Is Ivermectin toxic to dogs?

Ivermectin acts as an anthelmintic that can cross the blood-brain barrier in sensitive breeds or at high doses, leading to central nervous system depression and severe neurological impairment.

Treatment removes as much of the drug as possible and supports the body while it wears off. If the exposure was within the last 4 to 6 hours, the vet may make your dog vomit or give activated charcoal. Some dogs need IV fluids and more advanced care. Vets may give an IV lipid (fat) emulsion, which has been used successfully in dogs that ate large amounts of ivermectin, although it seems less effective in MDR1-sensitive dogs. Badly affected dogs can need intensive nursing care for days or weeks, with support for breathing (some need a ventilator), the heart and circulation, and feeding.

Without aggressive treatment, ivermectin poisoning can be deadly. With appropriate care, the outlook for a full recovery is good, according to a study of Collies with severe, prolonged poisoning, but recovery is slow: most of them took 3 weeks. Pet Poison Helpline warns that MDR1-sensitive dogs need early, aggressive treatment and long supportive care to survive, and that even then many do not live.

• Horse dewormer pastes, such as Zimectrin. They contain large amounts of ivermectin, and many poisonings happen when a dog chews up a tube.
• Ivermectin products for cattle, pigs and other livestock, such as drenches, injections and medicated feed. Ivermectin is also sold under names such as Ivomec and Bimectin.
• Manure from horses, sheep or other animals that were recently dewormed. Dogs have been poisoned by eating it.
• Monthly heartworm preventives for dogs and cats, such as Heartgard and Iverhart. At the labeled dose they are considered safe, but eating a larger number of tablets may be a concern.
• Higher doses used off-label for mange and other skin parasites, and doses given by mistake, such as an overdose injected into a cat.

• Never give your dog or cat a dewormer made for horses, cattle or other livestock. These products contain large amounts of ivermectin.
• Give heartworm preventives only as your vet prescribes. At the labeled dose, ivermectin heartworm preventives such as Heartgard are considered safe even for dogs with the MDR1 mutation.
• If your dog is a collie, Australian shepherd, Shetland sheepdog, long-haired whippet or another herding breed or cross, ask your vet about an MDR1 test before any other ivermectin treatment. A genetic test is the only way to know, and reactions can happen in other breeds too.
• Keep horse dewormer tubes in a closed cabinet, not in an open tack trunk where a dog can chew them, and keep dogs away from manure of recently dewormed animals.
• Store heartworm preventives where pets can't reach them. Eating a larger number of tablets at once may be a concern.