About ten years ago I looked into this because my male standard was having a bad reaction to his flea/heartworm medicine. I must have read over a dozen research papers and lo, and behold, several of the papers mentioned that although not common, there had been cases of MDR1 in white Standard Poodles. Of course, my male is white. So, I talked to some friends that have Australian Shepherds and they recommended using Revolution because their breeders had used that when they had MDR1 dogs. Have not had a problem since,but Revolution does not cover the tick that causes Lyme, so that means I have to take other measures when we travel. I have to add that this dog is the one that has been borderline Addisons since he was a pup, so it is not easy to tell why he reacts to meds the way he does. Also, it was so long ago that I looked into the studies that I am not sure about the sources, For some reason I think that maybe it was a university in Oregon that had one study actually listing affected breeds, with herding dogs and sighthounds being the most commonly afflicted.