Ivermectin is an amazing medication used to kill many different types of parasites. It’s most commonly used in monthly heartworm prevention. It is also used to treat ear mites as well as hair mites, which can cause mange. It is used to treat some internal parasites as well. Toxicity can occur if a dog is given an excessive dose of the medication (10 to 20 times the recommended dose). Additionally, certain dogs are genetically hypersensitive to the medication. In these dogs, ivermectin can pass directly to the brain and be toxic or even lethal. Sensitivity to the drug can also be seen in dogs or puppies that have overdosed on a similar medication in the past.
A genetic sensitivity to ivermectin can be seen in several breeds, but is more commonly seen in the following breeds:
- Old English sheepdog
- Shetland sheepdog (Sheltie)
- Australian shepherd
- German shepherd
- Longhaired whippet
- Silken windhound
- Border collie
- Dogs of mixed breeds that include herding breeds
This genetic sensitivity is due to a mutation in what is called the MDR1 gene. This mutant gene may make the dog more sensitive to several other medications as well. Not all individual dogs in the breeds listed above carry the mutant gene. The only way to know if an individual dog has the mutant MDR1 gene is through testing. To do the test, cells are scraped from the inside of the dog’s cheek and sent to a laboratory for genetic testing. Talk to your veterinarian if you are interested in having your dog tested.
If your dog has ivermectin toxicity, you may see any of the following symptoms:
- Dilated pupils
- Loss of appetite
- Trouble standing
- Slow heartbeat
- Difficulty breathing
Ivermectin toxicity cannot be reversed. If the drug was given within the past 4 – 6 hours, your veterinarian may induce vomiting and/or give your dog activated charcoal to help minimize the amount of ivermectin that is absorbed.
Additionally, your veterinarian may perform the following tests:
- Chemistry tests to evaluate kidney, liver, and pancreatic function, as well as sugar levels
- A complete blood count to rule out blood-related conditions
- Electrolyte tests to ensure your dog isn’t dehydrated or suffering from an electrolyte imbalance
Your veterinarian will work to keep your pet comfortable and will treat any symptoms that develop. Treatment will depend on the symptoms and may include giving your dog fluids directly into a vein (intravenously), nutritional support (possibly with a feeding tube), placing your dog on a ventilator, maintaining your dog’s body temperature, or administering medication to control seizures.
Remember, when given the proper dose, parasite preventives are safe and protect your dog from deadly parasites, such as heartworms. To prevent toxicity, always follow the recommended dose for all medications. If you have one of the breeds that is more susceptible to ivermectin toxicity, please speak to your veterinarian about the risks and benefits of ivermectin.
If you have any questions or concerns, you should always visit or call your veterinarian – they are your best resource to ensure the health and well-being of your pets.