Chemotherapy
Vinblastine
Reduced dose needed under oncology supervision
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 progressVinblastine is a chemotherapy drug in the same family as vincristine. WSU lists it among the chemotherapy agents that require dose reduction in MDR1-affected dogs to avoid severe toxicity. As with all chemotherapy, dosing is managed by a veterinary oncologist who accounts for MDR1 status.
“Dogs … should receive reduced doses … to avoid severe toxicity.”— WSU Veterinary Clinical Pharmacology Laboratory · source
Why MDR1 dogs react to Vinblastine
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.