Multidrug Resistance Mutation (MDR1/ABCB1) is a high-severity neurological condition that can affect dogs of all ages and breeds. The MDR1 (ABCB1) mutation causes a defective P-glycoprotein pump in the blood-brain barrier, allowing normally safe drugs (ivermectin, loperamide, certain chemotherapy agents) to accumulate in the brain to toxic levels. Affected dogs can die from routine doses. It is documented across 6 breeds, though prevalence and severity can differ significantly between them. It typically becomes apparent at Any age (drug-triggered). Early signs to watch for include neurological signs after drug exposure, tremors, ataxia, and seizures, blindness, and coma. When treatment is required, costs are estimated at £500-£3,000 per event depending on severity, location, and the specific intervention needed. Multidrug Resistance Mutation (MDR1/ABCB1) has a hereditary component, so health-screening certificates from the breeder are strongly recommended for predisposed breeds. This page covers symptoms, treatment options, and preventive steps — along with breed-specific information where available.

Signs & Symptoms

The following symptoms are commonly associated with Multidrug Resistance Mutation (MDR1/ABCB1) in dogs. If your dog displays several of these signs, consult your vet promptly — early diagnosis typically leads to better outcomes.

• Neurological signs after drug exposure
• Tremors, ataxia, and seizures
• Blindness
• Coma
• Death in severe cases

Treatment Overview

No treatment for the mutation itself. Management involves identifying mutation status via DNA test and avoiding all MDR1-sensitive drugs. If intoxication occurs, supportive care and lipid emulsion therapy may help.

Typical onset: Any age (drug-triggered)

Prevention & Screening

While not all cases of Multidrug Resistance Mutation (MDR1/ABCB1) can be prevented, the following steps reduce risk or enable earlier intervention:

• DNA test all herding breeds before drug administration
• Never use ivermectin at anti-parasitic doses in untested herding breeds
• Alert veterinarian to mutation status

Breeds Affected by Multidrug Resistance Mutation (MDR1/ABCB1)

The following 5 breeds are documented as being susceptible to Multidrug Resistance Mutation (MDR1/ABCB1). Click any breed to view breed-specific information about this condition, including prevalence and recommended screening.

• Rough Collie (large)
• Shetland Sheepdog (small)
• Australian Shepherd (medium)
• Border Collie (medium)
• Old English Sheepdog (large)