Milbemycin for Dogs and Cats

Medically Reviewed by Joshua Conrad, PharmD on October 09, 2024
Written by Kathleen Claussen, DVM
4 min read

Milbemycin (Interceptor, Milbeguard, Milbemite, Milbehart) is a medicine used to prevent heartworms and to control some intestinal parasites in dogs and cats.  

In dogs, milbemycin is approved for control of hookworms in the intestines and control and removal of adult roundworms and whipworms in the intestines.  Dogs must be at least 4 weeks old and at least 2 pounds (0.9 kilograms) to get milbemycin.  

In cats, milbemycin is approved for removal of adult hookworms and roundworms in the intestines. Cats must be at least 6 weeks old and weigh at least 1.5 pounds (0.7 kilograms) to get milbemycin.

Milbemycin is classified as a macrolide antiparasitic for monthly prevention of heartworms and control of some intestinal parasites in dogs and cats. Milbemycin can be prescribed “extra-label” or “off-label,” such as in dogs for some skin mites (demodectic and sarcoptic mange).  “Extra-label” or “off-label” means that there is evidence of safe and effective use but the FDA has not approved that use.

Milbemycin is FDA-approved for use in dogs, puppies, cats, and kittens. It is generally well tolerated in animals. 

Milbemycin is available by prescription from your veterinarian or from a veterinary pharmacy. It is available as a beef-flavored chewable tablet in various sizes. Milbemycin is available as a single-ingredient medicine or in combination products.

Milbemycin can be given with or without a small amount of food. Make sure the entire chewable tablet is eaten. Give milbemycin every 30 days (monthly) without stopping for best results.

Always follow your veterinarian’s directions for giving medicines to animals. Tell your veterinarian about any medicines, vitamins, supplements, or herbal therapies that you are giving your pet. Talk to your veterinarian before stopping any pet medicines.  

  • Milbemycin is well tolerated by animals including puppies and kittens.
  • Milbemycin is FDA-approved for use in dogs, puppies, cats and kittens.
  • You only have to give one chewable tablet every 30 days.

You and your veterinarian should monitor your pet for improvement of their condition, as well as for side effects of the medicine. If milbemycin is used for mites, follow-up skin tests may be done by your veterinarian. If milbemycin is used for intestinal parasites, follow-up fecal (stool) tests may be checked.

Before giving milbemycin to dogs, a heartworm test must be negative. The heartworm test should be repeated yearly or if there are missed doses of milbemycin. Speak to your veterinarian before starting your cat on milbemycin since heartworm testing can be unreliable in cats.

Do not use milbemycin in animals that are allergic to it.  Do not use milbemycin in dogs that weigh less than 2 pounds or are less than 4 weeks old. Do not use milbemycin in cats that weigh less than 1.5 pounds or are less than 6 weeks old. Do not use in dogs diagnosed with heartworm disease. Use with caution in animals that have a history of seizures (epilepsy). Do not use milbemycin in breeding, pregnant, or nursing cats. Use milbemycin with caution in breeding, pregnant, or nursing dogs. 

Milbemycin is usually well-tolerated in animals.  Side effects in dogs include:

  • Vomiting
  • Diarrhea or loose stool
  • Decreased appetite
  • Depression
  • Tiredness or fatigue

Side effects have not been formally studied in cats but may be similar to those in dogs.

While there is a low risk of serious side effects with milbemycin, they can happen. Serious side effects include:

  • Seizures or tremors 
  • Weakness
  • Difficulty walking

If you suspect that your pet is having a serious side effect or may have been overdosed, call your veterinary clinic immediately. If it is outside of regular office hours, you may contact a local emergency veterinary hospital or an animal poison control center. 

You can reach the ASPCA Animal Poison Control Center at 888-426-4435 or the Pet Poison Helpline at 855-764-7661.

Using multiple medicines can sometimes change how your pet’s medicines work or increase your pet’s risk for serious side effects. Always tell your veterinarian about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements that your pet is using.

Some medicines that may interact with milbemycin are benzodiazepines such as alprazolam (Xanax) or diazepam (Valium), “azole” antifungals such as itraconazole or ketoconazole, cyclosporine, diltiazem, and erythromycin.  

This may not be a complete list of medicines that can interact with milbemycin.  Always check with your veterinarian.

  • Keep milbemycin out of reach of children.
  • Wash your hands after giving milbemycin to your pet.
  • Do not handle milbemycin if you are allergic to it.

Milbemycin is well tolerated by animals and the risk of an overdose is low. If you are concerned your pet is having an adverse reaction or if you suspect your pet has taken more milbemycin than prescribed, call your veterinarian or veterinary emergency clinic immediately.

If your missed a dose, give the dose when you remember and then continue with the rest of the medicine at the correct dosing schedule. Do not double the dose of the medicine.  

If more than 8 weeks have passed since the last dose, start the monthly milbemycin again. Your dog will need to have a heartworm test performed in 6 months to determine if there is heartworm disease. It takes 6 months from the bite of an infected mosquito until a dog may test positive for heartworm disease.

Store milbemycin in the original packaging at room temperature. Protect it from light.