Drug sensitivity - MDR1?

[jami74]

We've been using a prescription topical flea treatment for our boy containing imidacloprid and moxidectin. Last month as he'd gone up a weight band he had the bigger pipette and was quite poorly afterwards. He started off just seeming very tired but then started looking uncomfortable and stiff when moving. I put him to bed early in a dark quiet room and when I went to check on him a couple of hours later he was sat in the middle of the room with his head hanging and took quite a bit of coaxing to move. I offered him a drink of water, which he had and put him back to bed. Twice in the early hours he needed to go outside with a runny tummy, in the morning he looked brighter and during the course of the day returned to his normal self (although we didn't take him out other than for toileting). He has been scratching ever since although we've not seen any fleas. I've spoken to our vet and we've been switched to a new oral flea treatment that contains afoxolaner which is apparently 'safe for Border Collies'. We haven't used it yet.

Anyway, I know his reaction might have been coincidence and unrelated but I wondered if it could be indicative of an MDR1 mutation. Is there much point in doing genetic testing? He won't be used for breeding and regardless of the result we'll avoid that class of antiemetics. The only other potential problem I can see is when we get him neutered, there'll be anaesthetic, might it be more risky if he does have MDR1 mutation? 

[GentleLake]

The letters stand for multi drug resistance, the meaning of which should be self evident. If the dog has the mutation, he's liable to react to a variety of medications.

If you have concerns that he might react to other medications, you should base your decision to test for the mutation based on this, not simply on the fact that he won't be bred.

[Hooper2]

Here is the list of drugs that dogs that carry the MDR1 mutation have been shown to be sensitive to, along with a list of other drugs that the human form of the MDR1 gene interacts with but have not been shown to be a problem in dogs.  http://vcpl.vetmed.wsu.edu/problem-drugs

Regarding surgery, your two biggest concerns would be acepromazine and butorphanol, which are sometimes given before anesthesia.  The MDR1 mutation is not very common in border collies, but neither of those drugs is essential for surgery, so, as a precaution you can ask your vet to not use them.   

I don't want to downplay the importance of the MDR1 mutation, but also keep in mind that dogs (and people) can have adverse reactions to all kinds of drugs even if they don't carry the mutation.  Not every drug reaction or health problem is MDR1 related even in dogs that do carry the mutation.  On the other hand, the cost of the genetic test is $60, which as veterinary expense go, is not terribly expensive (the cost of one Starbucks latte per month for a year), so if you are concerned, here's how you can get the test done http://vcpl.vetmed.wsu.edu/pricing

[terrecar]

Thanks Hooper2. I’ve been keeping an eye on that list as well, because although my Border Collie is clear, my Aussie/Border Collie mix has not been tested yet. Since I believe Aussies have a higher documented incidence of having the MDR1 gene, I was going to have her tested via Wisdom Panel, but the test at the link you provided offers a lower price.

Jami74: Moxidectin is on that list, but I’m not suggesting anything can be concluded from that, especially since:

”Higher doses (generally 10-20 times higher than the heartworm prevention dose) have been documented to cause neurological toxicity in dogs with the MDR1 mutation.”

And of course you’re using it as a topical.

[jami74]

Thanks everyone for your replies.

Yes, I read that moxidectin in normal doses shouldn't cause a problem even in dogs with the MDR1 mutation and I'm not sure his symptoms were particularly neurological, it is of course possible he managed to eat something yukky at the park that morning although it would have had to have been quick for me not to notice.

I'll discuss with the vet at our next appointment about getting tested and precautions meanwhile.