Predicting Chemotherapy Reactions in Dogs: MDR 1
ByHi everyone!
What about chemo safety in dogs, anyway?
How do we know whether a given dog with cancer will tolerate chemotherapy?
Well, for some drugs, there is a test that can give us info. The test is for mutations in a gene called MDR 1, or ABCB delta 1. This gene make a protein that is responsible for pumping foreign agents (like drugs) out of body cells. When the pump does not work, toxicities are more likely. These toxicities can be dangerous, so it is wise to consider this before starting chemo, especially if your dog is one of the common breeds affected (see below).
Dogs with the MDR1 mutation may be more likely to have bad reactions to some chemotherapy agents including Vinblastine, Vincristine, and Doxorubicin. These reactions include possible suppression of a type of white blood cell (neutrophil), vomiting, diarrhea, and loss of appetite.
It is recommended that if the test shows mutations in the MDR 1 gene, the dose of these drugs be decreased by 25-30% and careful monitoring be conducted.
Breeds and percentage with MDR 1 mutation
Collies: 54.6%
Long haired Whippets: 41.6%
Miniature Australian Shepherds: 25.9%
Silken Windhounds, Australian Shepherds, English Sheepdogs, McNabs, Old English Sheepdog, Shetland Sheepdogs: 0.9% or less
German Shepherds (no percentage available)
You can have your dog tested at Washington State (link). Print out the link page for your vet.
(FYI: There are several other drugs that are listed at WASU’s Clinical Pharmacology Lab, that can have increased chances of side effects with MDR 1 mutations, but have little to do with dog cancer directly: Ivermectin, Selamectin, Milbemycin, Moxidectin, Loperamide (Imodium) , Acepromazine, and Butorphanol.)
More tools coming up for dog lovers who want the goods on full spectrum canine cancer care!
Best to all,
Dr Dressler
About the Author
Dr. Demian Dressler, DVM is known as the "dog cancer vet" and is author of Dog Cancer Survival Guide: Beyond Surgery, Chemotherapy & Radiation. Visit his blog and sign up free to get the latest information about canine cancer. Go to http://DogCancerBlog.com.
4 Comments
February 28th, 2009 at 8:29 pm
Thank you for including this in your blog. I have a mixed breed dog that is a “half” mutant and I am surprised that of all the owners that I have met whose dogs have gone through chemotherapy, not one had heard of this. It seems to me, particularly in susceptible breeds, this should be tested for before starting chemo.
March 7th, 2009 at 4:34 pm
Lisa,
you are not alone in your opinion!
Best,
Dr D
January 15th, 2010 at 2:41 am
Hello!
Being the owner of an affected dog I know this dangerous mutation too well. I also know several lists showing dangerous drugs. But what I really want to know is, what can be done, if my dog will get cancer? What chance do I have to get him through a chemotherapy without toxicities or even being dead?
Kind regards,
Kris
January 22nd, 2010 at 11:14 pm
Dear Kris,
I understand your concern. You will need to consider your case uniquely if it comes up. There are so many different outcomes and possibilities that it is easy to get lost. Generally, lower doses of the drugs that are on the list would be used, with extra careful follow up.
Best,
Dr D