What Is Ivermectin and How Is It Used in Dogs?
Ivermectin is an antiparasitic medication from the macrocyclic lactone family. In dogs it has two very different roles, and understanding the difference between them is the single most important thing on this page.
At a tiny dose, ivermectin is the active ingredient in many monthly heartworm preventives — it kills the immature heartworm larvae a mosquito transmits, before they can mature. At much larger doses, ivermectin is used off-label to treat mange (mite infestations such as demodicosis and sarcoptic mange) and certain other parasites.
The gap between these doses is staggering. The approved heartworm-prevention dose is 6 micrograms per kilogram (6 mcg/kg) once a month. The doses used for demodectic mange are 300–600 mcg/kg — given every single day — which is 50 to 100 times the heartworm dose. This is why ivermectin must be used so carefully, and why a single calculator has to treat these uses completely separately.
Ivermectin works by binding to glutamate-gated chloride channels in the nerve and muscle cells of parasites, paralysing and killing them. Mammals are normally protected because these channels sit behind the blood–brain barrier — but, as the next section explains, that protection fails in some dogs.
This calculator is built safety-first. Use it to understand the doses and the risks, but ivermectin — particularly for mange — must be diagnosed, prescribed and monitored by a veterinarian. For more, see PuppaDogs’ guides to ivermectin for dogs and Heartgard for dogs.
The MDR1 Gene — Why Some Dogs Cannot Tolerate Ivermectin
Some dogs carry a mutation in a gene called MDR1 (also known as ABCB1). This gene makes a protein, P-glycoprotein, that acts as a pump keeping certain drugs — including ivermectin — out of the brain.
In a dog with the MDR1 mutation, that pump is defective. Ivermectin can then build up in the brain and cause severe neurological toxicity — at doses that a normal dog would shrug off. The old veterinary saying, “white feet, don’t treat,” comes from this risk.
The mutation is most common in herding breeds and their mixes, including:
- Collies (the highest frequency — up to around 3 in 4 in some populations)
- Australian Shepherds and Mini Australian Shepherds
- Shetland Sheepdogs
- Old English Sheepdogs
- Border Collies
- German Shepherds, Long-haired Whippets, Silken Windhounds and others
The reassuring news: the low heartworm-prevention dose (6 mcg/kg) has been tested and is considered safe even for MDR1-affected dogs. The danger lies in the high mange doses — those can be fatal in an MDR1-affected dog.
A simple cheek-swab or blood test can determine your dog’s MDR1 status. Any herding-breed dog, or mixed-breed dog of unknown ancestry, should be MDR1-tested before receiving high-dose ivermectin. The calculator above will refuse to give a high mange dose for a dog that is MDR1-affected or an untested herding breed — and that is by design.
How the Ivermectin Dosage Calculator Works
The calculator first asks what the ivermectin is for, because the dose differs so enormously, and then asks the dog’s MDR1 status. It then:
- For heartworm prevention, shows the 6 mcg/kg monthly dose and steers you firmly toward an approved product.
- For mange, shows the dose range — but only if the MDR1 status allows it. For MDR1-affected dogs, and for untested herding breeds, it stops and warns instead of giving a dangerous number.
Enter your dog’s weight, choose the use, select the MDR1 status, then press Calculate Dose.
Ivermectin Doses for Dogs — By Use
| Use | Typical ivermectin dose | Notes |
|---|---|---|
| Heartworm prevention | 6 mcg/kg, once monthly | The only FDA-approved oral dose; safe even for MDR1 dogs |
| Sarcoptic mange | ~200–400 mcg/kg | Extra-label; veterinarian-directed only |
| Demodectic mange | ~300–600 mcg/kg, daily | Extra-label; veterinarian-directed; not for MDR1 dogs |
Heartworm Prevention Dose by Weight
| Dog weight | Monthly preventive dose (6 mcg/kg) |
|---|---|
| 10 lb (4.5 kg) | ~27 mcg |
| 25 lb (11 kg) | ~68 mcg |
| 50 lb (23 kg) | ~136 mcg |
| 75 lb (34 kg) | ~204 mcg |
These amounts are micrograms — thousandths of a milligram. They are far too small to measure reliably at home, which is exactly why heartworm preventives are sold as pre-measured, weight-banded products.
Never Use Livestock Ivermectin on a Dog
One of the most common — and most tragic — causes of ivermectin poisoning in dogs is the use of livestock products: 1% cattle or swine injectable solution, or horse deworming paste. These products are designed for animals weighing hundreds of kilograms and are extraordinarily concentrated. A dose error of a fraction of a drop can be lethal for a small dog.
Do not attempt to dose a dog from livestock ivermectin. For heartworm prevention, use an approved canine preventive. For mange, use what your veterinarian prescribes. This calculator deliberately does not convert doses into millilitres of livestock product.
Modern, Safer Alternatives for Mange
For decades, high-dose ivermectin was a mainstay of mange treatment. Today, that has largely changed. A class of drugs called isoxazolines — afoxolaner, fluralaner, sarolaner and others, familiar as flea-and-tick products — has been shown to treat demodectic and sarcoptic mange very effectively, with a wide safety margin and no MDR1 concern.
Because of this, many veterinarians now reach for an isoxazoline rather than high-dose ivermectin for mange. If your dog has been diagnosed with mange, ask your veterinarian about these modern options — they are often the safer and simpler choice.
