Adverse reactions to anesthesia: It’s not just greyhounds

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A rare genetic mutation could result in some canine patients being exposed to dangerously high levels of certain anesthetic agents.

Veterinarians have known for years that some greyhounds struggle to break down these drugs, which include several thiobarbiturates—such as thiopental and thiamylal—as well as propofol, resulting in potentially life-threatening and prolonged recovery periods following anesthesia.

Scientists at Washington State University (WSU) set out to figure out why. During a recent study, they found a genetic mutation common to greyhounds that also turned up in other common breeds. The previously unknown genetic mutation causes greyhounds to produce less of an enzyme called CYP2B11, which breaks down these drugs.

So when they found the same mutation in several other dog breeds closely related to the greyhound—including the whippet, borzoi, and Scottish deerhound—it wasn’t much of a surprise.

Then the team dug a little deeper, extending their survey to more than 60 other breeds. And that’s when things got interesting.

The researchers discovered that some popular dog breeds, including golden retrievers and Labrador retrievers, may also struggle to break down these commonly used anesthetics.

“We started with a condition we thought was specific to greyhounds and affected a relatively small number of dogs,” said Stephanie Martinez, PhD, a postdoctoral research associate at WSU’s College of Veterinary Medicine and lead author on the study. “It now appears that there could be a lot more dogs affected by this mutation—dogs from breeds that we wouldn’t have expected.”

The study found about 1 in 50 golden retrievers and 1 in 300 Labrador retrievers may have low amounts of CYP2B11. And that could have an impact on how veterinarians treat their patients: according to the American Kennel Club, Labrador retrievers are the most popular breed of dog in the US, closely followed by golden retrievers, ranked third.

The mutation also appears in mixed-breed dogs, although at a much lower prevalence—1 in 3,000.

Michael Court, BVSc, PhD, a veterinary anesthesiologist at WSU and the study’s principal investigator, has been studying slow anesthetic drug breakdown in greyhounds for more than two decades. He noted that while the profession has developed special anesthesia protocols that work very safely in greyhounds, a nagging question remained: “Should we be using these same protocols in other dog breeds?”

The researchers hope their findings can help answer that question, and they’re already taking steps in that direction: Court and Martinez are working to create a simple cheek swab test that veterinarians could use to detect the mutation and determine a dog’s sensitivity to problematic anesthetic drugs.

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