Pet Medication 101: Milbemycin Oxime

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Pet Medication 101: Milbemycin Oxime

It’s important to understand a medication’s uses and side effects before giving it to your pet. This medication info sheet is meant to give you a good understanding of what milbemycin oxime (Interceptor) is used for, how it works, and potential side effects in cats and dogs. Always consult a veterinarian before giving your pet any medication.

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1. Drug Name:

milbemycin oxime

2. Brand Names:

Interceptor, Milbemite

Combined with other antiparasitic ingredients in Trifexis, Sentinel, Milbemax, Milbeguard

3. How Dispensed:


4. Forms:

2.3mg, 5.75mg, 11.5mg, and 23mg tablets; 0.1% otic solution

5. Drug Type/Class:


6. Uses in Dogs and Cats:

Heartworms, hookworms, roundworms, whipworms, ear mites, sarcoptic mange, and demodectic mange

7. How it Works:

Milbemycin binds to chloride channels in the nerve and muscle cells of parasites, which forces them to stay open, causing paralysis of the affected tissue and killing the parasite.

8. Side Effects and/or Signs of Overdose:

Dilated pupils, drooling, incoordination, weakness, fever, seizures, coma, and death, especially in dogs with an MDR1 mutation

MDR1 mutation: Collies, Shetland Sheepdogs, Australian Shepherds, Old English Sheepdogs, merle-colored Pomeranians, and long-haired Whippets often have a mutation in the gene that makes P-glycoprotein. This mutation allows milbemycin to cross the blood-brain barrier and can result in life-threatening complications. Normal heartworm preventatives do not use high enough doses for this to become a problem, but if a higher dose of milbemycin is being used, a commercial test kit should be used to determine if a dog has this particular mutation.

9. Drug Interactions:

Cyclosporine, Ketoconazole, Itraconazole, Fluconazole, Erythromycin, Spironolactone, Amiodarone, and Diltiazem

10. Cautionary Statements:

  • Animals should be heartworm tested before receiving any product containing milbemycin.
  • If milbemycin is given to a heartworm-positive dog that has circulating microfilaria, the larval heartworms may die abruptly, resulting in anaphylactic shock.
  • Use with extreme caution is Collies and Collie-related breeds, especially at higher doses (see MDR1 mutation notes above).
  • Not approved for use during pregnancy and lactation.
  • Not recommended for use in puppies less than 4 weeks of age or kittens less than 6 weeks of age.
  • Not for use in animals weighing less than 2 pounds.
  • Although milbemycin side effects usually resolve after a few days, side effects may persist longer in patients with liver or kidney disease.

Read more:

Heartworm Disease in Dogs and Cats

Roundworms in Dogs and Cats

Hookworms in Dog and Cats

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