Some Dog Breeds Could Be at Risk of Adverse Drug Reactions

Analysis by Dr. Karen Shaw Becker

dog anesthesia recovery

Story at-a-glance -

  • Some greyhounds have less CYP2B11, an enzyme that breaks down certain medications, leaving the dogs at risk of potentially life-threatening adverse reactions during recovery from anesthesia
  • When researchers surveyed DNA from 63 dog breeds, it revealed that some popular breeds, including golden retrievers and Labrador retrievers, may also have difficulty breaking down common anesthetics
  • Among golden retrievers, about 1 in 50 may be at risk, along with about 1 in 300 Labrador retrievers; mixed breeds could also be affected, with about 1 in 3,000 potentially at risk
  • Researchers are in the process of creating a cheek swab test that could be used by dog owners and veterinarians to reveal dogs with the mutation
  • Not all dogs respond to anesthesia the same, so ask your veterinarian what their individualized anesthetic protocols are for your specific breed

It’s been known for years that certain greyhounds may have a genetic mutation that makes them susceptible to adverse effects from anesthesia. The mutation causes less CYP2B11, an enzyme that breaks down certain medications, leaving the dogs at risk of potentially life-threatening adverse reactions during recovery from anesthesia.

Dog breeds closely related to greyhounds, including whippets, borzois, Italian greyhounds and Scottish deerhounds, are also at risk of the mutation, but researchers at Washington State University’s (WSU) College of Veterinary Medicine conducted a study on 63 other dog breeds to determine if they also had an increased risk1 — and the results were surprising.

Certain Golden and Labrador Retrievers at Risk

While differences in drug responses have been extensively studied in humans, the same isn’t true in dog breeds. Greyhounds and other sighthounds are known to recover more slowly from certain anesthetics drugs, including several thiobarbiturates (thiopental and thiamylal) and propofol, than other breeds, but researchers wondered if other dog breeds might be affected as well.

Initially, greyhounds were thought to be sensitive to anesthesia due to their naturally low body fat content. But the WSU researchers later determined a deficiency in CYP2B11 to be the cause.

Using donated samples from the WSU Veterinary Teaching Hospital DNA Bank, they then extended their survey to 63 dog breeds, which revealed that some popular breeds, including golden retrievers and Labrador retrievers, may also have difficulty breaking down common anesthetics.

“We started with a condition we thought was specific to greyhounds and affected a relatively small number of dogs,” lead study author Stephanie Martinez, WSU postdoctoral research associate, said in a news release. “It now appears that there could be a lot more dogs affected by this mutation — dogs from breeds that we wouldn’t have expected.”2

Among golden retrievers, about 1 in 50 may be at risk, along with about 1 in 300 Labrador retrievers. Mixed breeds could also be affected, with about 1 in 3,000 potentially at risk.

“While the mutation is not that common in most breeds — outside of greyhounds and other related breeds — because some of these other breeds are so popular, a relatively large number of dogs in this country could be affected.” Martinez said.3 According to the study, this is particularly true for Labrador retrievers, golden retrievers and English bulldogs:

“In addition to detecting CYP2B11-H3 in 9 Sighthound breeds (other than Greyhounds), we also found this haplotype in 10 non-Sighthound breeds suggesting that the Sighthound CYP2B11 poor metabolizer phenotype might be found in non-Sighthound breeds. For most of these non-Sighthound breeds, the H3 haplotype frequency was relatively low (less than 10%).

Therefore, the predicted frequency of the poor metabolizer CYP2B11 H3/H3 diplotype would be less than 1% … However, we note that three of the breeds, including Labrador Retriever, Golden Retriever, and English Bulldog were ranked by the AKC in 2018 as the first, third, and fifth most popular dog breeds owned in the USA, respectively, based on annual AKC registration.

Consequently, the overall impact of this gene variant on these breeds could be substantial, at least in terms of the absolute numbers of dogs affected.”4

Other Drugs May Also Be Dangerous for Dogs With the Mutation

Special anesthesia protocols exist for greyhounds, and the researchers questioned whether such protocols should be used for other dog breeds as well. They suspect that dogs with the mutation may have trouble breaking down not only anesthetic drugs, but other drugs as well.

“The challenge now is to provide accurate advice to veterinarians on what drugs and drug dosages should be used in affected patients,” veterinary anesthesiologist and study author Michael Court said.5

To determine which dogs may be at risk, other than greyhounds and related breeds, the researchers are in the process of creating a cheek swab test that could be used by dog owners and veterinarians to reveal dogs with the mutation.

General Anesthesia Guidelines for Dogs

Aside from greyhounds and other dogs with a deficiency in CYP2B11, other dogs may also be at increased risk from general anesthesia. This includes pets with heart disease, diabetes, hypothyroidism, Cushing’s disease or Addison’s disease, as well as obese animals and those suffering from liver or kidney disease.

Certain breeds also have increased responsiveness to anesthesia, which means it takes less of the drug to produce the desired effect, which increases the risk for overdose. Others, namely brachycephalic dogs (breeds with pushed in faces, such as the Boxer), have a higher risk for airway obstruction, compared to breeds with longer muzzles.

Other breeds that need careful attention during anesthesia include herding breeds like the collie, which have a genetic mutation in the ABCB1 gene that allows certain drugs to accumulate in the brain — including some anesthesia agents. Toy breeds, giant breeds and Doberman pinschers, which have a genetic variation that can cause von Willebrand disease, a problem with blood clotting, also need special attention.

Because not all dogs respond to anesthesia the same, a pre-anesthetic evaluation should be performed to identify individual risk factors that could influence your dog’s ability to tolerate anesthesia. The pet must also be appropriately monitored — beginning with premedication and continuing to extubation — throughout the procedure.

If you’re unsure about your dog’s risk of adverse effects to anesthesia or any drug, be sure to ask your veterinarian, who should be able to customize an individualized protocol for your dog.