Signs of Ivermectin Toxicity
Ivermectin poisoning is a medical emergency. Signs — which reflect the drug reaching the brain — include:
- Dilated pupils and apparent blindness
- Drooling and vomiting
- Unsteady, wobbly walking (ataxia) and weakness
- Muscle tremors
- Disorientation, depression or unusual behaviour
- Collapse, coma and seizures in severe cases
- Slow or depressed breathing
These signs can appear within hours of an excessive dose. If you see them, seek emergency veterinary care immediately and bring the product packaging. There is no specific antidote, but with prompt, intensive supportive care many dogs recover — though severe cases can be fatal.
When to See Your Veterinarian
Always involve your veterinarian before using ivermectin:
- Before starting heartworm prevention — a heartworm test is required first, because giving a preventive to a dog that already has adult heartworms can be dangerous.
- For any suspected mange — itching, hair loss and skin sores have many causes, and mange must be confirmed (usually by skin scrapings) before treatment.
- For any herding-breed or unknown-ancestry dog — discuss MDR1 testing.
- At the first sign of any possible toxicity — treat it as an emergency.
Conclusion
Ivermectin is a valuable antiparasitic drug for dogs, but it is also one that demands real respect. Its uses span an enormous dose range — from 6 mcg/kg monthly for heartworm prevention to 300–600 mcg/kg daily for demodectic mange — and the MDR1 gene mutation common in herding breeds can turn a mange dose deadly. The calculator above is built to inform and protect: it gives the low heartworm-prevention figure, but for mange it defers to MDR1 status and to your veterinarian. Use approved heartworm preventives rather than home-measured ivermectin, never use livestock products on a dog, ask about modern isoxazoline alternatives for mange, and let your veterinarian diagnose, prescribe and monitor.
Frequently Asked Questions
What is the correct ivermectin dose for dogs?
It depends entirely on the purpose. For heartworm prevention the dose is just 6 micrograms per kilogram once a month – the only FDA-approved oral dose. For mange it is far higher and extra-label: roughly 200-400 mcg/kg for sarcoptic mange and 300-600 mcg/kg daily for demodectic mange. The high mange doses must be prescribed and monitored by a veterinarian.
Why is ivermectin dangerous for Collies and herding breeds?
Many herding breeds – Collies, Australian Shepherds, Shetland Sheepdogs and others – carry a mutation in the MDR1 (ABCB1) gene. This mutation weakens the pump that normally keeps ivermectin out of the brain, so the drug can build up and cause severe, sometimes fatal, neurological toxicity. The low heartworm-prevention dose is still safe for these dogs, but high mange doses are not.
Is the heartworm-prevention dose of ivermectin safe for MDR1 dogs?
Yes. The 6 mcg/kg monthly heartworm-prevention dose has been tested and is considered safe even for dogs with the MDR1 mutation. The danger is specifically with the much higher doses used to treat mange, which can be fatal in MDR1-affected dogs. Always use an approved heartworm preventive at the labelled weight-banded dose.
Can I use horse or cattle ivermectin paste on my dog?
No. Livestock ivermectin products – cattle and horse injectables and horse paste – are designed for animals weighing hundreds of kilograms and are extremely concentrated. They cannot be measured accurately for a dog, and tiny errors are a common cause of fatal ivermectin poisoning. Use only veterinary-approved canine products at the dose your vet recommends.
What are the signs of ivermectin poisoning in dogs?
Signs of ivermectin toxicity include dilated pupils, apparent blindness, drooling, an unsteady or wobbly walk, muscle tremors, disorientation, weakness, and in severe cases collapse, seizures and coma. They can appear within hours of an excessive dose. If you see these signs, seek emergency veterinary care immediately and bring the product packaging.
Is ivermectin still the best treatment for mange in dogs?
Not necessarily. High-dose ivermectin was long used for demodectic and sarcoptic mange, but modern isoxazoline parasiticides (afoxolaner, fluralaner, sarolaner) now treat mange very effectively, with a wide safety margin and no MDR1 risk. Many veterinarians now prefer these. Ask your vet which option is safest and most appropriate for your dog.
Related PuppaDogs Calculators
Continue building your dog’s personalised care plan with these related PuppaDogs calculators:
- Dog Pregnancy / Whelping Due-Date Calculator
- Puppy Weight Predictor (Adult Weight Calculator)
- Heatstroke Risk Calculator for Dogs
- Bloat (GDV) Risk Calculator for Dogs
- Dog Life Expectancy Calculator (Breed, Body Condition, Lifestyle)
- Spay/Neuter Timing Calculator for Dogs (Breed-Specific)
References & Further Reading
The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.
- Plumb DC. Plumb’s Veterinary Drug Handbook. 10th ed. Hoboken, NJ: Wiley-Blackwell, 2023 – ivermectin monograph.
- Merck Veterinary Manual. Ivermectin and macrocyclic lactones; MDR1 (ABCB1) gene mutation and drug sensitivity in dogs. merckvetmanual.com.
- Washington State University Veterinary Clinical Pharmacology Laboratory (PrIMe). Multidrug sensitivity / MDR1 gene testing in dogs. vcpl.vetmed.wsu.edu.
- American Heartworm Society. Current Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm Infection in Dogs. heartwormsociety.org.
- PuppaDogs. Ivermectin for Dogs: Safe Parasite Treatment. puppadogs.com.
