Good news for dogs with demodex and MDR1 mutation (collies, shepherds, etc.): Isoxazolines instead of ivermectin for parasitic diseases | Twin Trees Vet Talk (PODCAST)

On today's episode of Twin Trees Vet Talk, we welcome our very special guest, Dr. Vincent Defalque. Dr. Defalque is a Board Certified Veterinary Dermatologist in Vancouver, BC (Canada). We hear about a 6 month old Australian Shepherd puppy named Kenny that Dr. Defalque saw for a severe skin disease caused by demodex, a mite that lives in the hair follicle (this disease is often called demodectic mange or demodecosis). The classic treatment usually takes an average of 10 weeks with daily oral ivermectin, and the disease can be notoriously difficult to treat. Because ivermectin is not safe to use in all dogs (Australian shepherds, collies and several other breeds often have a genetic mutation that causes them to become very sick or even die if given ivermectin), Dr. Defalque used a new class of drugs called Isoxazolines off-label to help this puppy. And it worked!

We hope you enjoy this episode! Please leave your questions and comments below!

P.S. I just want to add a quick apology to Dr. Defalque for taking more than a year from the time of our interview to finally edit and publish this episode (my excuses: busy life, chronic computer problems, and general burnout/ aversion of the veterinary profession). I appreciate so much you taking the time to share your knowledge and expertise!

About Dr. Vincent Defalque, DVACD:

Following graduation from the University of Liege (Belgium), Dr. Defalque completed an internship at Vet’Agro Sup (France), then a dermatology residency at Michigan State University. He became a board certified veterinary dermatologist in 2006. Dr. Defalque is a Past-President of the Canadian Academy of Veterinary Dermatology, and currently serves as the Canadian representative at the World Association for Veterinary Dermatology. Dr. Defalque works at North West Veterinary Dermatology Services in Vancouver, BC and St. Albert, AB. His special interests include the diagnosis and management of ear diseases in dogs and cats as well as feline dermatology.  

Do you have any most memorable/ inspiring cases? (Summary courtesy of Dr. Defalque): 

"We all have patients that we will always remember. This is certainly the case with an Australian Shepherd puppy called Kenny, a patient that I saw in the fall of 2015.
Kenny had demodicosis, a common skin disease caused by the proliferation of a mite called Demodex. The lesions were on his face. He also had a severe secondary
bacterial infection caused by an antibiotic resistant Staphylococcus. The skin infection was making this poor puppy so itchy that he had to wear an Elizabethan collar 24/7!

Because of the age and the breed of the patient, it was not safe to use the classic treatment at the time, which was oral ivermectin. But a new class of antiparasitic veterinary drug called isoxazolines had recently become available in Canada. At the time, these drugs were only labelled for the treatment of fleas and ticks, but there was some early scientific evidence for extra label use for the treatment of Demodex mites. I must admit that I was skeptical at first about the fact that these new medications would lead to a cure, because this skin disease was historically difficult to treat. It usually took an average of 10 weeks of daily oral ivermectin to achieve remission. I decided this was a great opportunity to treat my first case with a single dose of oral fluralaner. When I saw Kenny for subsequent rechecks, I was astonished. It worked, and it was well tolerated!"

Before and after photos and link to CVJ paper:

"Isoxazolines for treating canine demodicosis, sarcoptic mange (scabies), and lice infestation"

Why couldn't Kenny be given Ivermectin (the classic treatment for demodectic mange) ?

The MDR1 (now called ABCB1-1) genetic mutation leads to a problem with drugs and medications that are normally safe at the prescribed dose to be toxic or even fatal in individuals that have the mutation. The notorious drug to avoid is ivermectin (I've seen dogs die from this)- it is a common livestock dewormer that is also on the shelf at most vet clinics. Certain sedatives are also problematic, making anesthesia more risky if the hospital staff have not been made aware that the pet has the mutation.

Even dogs without the mutation can become intoxicated with ivermectin by ingesting an overdose of livestock dewormer, ingesting the feces of an animal (horse, sheep, etc.) that was recently dewormed, or from being given an overdose of ivermectin by an owner or breeder who did not calculate or measure the dose correctly.

Here is a great explanation of the MDR1 (from veterinartpartner.vin.com).   

"In normal patients, the P-glycoprotein is involved in keeping drugs out of certain tissues and is important in keeping ivermectin out of the patient's nervous system. A healthy P-glycoprotein system is what allows ivermectin to be safe for mammals, even in very high doses. Unfortunately, collie-related breeds (and some other breeds) commonly have a mutation in the genes that make P-glycoprotein. (This has been called the MDR1- mutation but has recently been renamed the "ABCB1-1" mutation.) This mutation can create dangerous ivermectin sensitivity. Normal commercial heartworm preventives do not use high enough doses for this issue to come into play; it is usually during treatment of demodectic or sarcoptic mange when the issue comes up.

Because of the prevalence of the P-glycoprotein gene mutation, genetic testing is recommended for dogs of the following breeds: collie, Shetland sheepdog, Australian shepherd, Old English sheepdog, long-haired whippet, and possibly other herding breeds. This is a DNA test using an oral swab. Test kits, which use a simple cheek swab, can be ordered directly from the Washington State University Veterinary School."