Veterinary expert digs into drug allergies in pets

When an animal doesn't respond to an antibiotic—or its condition worsens when placed on the drug—it's easy to blame antibiotic resistance. But is that catchall explanation really the most likely possibility for treatment failure?

Not necessarily, says Sidonie Lavergne, DVM, PhD, assistant professor of pharmacology at the University of Illinois College of Veterinary Medicine. In fact, it could be an adverse reaction to the drug. Lavergne believes that drug hypersensitivities are probably much more common than most veterinarians are trained to recognize, and to raise awareness, she's spearheading a research effort to better understand and identify these types of reactions in dogs, primarily focusing on delayed allergic reactions that target the skin.

"When drugs are given to pets, either orally or injected, the number one organ that's affected is the skin," says Lavergne. "My laboratory is trying to understand why."

Lavergne explains that allergic reactions to drugs can manifest in a variety of ways—from dermatologic conditions, such as rashes, to blood abnormalities and liver damage. And while the more easily identifiable anaphylactic reactions occur within hours of exposure to an allergen, most drug reactions are delayed and can take months of drug exposure before clinical signs are evident. This makes it even more likely that veterinarians won't realize they're dealing with a drug allergy.

Lack of training, awareness

One reason adverse drug reactions aren't on most veterinarians' rule-out lists is they haven't been trained to consider it as an option. "Most veterinary curricula don't include adverse drug events in their courses," says Lavergne. "If students aren't trained to be aware of it, it probably won't be on their radar."

Lavergne points out that clinicians and professors in veterinary schools need to be convinced that drug hypersensitivities are an issue and bring it to the curriculum in pharmacology or toxicology courses.

"Once veterinarians become aware of these adverse drug events, they would realize it happens more often in animals than we think," Lavergne says.

Building a knowledge base

Lavergne's laboratory is currently conducting research in this area and can test animal blood samples for the presence of immune markers, specifically memory T cells and antibodies, to determine what drug could be responsible for an adverse reaction. These diagnostic services, as well as sample supplies and shipping costs, are available to practitioners at no charge. Lavergne also provides free phone consultations to veterinarians and can help them refine their diagnosis—even if a suspected adverse event happened in the past.

"Even if the event happened years ago, a dog will have memory immune cells in its blood that can help confirm whether there was an allergic reaction," Lavergne says. "And if the animal was on multiple drugs at the time, I can determine which one is likely to have caused the problem."

Lavergne believes that not only will this diagnostic service help veterinarians treat patients currently experiencing an adverse drug reaction, but that the knowledge obtained through her research efforts will aid allergic pets in the future.

"I suspect that as the veterinary community becomes more attentive to the signs and prevalence of drug allergies, owners will soon be asked about their pets' allergies during their veterinary appointments just as often as human patients are now," Lavergne says.

Lavergne can be reached at the University of Illinois College of Veterinary Medicine by phone, (217) 265-0315, or via her email at slavergn@illinois.edu.