Multi-Drug Sensitivity in Dogs

I learned something really fascinating recently and thought that some of you might be interested in reading about it as well.

Apparently, some dogs are know to have bad reactions to some commonly used veterinary medications including: ivermectin, loperamide, Imodium, and many chemotherapeutics.  For many years, no one knew why this was happening and veterinarians were taught that if dogs had white feet, they "should not treat" them with these medicines. However, a few years ago researchers at Washington State University's College of Veterinary Medicine discovered that mutations in the mdr1 gene cause problems with coding of glycoprotein ultimately leading to difficulty metabolizing drugs effecting this protein. 

Dogs who have two copies of the faulty gene (one from each parent), who are then given normal doses of the drugs that contain the problem compound  are also likely to experience a dysregulation of the HPA axis (Hypothalmic-pituitary- adrenal). They often appear to have a slightly irregular version of Addison's disease which is actually caused by dysfunction of the adrenal glands and often co-occurs with and can lead to thyroid dysfunction if left untreated.

But normal dogs and dogs with only one copy of the gene are not susceptible to this problem so the drug could be used without concern in them and shouldn't be used at all in those who are homozygous (two copies of the gene).

Many breeds are know to carry the gene and it is highly prevalent in herding breeds, especially Collies. I was unable to find any specific information on the rate of this mutation in Standard Schnauzers but expect the rate to be low as Standards are relatively unrelated to the herding breeds (genetically speaking) despite their use as herding dogs. 

If you are interested in learning more about this subject, please see: http://www.vetmed.wsu.edu/depts-vcpl/

A printable information sheet can be downloaded from : http://www.vetmed.wsu.edu/depts-VCPL/printable/VCPL-Flier.pdf

There are also a number of scholarly articles that can be obtained with a quick Google search for scholarly articles on Mutlidrug Sensitivity in Dogs or by referencing appropriate search terms in the veterinary literature databases. I have not listed them all here because there are too many and my list would quickly be out of date as this literature appears to be constantly evolving.