Our genetic makeup helps to make us who we are. We now have the ability to understand why some dogs and cats react to certain drugs differently. There is a genetic mutation (MDR1) that alters the transportation of certain drugs through our bodies. In dogs with the mutation, the genetic alteration can be complete (homozygous) or partial (heterozygous). Dogs with the homozygous gene mutation require lower doses of the drugs to achieve the same effect as a dog without the mutation (or heterozygous). What does this mean? Some drugs should probably be avoided altogether, but other medications just need to be given at a lower dose to avoid toxicity issues. At this time, there is a list of drugs known to cause issues in people, but the same effect is not necessarily seen in dogs. There is much research that still needs to be done to have a more complete canine list of potential drugs. This issue also affects cats, but there is not as much information available at this time.
Testing for the genetic mutation in dogs can be done through Washington State University using a cheek swab or a blood sample. For more information go to https://vcpl.vetmed.wsu.edu. Testing may also be performed through Royal Canin. Go to marsveterinary,force.com/royalcaningha for more information. Some of the drugs that have been identified to cause issues in animals with the gene mutation are:
Analgesics/ tranquilizers - acepromazine, butorphanol
Chemotherapeutic drugs - doxorubicin, actinomycin D, vinblastine, vincristine, vinorebline
G.I. agents - loperamide, ondansetron
Antibacterial - erythromycin, doxycycline?
Macrocyclic lactones - ivermectin, selamectin, milbemycin, moxidectin
Drugs such as heartworm preventatives are considered safe when taken at the recommended dosages for all dogs. However, they can still have adverse reactions not related to the gene mutation and higher doses that are used for treating mange can cause serious neurologic problems in dogs with the mutation. I would recommend testing any dog that is a breed known to have this mutation or any dog that is in need of chemotherapy.
1. Drug information obtained through Plumb's Therapeutics Brief "How should I treat dogs and cats with MDR1 mutation?"