner belongs to the isoxazoline class of drugs, which have been associated with tremors and seizures. Milbemycin oxime + afoxolaner should be used with caution in dogs with a history of seizures.

Some dog breeds (e.g., collies, sheepdogs, and collie or sheepdog-cross breeds) are more sensitive to milbemycin than others. This is typically due to a specific genetic mutation (MDR1) that makes them less able to tolerate high doses of milbemycin. Doses used for heartworm prevention in milbemycin oxime + afoxolaner are safe to use in these breeds of dogs (see the handout “Multidrug Resistance Mutation MDR1” for more information). Your veterinarian will advise you on the safety of milbemycin oxime + afoxolaner use in your dog.

Are there any drug interactions I should be aware of?

Other drugs can interact with milbemycin oxime, including cyclosporine (Atopica®), amiodarone, diltiazem, azole antifungals, and erythromycin. No interactions with afoxolaner have been documented. Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Your dog should be tested for heartworm before receiving any product containing milbemycin oxime. If your pet has a high load of immature worms and is given milbemycin oxime, a life-threatening reaction can occur.

For dog breeds with potential milbemycin oxime sensitivity, screening may be done ahead of receiving the medication. DNA testing can determine if your dog has the genetic mutation responsible for adverse reactions to milbemycin oxime.

How do I store milbemycin oxime + afoxolaner?

Store milbemycin oxime + afoxolaner at room temperature (59-86°F, 15-30°C), in a dry place away from heat and direct sunlight. Keep the blister pack inside the original box to protect it from light.

What should I do in case of an emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.