Certain breeds of herding dog, such as the Australian Shepherds and many of the Collie breeds are known to show sensitivity to certain medications such as parasite-control (Ivermectin), anti-diarrhoea agents (Loperamide), chemotherapy (Doxorubicin; Vincristine; Vinblastine), sedatives (Acepromazine), heart medication (Digoxin), immune-suppressants (Cyclosporin) or pain medication (Butorphanol). This is due to a mutation that can occur in the MDR1 gene which compromises the efficacy of the blood brain barrier. This barrier, which blocks most medications from entering into the brain, is compromised by the mutation, which causes a build-up of these medications within the dog’s brain. This can lead to neurological reactions such as disorientation, tremors, blindness, involuntary muscle movement, seizures or even death. Heterozygous dogs (carriers of the mutant allele) are not affected and can phenotypically be similar to a homozygous normal dog. However, they may transmit this disease to their offspring. Unistel Medical Laboratories offers a test to determine whether dogs have mutated copies of the MDR1 gene which could result in Type 1 Multi-Drug Resistance.