Multidrug Resistance Gene (MDR1 Gene)

There are breeds and mixes of susceptible breeds of dogs that have a genetic predisposition to adverse drug reactions involving over a dozen different drugs. The most serious adverse drug reactions involve several antiparasitic agents (ivermectin, milbemycin, and related drugs), antidiarrheal agent loperamide (Immodium), and several anticancer drugs (vincristine, doxyrubicin, etc). These drug sensitivities result from a mutation in the multidrug resistance gene (MDR1 gene). Washington State University’s Veterinary Clinical Pharmacology Laboratory, who maintains the patent for this test, has indicated that Tollers are not listed as a breed affected by the mutation because they have not encountered a positive to date. This test is not licensed to any other entity in the USA. It is licensed in Australia and Europe.