The Shetland Sheepdog, often known as the Sheltie, is a breed of herding dog that originated in the Shetland Islands of Scotland. Cross-breeds are also affected. Dogs carrying Mdr1-1 share a common ancestor that experienced remarkable evolutionary success, having contributed genetically to at least nine distinct breeds of dog. Due to this genetic mutation, affected dogs may exhibit sensitivity or adverse reactions to many drugs, including acepromazine, butorphanol, doxorubicin, erythromycin, ivermectin, loperamide, milbemycin, moxidectin, rifampin, selamectin, vinblastine, and vincristine. Due to this genetic mutation, affected dogs may exhibit sensitivity or adverse reactions to many drugs, including acepromazine, butorphanol, doxorubicin, erythromycin, ivermectin, loperamide, milbemycin, moxidectin, rifampin, selamectin, vinblastine, and vincristine.