Drugs To Avoid With The MDR1 Mutation

Updated November 28, 2020

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 having 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 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

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 specific questions, feel free to leave a comment below or ask your vet.

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

By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!
Have something to add? Comments are welcome below and will appear within 24 hours.


4 Replies to “Drugs To Avoid With The MDR1 Mutation”

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

  2. 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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