Opioid analgesic
Butorphanol
Use a reduced dose — affected dogs are more sensitive
WSU — Is your pet at risk of an adverse reaction to common drugs? (dose tiers, genotypes, signs)Last verified June 16, 2026
Independent DVM review in progressButorphanol is an opioid used for pain control and as a pre-anaesthetic. WSU lists it among the drugs where MDR1-affected dogs are more sensitive and should receive reduced doses. As with acepromazine, the practical step is to flag your dog's MDR1 status before any procedure that may use it.
“Dogs that are MDR1 mutant/mutant or MDR1 mutant/normal should receive reduced doses of these drugs.”— WSU Veterinary Clinical Pharmacology Laboratory · source
Why MDR1 dogs react to Butorphanol
The MDR1 (ABCB1) gene encodes P-glycoprotein, a pump that limits how much of certain drugs reaches the brain and helps the body excrete them. Dogs with the MDR1 mutation cannot make a fully functional pump, so these drugs accumulate at the blood–brain barrier and cause neurological toxicity.
Signs of toxicity to know
WSU describes severe adverse reactions in affected dogs as tremors, disorientation, blindness, lack of muscle control, and death. If your dog shows these signs after a medication, treat it as an emergency and contact a veterinarian or emergency clinic immediately — this is not a wait-and-see situation, and it is not a question for a website.
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The breed sets the baseline likelihood of the MDR1 mutation. Only a DNA test confirms an individual dog's genotype.
This is general information, not veterinary advice for your dog. It does not diagnose or prescribe. Always discuss any medication decision with your veterinarian before acting — they know your dog's full picture, including its MDR1 status if it has been tested. See our disclaimer and how we research.