Drugs To Avoid With The MDR1 / ABCB1 Mutation

Updated August 15, 2023

Recently I’ve seen two Australian Shepherd puppies sold with a list of 52 drugs to avoid. I understand the intention, but this list is incorrect and alarmist. It contains many perfectly safe drugs, some of which will be essential later in life.

Yet who would use them after reading this:

Not every Australian Shepherd will have a negative or deadly reaction to the drugs listed above. However enough of them have had severe reactions and/or died to warrant caution. YOU must be an advocate for your Australian Shepherd.

source: Do Not Use Drugs For Australian Shepherds.

Despite preventing the use of many safe drugs, the list of 52 has also missed a few that may be toxic. So here’s your guide to which drugs to avoid in dogs with the MDR1 mutation.

What Is MDR1 Multi Drug Resistance?

The MDR1 gene (now also called ABCB1) codes for P-glycoprotein, a cellular pump responsible for the transport of certain chemicals. Mutations in this gene cause faults or delays in the removal of some drugs from cells. This is most evident in the brain.

Dogs with the MDR1 mutation are at risk of serious drug toxicities at doses that are safe to other dogs. In some cases these can even lead to death.

Which Breeds Are Affected?

The following list shows the common dog breeds most likely to have the MDR1 mutation, and the percentage affected in each.

Breed% source1% source2
Australian Shepherd5034
Shetland Sheepdog1523
White Swiss Shepherd15
Herding Breed (cross)10
German Shepherd102
Old English Sheepdog58
Australian Cattle Dog3
Border Collie<5<1%

It’s possible, though unlikely, for any dog to carry the mutation (rarer breeds can be found at both sources). Importantly, if you have a high-risk breed, or just want to be sure, you can easily get your dog tested at your local vet. It’s worth it!

MDR1 Drug List: Safe vs Avoid

The following drugs may have delayed transport in dogs with the MDR1 mutation. Some remain safe, others should be avoided.

DrugForAction Requiredsource
IvermectinHeartwormDon’t use1
MoxidectinHeartwormSafe at regular doses
SelamectinHeartwormSafe at regular doses
MilbemycinHeartwormSafe at regular doses
SpinosadFleasAvoid unless alone
EmodepsideWormsAvoid (rarely used)
AcepromazineSedationReduce or don’t use
ButorphanolSedation/PainReduce or don’t use
ApomorphineInduce vomitingReduce or don’t use
MorphinePainUse with caution2
BuprenorphinePainUse with caution2
FentanylPainUse with caution2
CyclosporinImmune systemMonitor drug levels
DoxycyclineAntibioticSafe at regular doses
ErythromycinAntibioticAvoid (rarely used)
DigoxinHeart diseaseMonitor drug levels
[many drugs]ChemotherapyCheck all before use3
LoperamideDiarrhoeaDo not use
OndansetronTreat vomitingUse with caution
  1. Ivermectin is reported safe at heartworm prevention doses but there are better drugs available
  2. Opioid pain relievers are essential drugs, and appear safe if used with care
  3. Many cancer chemotherapy drugs can cause severe or fatal toxicity
  4. Isoxazolines like NexGard, Simparica and Bravecto are very important for tick prevention and appear safe to use

These are likely to be the only common drugs your dog may encounter but we cannot guarantee accuracy as our knowledge is incomplete. If you have any questions about specific drugs, check with your vet or browse the questions below.

Related: Brand names of the common heartworm and flea products that contain the drugs mentioned

Have something to add? Comments (if open) will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.

22 Replies to “Drugs To Avoid With The MDR1 / ABCB1 Mutation”

  1. Hi what pain medication is safe to use on my Aussie w Proposol??
    She’s MDR1 and going in for surgery.
    Thank you

    1. Hi Christy. Given the large number of choices, it’s easier to say what to avoid, and you’ll find those listed in the article.

  2. First time I gave Nexgard Spectra to my 8months border collie heeler x she turned mad within 12 hours after chewing the tablets. She constantly shook her head, trembled, walked lobsided and became aggressive – probably due to pain or headache. I had to lock her in the crate for her and my safety. I felt so sorry for her; it was really scary too.
    I have been since searching for a safe allrounder product, but it is very confusing. We live in country Victoria and have farm animals. What should I do?

    1. Hi Becky. That sounds like a version of the well-known side effects of this class of drug, rather than anything specific to MDR one. You are best to avoid these products, as there are plenty of good flea controls such as Comfortis. However if ticks are a risk than please talk to your vet about what to do in your local area, because there are no products of equal efficacy.

  3. is there a best multi treatment for a border collie x. Im currently using NexGard Spectra, dont know if he has the Gene, but Pet barn says I should be using alternative brands. what is your opinion. my Border collie is 1 yr old and 24 kg. he has Gastro issues and is on a hypoallergenic diet.

    1. Hi Shirley. It’s more likely that a particular staff member at PetBarn has advised this, rather than it being policy of the organisation. As you’ll see, there is no reason for that combination to be of concern. As for what is the best, all you need to worry about is making sure that all the drugs you use are not featured in the list above.

  4. Hi Andrew,
    Can I ask have you ever heard of collies with the MDR1 mutation being ‘immune’ to anaesthetic? Trying to work out which components might be less effective for them (ACP/Meth premed, Propofol, Isofluorane). Thank you

    1. Hi Ellie. No, I have never heard of this and having anaesthetised many myself, I can attest that they respond identically to all of the drugs you mention, though I have not used alfaxalone.

    1. Hi Jody. Yes, Bravecto NexGard and Simparica are just as safe in Australian shepherds as in any other breed of dog.

  5. What about safe oral tick treatments? The information out there is so overwhelming:(

    1. Hi Shona. That’s why I wrote this page. There’s a lot of bad information out there leaving dogs without vital treatments. Bravecto, NexGard and Simparica appear safe for dogs with the MDR1 mutation and of course are nearly essential in paralysis tick areas.

      1. Andrew your andwers to some of these MDR1 gene and seizures are confusing and you’ve contradicted yourself as to your recommendations on the flea and worm issues and what’s safe
        A question was posted telling you a dog had seizures after nexgard and you recommended comfortis and to others you say that nexgard is safe for MDR1
        Please clarify what’s really true. Our dogs are our babies.

      2. Hi Jane. If you stick to the main body of the article you will find a very clear list of drugs to avoid. What you see in the comments are people asking about all sorts of things. The comment regarding seizures refers to a known link between isoxazoline insecticides and dogs prone to seizures, and has nothing to do with the MDR1 gene. Your confusion is a good example of the problem with forums on any subject.

  6. What is a safe flea preventative to use for aussies with the gene mutation? I’m having trouble finding one I can trust.

  7. We have construction going on outside our home. Our Australian Shepherd is shaking and very anxious when the hammering and air guns go off. I have trazodone that was given for our golden retriever for travel two years ago, is it safe to give the Aussie 1/2 tablet (each tab is 50 mg). Can’t get ahold of my vet right now. Will keep trying to contact vet. Thank you

    1. Hi Judy. In general, I won’t ever be able to recommend using a prescription drug without direct authorisation from your vet. However, trazodone is not known to be a problem in dogs with MDR1 mutations and it’s generally considered a very safe drug.

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