Ivermectin Sensitivity

Ivermectin (Heartgard/Heartgard Plus, Iverhart/Iverhart Plus, Tri-Heart Plus)

"In 2001, a group led by Dr. Katrina Mealey at Washington State University identified the mutation underlying adverse drug response in Collies (including so-called ivermectin sensitivity). Shortly thereafter, the researchers found the mutation in an Australian Shepherd, suggesting that other related breeds might be predisposed to multiple drug sensitivities. This prediction agreed with anecdotal observations that several other breeds also appeared to be supersensitive to the drug ivermectin." Read the entire article.

"For many years, veterinarians knew a certain pharmaceutical used to eliminate internal parasites in animals was very toxic to a subpopulation of collies. What they didn’t know was why. Now a pharmacologist at the WSU College of Veterinary Medicine has discovered a mutant gene for a key transport protein in the susceptible collies. The gene codes for P-glycoprotein, a large protein complex that acts to pump medications out of the brain and back to the bloodstream where they can be metabolized safely. In the collies that lacked the complete gene for P-glycoprotein, they do not produce the complete protein and cannot pump out the medications". Read the entire article.

"Collie owners have long known that ivermectin in the treatment of helminths and mites can result in death of some Collies. Until the mutation and its frequency were discovered, the inconsistency in toxic reaction within the breed caused some confusion. Now we know that approximately 30% of collies are homozygous for the mutation, and these are the Collies particularly at risk. Because a commercial test is now available, purebred Collies should be genetically tested before administering any drug that is a P-glycoprotein substrate in high doses." Additional information at the American Working Collie Association

Pharmacogenetics: It’s not just about ivermectin in collies -- Patricia Dowling, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan S7N 5B4 -- "When considering the use of macrocyclic lactones such as ivermectin or moxidectin in dogs, veterinarians have followed the adage, “white feet, don’t treat.” This refers to the known sensitivity of Scotch collies (both rough and smooth) to neurotoxicity when administered these drugs at higher than label doses. But the adage has also been applied to many other herding breeds and has prevented veterinarians from using these drugs in situations where they would have been ideal." Read the entire article.


Breeds that are known to carry the mdr1 mutation include Australian Shepherds, Collies, English Shepherds, Longhaired Whippets, McNabs, Old English Sheepdogs, Shetland Sheepdogs, white German Shepherds and Silken Windhounds. Research has shown that three out of four Collies have at least one copy of the mutated gene. This means that if your dog is mixed with any of these breeds, you need to be very careful about the use of Ivermectin. Ivermectin is an ingredient in: Heartguard, Iverhart, Tri-Heart and Advantage DUO. Other drugs that can effect these breeds are: loperamide for diarrhea (commonly sold as Imodium), morphine, butorphanol (pain and cough suppression) and acepromazine (Ace, ACP, or Atravet).

Signs of Ivermectin Poisoning may include: excessive dilatation of the pupil of the eye,lethargy, stupor, coma, tremors, loss of coordination of the muscles, vomiting and drooling.

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