Multi-Drug Resistance Gene, (MDR) codes for a protein that is responsible for protecting the brain by transporting potentially harmful chemicals away from the brain. In certain breeds, a mutation in the MDR1 gene causes sensitivity to Ivermectin, Loperamide, and a number of other drugs. As a result of the accumulation of toxins, the dog can show neurological symptoms including: ataxia, tremors, seizures, excessive salivation, obtundation, bradycardia, mydriasis, loss of menace, loss of papillary light responses, coma and respiratory arrest. Age of onset from birth, but symptoms only noted when exposed to drugs causing sensitivity.There are many different types of drugs that have been reported to cause problems. Some drugs include: Acepromazine, Butorphanol, Cyclosporin, Digoxin, Doxorubicin, Doramectin, Emodepside, Erythromycin, Ivermectin, Loperamide (Imodium), Milbemycin, Moxidectin, Paclitaxel, Rifampin, Selamectin, Vinblastine, Vincristine. Please note this list is not exhaustive and could be subject to change.