Caleb is an Australian Shepherd that excels in agility. He became very ill after being treated with an Ivermectin product; he was rushed to the ICU, in a coma, and put on a ventilator.
He improves daily and is expected to recover, but you can imagine the trauma this has caused for his owner -- and the vet bills.
An MDR1 gene mutation has been discovered that makes Ivermectin and other drugs toxic for some dogs, especially the herding breeds. Dogs that carry the MDR1 genetic defect have trouble removing certain drugs and toxins from the brain, and the buildup can cause neurological abnormalities (tremors, seizures, blindness, coma) and even death.
Ivermectin is a commonly prescribed drug used to prevent heartworm. Although the amount of Ivermectin in monthly oral medications, such as Heartguard, is very low and not problematic, much higher doses of Ivermectin are used to treat mange and should be avoided in dogs with even 1 copy (of 2) of the mutant gene. Fatal overdoses of Ivermectin can also result from dogs eating manure in pastures where horses or sheep have been dewormed.
Other drugs that adversely affect dogs with the MDR1 mutation include loperamide (Imodium) to control diarrhea; acepromazine (Ace, Atravet), a tranquilizer; Erythromycin; and some chemotherapy drugs.
Seventy percent of Collies have at least 1 copy of the mutated MDR1 gene. Other breeds frequently affected are Australian Shepherds, Shetland Sheepdogs, German Shepherds, Long-haired Whippets, Silken Windhounds, and many mixed-breed dogs that may be crosses of these breeds. There is no way to know if a dog is affected without doing a DNA test. As more dogs submit DNA samples, other breeds will likely be added to the list.
For a more complete list of breeds, and drugs, check the website of Washington State University, Veterinary Clinical Pharmacology Lab. WSU offers the genetic test to find out if your dog has the mutant gene. A veterinarian can mail in a blood sample for analysis, or you can send for a kit to obtain a DNA sample from your dog's cheek cells using a swab, then mail it back to the WSU lab ($70).
Please spread the word so that other dogs do not suffer like Caleb.
Briards are not listed (so far) as a breed usually affected, but they are a herding breed. I decided it was worth the money to find out conclusively if I need to be cautious about this, for Chou Chou, in the future; I submitted a DNA sample for MDR1 genotyping. Good news: her results show that both copies of her MDR1 gene are normal.
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