Just a quick clarification, as the media has over-simplified this issue causing concern where none should exist, and complacency where owners should be more vigilant... typical media.
The issue you are referring to is the Multi Drug Resistance genetic defect (MDR1), where the blood/brain barrier in affected dogs is compromised, leaving these dogs unable to pump certain drugs out of their systems. For these dogs, drugs which are perfectly safe for unaffected dogs can be toxic.
This is an inherited defect; before breeding it is critical to test the parents to avoid parings which would pass on the defect. Testing is required within the collie and sheltie clubs in Switzerland and DE - sadly the US and UK kennel clubs are far too lax. (Which is why, 20 years on, the problem still exists.)
The defect was first noticed in the rough collie family, in response to Ivermectin. (Hence the internet meme.) However, the defect can affect many other breeds, and there is a whole long list of problematic drugs for affected dogs, from anti-parasites to anti diarrhea drugs, to opoids to chemotherapy. Recent research also suggests here are also immune system issues possibly related to the defect.
One should NEVER rely on breed alone when making decisions about the defect and drug safety. There is only one way to know if your dog is affected: do the test! It's a simple blood test or cheek swab, non invasive and fairly inexpensive.
The defect is widespread in the rough and smooth collies - some 75% of the population are either carriers (MDR1-/+) or affected ((MDR1-/-), the affected incidence is some 33%. All owners of rough amd smooth collies are advised to test their dogs . (Please note that we are talking about rough and smooth collies; border collies have a much lower incidence of affectation, some 0.03%) But it should be emphasized that one must test the individual - for instance, there are unaffected collies (MDR1+/+) for whom the listed drugs are perfectly safe.
According to the Giessen study, breeds showing incidence of the defect are:
http://www.vetmed.uni-giessen.de/pha...ekt/rassen.php
If one relies only on breed alone to make decisions, one risks giving toxic drugs to an affected dog - and on the other hand, one risks witholding a perfectly safe and necessary drug from an unaffected one. Both are worrying approaches - the only correct path is to test the individual, and proceed from fact .
I've had two MDR1-/- dogs, my collie Melon and my sheltie The Belltie. In hindsight we suspect that my first collie might have been affected, as we knew 'something' was not right with him, but the defect had not been identified all those years ago.
The defect played a part in many aspects of Melon's medical treatment; on several occasions we had to opt for less effective drugs to try to treat a condition due to toxicity concerns with the standard drug. Fortunately the Belltie has not been as dramatically affected.
My other rough collies and shelties are/were either carriers or unaffected; knowing their status I can/could safely give them drugs I could not give Melon or the Belltie.
Due to it's high incidence among the population, all rough collie owners should read the studies - owers of other affected breeds would be well advised to do so too.
The studies:
University of Giessen (DE)
http://www.vetmed.uni-giessen.de/pha...dr1_defekt.php
Washington State University (USA)
http://www.vetmed.wsu.edu/depts-VCPL/#Drugs
(Hopping off soap box now... sorry, it's a pet issue for me. Literally. )