Friday, September 4, 2015

Drug Sensitivity in Collies and other Herding Breeds

We are resharing a previous post we wrote back in September of 2012, because there have been some recent illnesses in dogs due to drug sensitivities.  Please read our post below, and then click on this Link and print out the info from the American Working Collie Association.  Keep a copy and give a copy to your veterinarian.  Not all veterinary practices are aware of the MDR-1 drug sensitivity in certain herding breeds.

Drug Sensitivity in Collies

Many herding breeds have adverse reactions to a particular list of drugs, and collies are known to be one of these breeds.  This adverse reaction is the result of a mutation in the multidrug resistance gene, or MDR1 gene.  Not all collies have this mutation, but many of them do, so most collie owners will avoid these drugs or have their dogs tested for the gene.  This drug sensitivity can result in blindness, coma and death, so it is very important that collie owners, and the owners of other herding breeds like Aussies or Border Collies, become familiar with the names of these drugs.  There are veterinarians who seem to be unaware of this issue, and prescribe drugs or anesthesia that can be potentially fatal to your dog, so you need to make sure your veterinarian is aware of the risk.  You need to make sure that your dog is not given any of the following drugs if he/she has not been tested or if they have tested positive for the MDR1 gene:

Ivermectin – The dose of Ivermectin used to prevent heartworm infection in products like Heartguard is considered SAFE in dogs with the mutation. (6 micrograms per kilogram) However, because of reports of collies becoming ill on even this lose dose of Ivermectin, most collie owners are not willing to take the risk with their dog’s health.  As a result, most collie breeders and rescue groups advise new collie owners to use another heartworm preventative, such as Interceptor.  Ivermectin causes neurologic toxicity in some, but not all Collies, at doses that are 1/200th of the dose required to cause toxicity in other dogs.

Loperamide – (Imodium.) At doses used to treat diarrhea this drug will cause neurologic toxicity
in dogs with the MDR1 mutation. This drug should be avoided in all dogs with the MDR1

Selamectin, milbemycin, and moxidectin (antiparasitic agents.) Silmlar to ivermectin, these
drugs are safe in dogs with the mutation if used for heartworm prevention at the manufacturer’s
recommended dose. Higher doses (generally 10-20 times higher than the heartworm prevention dose) have been documented to cause neurologic toxicity in dogs with the MDR1 mutation.  Because Interceptor contains such a small amount of milbemycin, it is considered to be of low risk to collies and herding breeds.  But you will need to be sure to keep Interceptor, along with other drugs, safely out of reach of your dogs.  Because ingestion of multiple doses at one time can be fatal to your dog.

The reason the dosage of these drugs has to be carefully monitored, is because MDR1 causes a buildup of these drugs in the brain of the affected dog.  This buildup can cause neurotoxicosis, which can be fatal if left untreated.  If you notice your dog reacting oddly after exposure to any of these drugs, usually 4 to 12 hours after ingestion, dog owners are advised to seek veterinary care immediately, do not wait.  Some of the signs of an adverse reaction are:

Dilated pupils (the center of the eye will be abnormally large)
Digestive problems (loss of appetite and/or vomiting)
Heavy drooling
Depression or motor instability (the dog may have difficulty standing or walking, may have tremors, or weakness)
Seizures (blankness, disorientation, stupor, involuntary muscle movements and unconsciousness)

While this drug sensitivity may frighten many people, dogs still need to be kept on a monthly heartworm preventative.  (A heartworm infection is fatal if left untreated, and can be easily prevented.)  Herding breeds are loving, devoted companions, and this genetic mutation does not affect their temperaments.  Choosing a dog from one of the many wonderful herding breeds, to add to your family, will be a rewarding experience.  But it requires that you educate yourself on which drugs your dog can be given, and seek safe alternatives to keep your dog healthy and happy.  Afterall, they are worth it! 


  1. Maggie seems to be our drug sensitive dog at our house, sometimes gussie but nevers me. Have a great weekend.
    stella rose

  2. This is a really good and important post -- I've heard of these drug sensitivities because I've had friends that have had Collies, and I've fostered dogs that I know were mixed with Collie. It's something every one should be aware of.

  3. So glad I stopped by today, the vet where I worked asked me if we ever did this test and I said no, so this was great to get this info so then I can look it up as she has a collie mix she wants to check into it on. Thank you for stopping by Sand Spring Chesapeakes and watching my puppies grow. They are already leaving for their new homes.

  4. Fantastic post. I was just talking with my friend about this that has an Aussie who is n/n. She recently got sheep and was asking me about my guys because of needing to worm the sheep. Teach is m/n but I didn't know about Tucker yet. So sent off his test yesterday that I had got from WSU a few weeks ago. This is always a great reminder for people with herding breeds, its not just in Collies.

  5. I think that we'll print this out for our vet (just in case). We have two shelties and as they say, "better safe than sorry". We'll check out the shelties just in case. Thanks for the useful caution.

  6. Dad got a paper with all those drugs from Lil. He also taught our Dr. Waddel, our vet, about those sensitivities.

    Sherman & Gemini

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