I’ve just noticed a big difference in the way in which drugs are prescribed for people and pets. Whenever I am prescribed a medication, invariably both the doctor and the pharmacist will ask about potential allergies to the drug in question, but I’ve never done the same myself as a veterinarian (and I’m often both the doctor and the pharmacist).

Why is that?

First of all, I’d have to say that the scariest type of drug allergy (anaphylaxis) is quite rare in pets. Anaphylaxis (or anaphylactic shock) can cause difficulty breathing, low blood pressure, collapse, and death when not quickly addressed. I’ve had several patients develop anaphylaxis after vaccination, but I can’t recall a single case associated with medication administration.

That’s not to say that adverse drug reactions don’t occur in animals; it’s just that the problems that do arise tend to be less dramatic than those seen with anaphylaxis and can pop up a relatively long time after the medication is given.

Possible symptoms of drug allergy in pets include facial swelling, hives, itchy skin, respiratory changes, lethargy, depression, vomiting, diarrhea, loss of appetite, altered urinary habits, and abnormal bleeding. These types of clinical signs may or may not be associated with drug therapy, but they should always be brought to a veterinarian’s attention.

Secondly, drug allergies simply aren’t at the top of (or even on) many doctor’s rule-out lists when presented with a dog with the aforementioned symptoms due to a lack of readily available information and training. Owners have asked me whether or not something they are observing in their pet could be a side effect of a drug they are giving, and unless it is a problem that is well-recognized, I’m usually left answering, “Anything is possible.”

The University of Illinois’s College of Veterinary Medicine is now offering a laboratory test that can do a better job of answering that question. According to an article on their website:

The body’s immune system uses a type of cell called a “memory T cell” to keep track of foreign invaders, such as viruses and bacteria. Memory T cells, after being exposed to a vaccine, will later mount a protective attack if the associated pathogen is encountered again. These same protective cells have the ability to recognize and attack substances that have caused allergic reactions in the past, which is why a patient can never be re-exposed to a drug once an allergy to it has developed.

Dr. [Sidonie] Lavergne can test for the presence of drug-specific memory T cells and small molecules recognizing the drug (antibodies) in a pet’s blood sample. Her laboratory tests patients’ blood for diagnostic purposes free of charge. All supplies and shipping costs are also covered by her research project.

Dr. Lavergne provides testing of samples for veterinarians not only to help treat current patients with signs of potential reactions but also to reevaluate past cases in which conditions were unexplained and the diagnosis of drug allergy was never confirmed.

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

Pretty neat stuff. Whenever a pet is on medication(s), everyone involved in that animal’s care should be on the lookout for unexpected health problems. Consider asking your vet to send a blood sample to Dr. Lavergne’s lab for confirmation if anything out of the ordinary develops.

Dr. Jennifer Coates

Image: Denys Kurbatov / Shutterstock