Ivermectin Sensitivity

Some dogs are more sensitive to certain kinds of drugs than other dogs. Recent advances in molecular biology have identified the reason for this sensitivity: it is due a defect in a particular gene, the "multi-drug resistance gene" (MDR1). The only way to know if an individual dog has the mutant MDR1 gene is to have the dog tested. As more dogs are tested, more breeds will probably be added to the list of affected breeds.

One of the breeds that carries the mutation is the English Shepherd. An ongoing study at the University of California, Davis, has tested 91 English Shepherds and found that 14% of the dogs carried the mutation. The investigators conducting this study would like to have more information on English Shepherds. Anyone willing to contribute to the study -- a simple process, requiring only a cheek swab for DNA from your dog and your dog's pedigree -- should contact Katy Robertson. You can also request the study kit at their website. Participation is free, and results from individuals are kept confidential.

Problem Drugs

There are many different types of drugs that have been reported to cause problems, ranging from over-the-counter antidiarrheal agents like Imodium® to antiparasitic and chemotherapy agents. It is likely this list will grow to include more drugs as research progresses. Drugs that have been documented, or are strongly suspected to cause problems in dogs with the MDR1 mutation:

a.. Ivermectin (antiparasitic agent)
b.. Loperamide (Imodium®; over-the-counter antidiarrheal agent)
c.. Doxorubicin (anticancer agent)
d.. Vincristine (anticancer agent)
e.. Vinblastine (anticancer agent)
f.. Cyclosporin (immunosuppressive agent)
g.. Digoxin (heart drug)
h.. Acepromazine (tranquilizer)
i.. Butorphanol (pain control)

Potential Problem Drugs

The following drugs may potentially cause problems when given to dogs that have the mutation. Biochemical studies have shown that this gene has the potential to act on over 50 different drugs.

a.. Ondansetron
b.. Domperidone
c.. Paclitaxel
d.. Mitoxantrone
e.. Etoposide
f.. Rifampicin
g.. Quinidine
h.. Morphine