Antiparasitic
Ivermectin
Safe at heartworm-prevention dose · dangerous at high (mange) doses
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 progressIvermectin is the drug most MDR1 owners worry about — but the answer depends entirely on the dose. At the low dose used to prevent heartworm, ivermectin is safe even for dogs with the mutation. At the far higher doses used to treat mange and some parasites, it causes neurological toxicity in homozygous (mutant/mutant) dogs and can cause toxicity in heterozygous (mutant/normal) dogs.
Why the dose changes the answer
Heartworm-preventive dose (~6 µg/kg)
Generally safeAt the FDA-approved heartworm-prevention dose, ivermectin is safe in dogs with the MDR1 mutation. WSU states the heartworm-prevention dose (about 6 micrograms per kilogram) is safe even for affected dogs.
Mange / high-dose treatment (~300–600 µg/kg)
AvoidThe much higher doses used to treat mange (about 300–600 micrograms per kilogram) will cause neurological toxicity in dogs that are homozygous for the mutation, and can cause toxicity in heterozygous dogs. WSU advises avoiding high-dose ivermectin in affected dogs.
I don't know the dose / not sure
AvoidIf you don't know which dose is planned, treat it as the cautious case and ask your vet to confirm the exact dose and indication before proceeding. Heartworm-prevention dosing is safe; mange-level dosing is not.
“While the dose of ivermectin used to prevent heartworm infection is safe in dogs with the mutation (6 micrograms per kilogram), higher doses, such as those used for treating mange (300–600 micrograms per kilogram), will cause neurological toxicity in dogs that are homozygous for the MDR1 mutation (MDR1 mutant/mutant) and can cause toxicity in dogs that are heterozygous for the mutation (MDR1 mutant/normal).”— WSU Veterinary Clinical Pharmacology Laboratory · source
Why MDR1 dogs react to Ivermectin
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.
Check Ivermectinagainst your dog's breed
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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.