MDR1 Drug Sensitivity in Dogs
Emergency veterinary guidance on ivermectin toxicity and macrocyclic lactone sensitivity. Clinical protocols from veterinary toxicologists who have treated hundreds of these cases.
Why This Resource Exists
In over two decades of veterinary toxicology practice, I have lost count of how many dogs I have consulted on for ivermectin toxicity. Some walked out of clinics after a few days of intensive care. Others did not survive despite everything veterinary teams tried. What continues to frustrate me is that nearly every one of these cases was preventable.
The MDR1 gene mutation affects millions of dogs, particularly those from herding breed lineages. A simple genetic test costs less than a single night in the ICU. Yet owners continue to learn about their dog's sensitivity only after watching their pet seize on an emergency room floor.
This site exists because I am tired of those consultations. I am tired of explaining to families why their healthy Collie is now comatose. I am tired of drug companies burying warnings in fine print while marketing products that can kill susceptible dogs. And I am especially tired of the preventable deaths that keep showing up in emergency clinics.
What You Will Find Here
This resource provides clinical-grade information on MDR1 drug sensitivity, written by veterinary toxicologists who handle these cases regularly. We cover the mechanism of toxicity, the clinical signs at each stage, treatment protocols with specific medications and dosages, and practical guidance on prevention. For comprehensive information on MDR1 genetics and inheritance patterns, we recommend the detailed MDR1 guide at The Herding Gene.
This is not gentle reading for pet owners who want reassurance. This is the information you need if your dog is affected by MDR1 or if you want to prevent your dog from ever needing emergency services.
Clinical Articles
How Ivermectin Kills: The Mechanism Behind MDR1 Toxicity
January 28, 2026Understanding the molecular mechanism that makes ivermectin deadly for MDR1-affected dogs. Why the blood-brain barrier fails and what happens when the drug floods the central nervous system.
Safe Heartworm Prevention for Sensitive Breeds
January 25, 2026Not all heartworm preventatives are equal for dogs with MDR1 mutations. A clinical guide to selecting and dosing products that protect without poisoning.
Clinical Signs of Ivermectin Toxicity: A Veterinarian's Guide
January 22, 2026From subtle ataxia to complete unresponsiveness, recognizing the progression of ivermectin toxicity can save lives. What to watch for and when to act.
MDR1 Mutation Prevalence by Breed: Complete Statistics
January 13, 2026Comprehensive breed-by-breed statistics on MDR1 gene mutation prevalence. Which breeds are most affected by ivermectin sensitivity.
Understanding the MDR1 Gene Mutation: A Complete Guide
January 7, 2026Comprehensive explanation of the MDR1 gene mutation in dogs, how it causes drug sensitivity, and why genetic testing matters.
First Aid for Suspected Ivermectin Exposure in Dogs
January 1, 2026Emergency first aid guide for dogs who may have ingested ivermectin. What to do immediately and how to prepare for veterinary care.
About the Author
Dr. James Richardson, DVM, PhD is a board-certified veterinary toxicologist with over twenty years of experience in clinical and research toxicology. He has consulted on thousands of poisoning cases involving companion animals and has published extensively on drug sensitivities in dogs.
Dr. Richardson's focus on MDR1-related toxicities began during his doctoral research at Cornell University, where he studied P-glycoprotein function and genetic polymorphisms affecting drug disposition in dogs. He continues to research treatment outcomes in macrocyclic lactone toxicity cases and educates veterinary professionals on early recognition and intervention.
Full Biography