Ivermectin is a common drug used in the treatment of heartworms and other parasites in pets. Because the drug is so effective, millions of dogs will be treated with Ivermectin, the great majority without side effects or incidence. However, some breeds have a strong genetic sensitivity to Ivermectin, which can lead to serious adverse effects, even death.
Those pet owners with Collies, Australian Shepherds, Shetland Sheepdogs, Old English Sheepdogs, and English Sheepdogs should know the facts about Ivermectin intolerance. This knowledge could end up saving your dog’s life.
What Is Ivermectin?
Ivermectin is a neurotoxin, and is the active ingredient in a number of heartworm and parasite treatments. The drug is used in two ways: it helps prevent parasites from being attracted to dogs, and it kills parasites once infestation has occurred.
Ivermectin treatments may be given to dogs orally, by injection, or applied to the skin as a spot-on treatment. The drug is considered safe by most veterinarians, with a low side effect risk.
What Is Ivermectin Intolerance?
Though it’s safe for most dogs, certain herding breeds like the Collie have a genetic defect that prevents Ivermectin from being flushed from the brain. Ivermectin in Collies can build up in the brain over a period of time, or it can happen quite quickly, especially with the larger doses used for dogs already infected with heartworms.
The gene involved in this intolerance is the MDR-1 gene, or the multidrug resistance gene. Those dogs with a mutation in the MDR-1 gene lack a protein that allows certain drugs such as Ivermectin to be flushed from the brain. Thus, a dangerous level of toxicity can quickly occur.
Collies and other dogs can be both carriers of the genetic defect as well as affected by it. Carriers may pass Ivermectin intolerance to their offspring without being subject to the condition themselves.
Symptoms of Ivermectin Intolerance
Dogs with sensitivity to Ivermectin can show symptoms of toxic buildup in the brain within 4 to 12 hours of exposure to the drug, especially in the case of larger doses. Those dogs being treated preventatively for parasites with smaller doses can experience symptoms within 48 to 96 hours of exposure.
Among the most common of initial symptoms of intolerance is dilation of the dog’s pupils with an increased sensitivity to light. This dilation is unresponsive to the application of light from a flashlight or other device.
Appetite and Digestive Problems, and Drooling:
Another common early symptom in affected dogs is digestive problems. Your dog may lose their appetite or experience chronic bouts of vomiting. If left untreated, this vomiting can lead to dehydration. An affected dog may also exhibit excessive drooling.
Lack of energy is a third common early indication of Ivermectin intolerance, which can progress to an inability of your dog to rise to their feet.
More advanced symptoms include motor impairment as the drug begins to affect critical areas of the brain. Your pet may stumble or fall as they try to walk or stand. The dog may also appear disoriented and unresponsive to your voice or actions.
Breathing may become shallow and labored, and loss of consciousness may occur. The dog may experience seizures or fall into a coma. Without treatment, the affected dog may die.
Treatment for Ivermectin Intolerance
Should your dog experience any of the above symptoms, prompt veterinary treatment should be sought. Since intolerance to the drug is genetically based, the condition itself cannot be treated. Rather, your vet will try to control the more dangerous side effects.
To treat the effects, the veterinarian may give your dog fluids or drugs intravenously. Your dog may also be put on a ventilator, and may be given a feeding tube.
If the drug exposure was recent—within 4 to 6 hours—vomiting may be induced and gastric lavage and activated charcoal used to minimize absorption of the drug into the bloodstream. Depending on the level of exposure and response time to toxicity, your dog may require days to weeks of follow up care while your pet rests and regains their strength.
Preventing Ivermectin Toxicity
Given the potential severity of the effects of Ivermectin toxicity, and the difficulty in ameliorating them, the best course of treatment for the condition is prevention.
Those pet owners with Collies and other susceptible breeds should look for alternatives to Ivermectin for the treatment of parasites, several of which are available. Make sure to work with your vet to find the best alternative, since these same breeds can be intolerant to other drugs as well.
Your dog can also be tested genetically for Ivermectin sensitivity. Currently, all testing is performed at the Washington State University College of Veterinary Medicine. Test kits can be ordered from that lab, which use a check brush collection system. Samples are then mailed to the university.
Of course, as with any health problem your dog may experience, your vigilance is the first line of defense. Always keep an eye out for changes in your dog’s mood or behavior and contact your vet as soon as you suspect something may be wrong.
More on Medications for Pets
Comparing Flea and Tick Medications
Comparing Heartworm Medications
This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.