Yes, avermectin B1 (also called abamectin) is toxic to dogs. In laboratory studies with beagles, the lethal dose is around 8 mg/kg of body weight, making it roughly five times more toxic than its close relative ivermectin, which has a lethal dose of 40 mg/kg or higher. Dogs most commonly encounter abamectin through ant and roach baits, agricultural pesticides, or accidentally ingesting livestock deworming products.
What Avermectin B1 Is and Where Dogs Encounter It
Avermectin B1 is a pesticide used to control mites, cockroaches, ants, and other insects. It’s the active ingredient in many household insect baits and some agricultural sprays. The ASPCA lists avermectin alongside boric acid and fipronil as one of the most common insecticides found in ant and roach bait products, which are frequently left at floor level where dogs can reach them.
Chemically, abamectin is nearly identical to ivermectin, the widely used veterinary dewormer. The only structural difference is a single double bond between two carbon atoms. That small change makes abamectin slightly more potent and, importantly, more toxic. Sub-chronic toxicity studies in rats, dogs, and mice have consistently shown abamectin to be more toxic than ivermectin at comparable doses.
How It Affects a Dog’s Nervous System
Avermectin B1 works by overstimulating certain channels in nerve and muscle cells, effectively flooding them with inhibitory signals. In insects and parasites, this causes paralysis and death. In mammals, the brain is normally protected by a barrier that keeps these compounds out of the central nervous system. A protein called P-glycoprotein acts as a gatekeeper, pumping avermectin molecules back out before they can cross into the brain.
The problem arises when that gatekeeper doesn’t work properly. Some dogs carry a mutation in the gene responsible for producing P-glycoprotein (known as the MDR1 or ABCB1 gene). Without a fully functional version of this protein, avermectin molecules freely enter the brain and spinal cord, causing severe neurological damage at doses that would be harmless to other dogs. Breeds in the collie family are the most well-known carriers of this mutation, but it also appears in Australian Shepherds, Shetland Sheepdogs, Old English Sheepdogs, and several other herding breeds. Mixed-breed dogs with herding ancestry can carry it too.
Even dogs without this genetic mutation can be poisoned if they ingest enough abamectin. The mutation simply lowers the threshold dramatically.
Signs of Avermectin B1 Poisoning
Based on cases reported to the ASPCA Animal Poison Control Center, the most common signs of abamectin exposure in dogs are vomiting, loss of coordination (ataxia), excessive drooling, lethargy, dilated pupils, and diarrhea. These are primarily neurological and gastrointestinal symptoms, reflecting the compound’s action on the nervous system and its irritation of the digestive tract.
In more severe poisoning, signs escalate to tremors, seizures, blindness, a dangerously slow heart rate, and coma. Death can occur in the most serious cases, particularly when the dog has the MDR1 mutation or has ingested a large quantity.
Symptoms typically develop within a few hours of ingestion. For related compounds taken orally, peak blood levels in dogs occur roughly 2 to 4 hours after swallowing the substance. This means the window between ingestion and the appearance of serious symptoms can be quite short.
Which Breeds Are at Higher Risk
Any dog can be poisoned by a large enough dose of avermectin B1, but dogs with the MDR1 gene mutation face dramatically higher risk. The mutation is most prevalent in:
- Collies (up to 70% or more carry at least one copy)
- Australian Shepherds
- Shetland Sheepdogs
- Old English Sheepdogs
- German Shepherds
- Long-haired Whippets
- Silken Windhounds
Genetic testing for the MDR1 mutation is available through several veterinary laboratories and can be done with a simple cheek swab. If you own a herding breed or a mix with herding ancestry, knowing your dog’s MDR1 status helps you assess the risk from any avermectin-class compound, including common heartworm preventatives.
What Treatment Looks Like
There is no specific antidote for avermectin B1 poisoning. Treatment is supportive, meaning the veterinary team focuses on keeping the dog stable while the compound is metabolized and eliminated from the body.
If the dog is brought in soon after ingestion, decontamination (inducing vomiting or administering activated charcoal) may reduce the amount absorbed. Once symptoms have set in, treatment shifts to managing them directly. One approach that has shown effectiveness in recent years involves administering an intravenous fat emulsion, which binds to the avermectin molecules in the bloodstream and helps pull them away from nerve tissue. This is combined with IV fluids and close monitoring.
In severe cases where the dog’s breathing becomes dangerously slow or stops, mechanical ventilation may be needed. Dogs with serious poisoning should be monitored for at least a week, as symptoms can persist or reappear during that time. The duration and intensity of treatment depend heavily on how much was ingested and whether the dog carries the MDR1 mutation.
Recovery Timeline
The prognosis for avermectin poisoning is generally good when aggressive supportive care begins early. Mild cases may resolve within a day or two with treatment.
More severe cases follow a longer arc. In documented ivermectin poisoning cases in young Doberman Pinschers (a closely related compound with a very similar toxicity profile), clinical improvement began within about 12 hours of starting treatment. The dogs were able to eat soft food by day 3 and could walk with support around the same time, though limb weakness and blindness lingered. It took roughly 2 weeks for the dogs to appear clinically normal and a full month for depression and vision problems to fully resolve. Blood chemistry values also returned to normal within about 2 weeks.
Blindness is one of the more alarming symptoms for owners, but it is often reversible with time. The key factor in recovery is how quickly treatment begins after exposure. Dogs that receive care early, before the compound reaches peak levels in the brain, tend to recover faster and more completely.