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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Predicting Chemotherapy Reactions in Dogs: MDR 1

Updated: December 12th, 2018

Hi 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

Leave a Comment

  1. Lori on October 6, 2022 at 8:37 pm

    My dog tested pos for double MDR mutation and is treating for lymphoma. Even low dose vincristine was presenting neurological side effects. He is currently in remission so we have adapted the LOP protocol to remove the vincristine and just continue oral chemo- CCMU and procarbazine for the remainder of the cycles.

  2. Susan Kazara Harper on June 1, 2015 at 4:10 pm

    Oh Elmer, we’re so sorry to hear that Dinky has passed. And we know how much it hurts. Every journey is unique despite all the statstics. But you did everything that you could for Dinky Dink, and she knew it. That’s what is the most important thing; all the years of love and joy together. I hope you can hold on to those beautiful memories and know that she would not have it any other way. She just couldn’t get through the last battle. The real victory though Elmer, is in those years together. No one can ever take them from you, and Dink would not want you to stay in sorrow. She’s in your heart forever.

  3. Elmer Jackson on May 14, 2015 at 7:27 am

    The almost same happened to me and my Dinky! Damn chemo made her so so sick then prednisone done nothing her neck swelled up so bad that it started bleadind , vet would not call us back!! Needless to say we went back to our regular vet that didn’t do chemo two weeks later and yesterday she died in my arms , I could not dare to see her suffer one more Minit, April 27 she was eating April 30 she had chemo may 1,started getting sick and not eating may 12 she was put to sleep….the sadist day of my life. Dinky dink was and still is my best friend and little shadow I don’t know what I’m going to do with out her…… 🙁

  4. paula and jack on July 13, 2010 at 6:27 pm

    i wish i had read this also before putting my dog jack on it. he first had a bleeding ulcer from 20mg 2x a day of prednisone and tetracycline that his vet put him on when i took him in because his glands under his neck were a little swollen. the blood test showed his hgt was 17, i think. he said he had hemolytic anemia or maybe cancer. he got weaker each day on the prednisone and his hgt was 8.9 a week later,at another vet, because the first one wouldn’t call me back and i had called during business hours. that vet didn’t take emergency calls or give blood, so i had to take him an hour and a half away at night to an emer. clinic. they didn’t know what caused it either and said i should get an ultrasound done. this pace didn’t know what it was and suggested i take him to va. tech, where he had gone 21/2 years ago. his blood went back to 17 or so. the first time he went there, his alt,alk levels were high and his liver was enlarged with spots,fever of 105, and supposedly his gall bladder was sluggish. no cancer. they gave him antibiotics,ursodiol. i read a high protein diet can cause big problems and his levels were fine for all that time on a low protein diet. then he was so bony and had muscle wasting, age 141/2, i started giving him more protein, chicken, neck bones, and he seemed ok. a couple months later i noticed he couldn’t get comfortable on either side of his body when laying down. i thought his hips were bothering him cause they were so bony. i forgot about his liver and the high protein. then his glands happened soon after that. so anyway, at va tech they caught the prednisone connection, did needle biopsies of liver and shoulder glands. no cancer in liver found, but lymphoma in glands and probably blood. lungs, heart clear. they said only option was chemo, didn’t mention testing first. it made him deathly sick for several days. they had given him the first dose, vincristine,l asparaganase, there, a fri. evening with cerenia. i took him home sat. with no cerenia. sat. evening it had worn off and they didn’t give me any to take home. i was so mad. he was so sick and nothing was open til mon. he had the black stools also. he had no appetite and felt bad for days on the next three weeks of chemo, even with cerenia. two weeks after doxorubicin, his glands were BIGGER. and he was weaker and had not much appetite. each time black stools. my vet gave him lixotinic to build up his blood. then said i needed to go somewhere to get him blood. took him back to va. tech and couldn’t find a blood match and said he had kidney failure. they flushed him out , but he never got his appetite back and felt worse the next week. i finally called around to find someone to match him up at the end of that week after coming home. blood was 12. something. he had hallucinations or seizures that kept getting worse and i had to put him to sleep. this all happened in two months. i just so wish i hadn’t given him prednisone, i had read it was bad. i should have said, shouldn’t i try to get him a blood transfusion. and put him back on a low protein diet and maybe the clavamox and baytril again and see what happens. if only i had been more intelligent and skeptical of him. knowing that most vets don’t even mention that high protein diets can kill a dog. i know of a couple, but one was five hours away, a friend had told me her daughters dog had the same thing. and the other was nearby, but she is very expensive and not very personable. or, if the vet at va. tech had known about testing before chemo, my beautiful, precious boy wouldn’t have went through hell for two months and be dead and i would still have him. sorry but i am sick and in shock, and will never forgive myself for being so stupid. even though i looked up a lot on the internet, i evidently didn’t read enough. i loved him so much and never thought we’d part so soon and in such a horrible way. be very wary of vets, they can kill your pet in a second !

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