What is milbemycin oxime + afoxolaner?
Milbemycin oxime + afoxolaner (brand name Nexgard Spectra®) is a heartworm disease preventive that also 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.
It is used off label (extra label) to treat other mite infestations in dogs. Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.
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 the medication?
If you miss a dose, give it as soon as you remember, and then wait the recommended time for the next dose, as prescribed by your veterinarian. Do not give the pet two doses at once or give extra doses.
If you are using milbemycin oxime + afoxolaner as a heartworm preventive and more than 8 weeks have passed since the last dose, contact your veterinarian for guidance.
Are there any potential side effects?
Milbemycin oxime + afoxolaner may cause the following side effects:
- Mild vomiting
- Diarrhea
Serious adverse reactions may occur. If any of the following signs develop, stop giving milbemycin oxime + afoxolaner and contact your veterinarian immediately:
- Hyperactivity
- Itching or hives
- Anorexia (no appetite)
- Stumbling or collapse
- Seizures or coma
- Excessive drooling
Are there any risk factors for this medication?
DO NOT USE milbemycin oxime + afoxolaner in:
- Dogs that are heartworm positive or have not recently been tested
- Puppies younger than 8 weeks
- Dogs that are allergic to any component of the drug combination
USE WITH EXTREME CAUTION in:
- Dogs with a history of seizures (afoxolaner belongs to the isoxazoline class of drugs, which have been associated with tremors and seizures)
Some dog breeds (e.g., collies, sheepdogs, and collie or sheepdog-cross breeds) are more sensitive than others to milbemycin oxime + afoxolaner. This sensitivity is typically due to a specific genetic mutation (ABCB1, also known as MDR1) that makes them less able to tolerate high doses of certain medications. Doses used for heartworm prevention in milbemycin oxime + afoxolaner are safe to use in these breeds of dogs.
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?
Several drugs can interact with milbemycin oxime + afoxolaner, including:
- Amiodarone
- Azole antifungals
- Cyclosporine (Atopica®)
- Diltiazem
- Erythromycin
Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.
Is any monitoring needed with this medication?
- Your dog should be tested for heartworm before receiving any product containing milbemycin oxime. A life-threatening reaction can occur if your pet has a high load of immature worms and is given milbemycin.
- For dogs with potential milbemycin sensitivity, DNA screening may be done before receiving the medication to determine if your dog has the genetic mutation responsible for adverse reactions to milbemycin oxime.
- Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
- At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.
How do I store this medication?
- Store milbemycin oxime + afoxolaner at room temperature (59°F to 86°F or 15°C to 30°C).
- Store in a dry location, away from heat and direct sunlight. Keep the blister pack inside the original box to protect it from light.
- Keep the container out of reach of children and pets. 
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. Be prepared to provide information about the product and your pet's weight and symptoms.
