Collie Ivermectin Sensitivity Symptoms

Many collies carry a gene causing ivermectin sensitivity.
i collie image by Ivonne Wierink from

Just a simple cheek swab test can determine if your collie is sensitive to ivermectin. An effective drug for canine heartworm prevention, ivermectin is not suitable for administration to pure or mixed-breed collies carrying a genetic mutation that doesn't allow ivermectin and certain other medications to properly cross the blood/brain barrier.


Effective against many kinds of worms and given to many species, including horses and cattle, ivermectin came onto the market in the 1980s. It also kills mites and lice but does not affect tapeworms. It kills larval heartworms -- microfilariae -- but not adult heartworms. While some veterinary professionals contend that low-dose canine ivermectin should not harm collies, you should discuss the matter with your vet if your collie tests positive for the mutant gene.

Mutant Gene

Some collies carry a mutant gene for the protein P-glycoprotein, which keeps drugs out of certain parts of the body. The mutant gene fails to keep drugs like ivermectin out of the collie's central nervous system. The symptoms experienced by affected collies result from ivermectin gaining access to the central nervous system. Approximately 35 percent of collies carry the gene and are seriously affected if exposed, while 45 percent carry the gene but do not suffer any effects or symptoms are mild. Approximately 20 percent of collies do not carry the gene. These percentages are the same for dogs with only one collie parent, and for various types of collies, including border collies.


In the United States, heartworm medication is available only by prescription -- this allows your vet to check for a heartworm presence, as affected dogs shouldn't receive the medication. Your vet will not prescribe heartworm medication to a dog with obvious collie heritage without performing the genetic test. According to the Washington State University School of Veterinary Medicine, symptoms of ivermectin toxicity in collies include blindness, breathing difficulties, extreme salivation, coma, loss of coordination and death.


While you obviously don't want your collie to experience ivermectin sensitivity, you don't want him susceptible to heartworms, either. Heartworm infestation can also kill a dog. If your dog tests positive for the gene mutation, you can protect him from heartworms with Interceptor, Novartis Animal Health's medication containing milbemycin oxime. This oral heartworm preventative is given once a month.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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