The MDR1 gene mutation causes life-threatening ivermectin toxicity in collies and related breeds. Genetic testing prevents potentially fatal medication errors.
Dogs with the MDR1 mutation who receive ivermectin or other P-glycoprotein substrate drugs suffer severe neurological toxicity that can be fatal. The genetic basis means the risk is entirely predictable and preventable. Genetic testing of all herding breed dogs before initiating any drug from the P-gp substrate list prevents this entirely avoidable welfare emergency. Many dogs have died or suffered permanent neurological damage from administration of standard parasite treatments without prior genetic testing.