By Holly Richards/University of Illinois College of Veterinary Medicine
At nearly every visit to a doctor, people are asked whether they have drug allergies. This is because allergic reactions to medications can be debilitating and even life-threatening. Pets also can have drug allergies, although research and education in this area is less well-developed than in the human medical field.
Dr. Sidonie Lavergne, a faculty member at the University of Illinois College of Veterinary Medicine, is an expert in veterinary pharmacology, toxicology and the immune system. She is concerned that a lack of awareness of drug hypersensitivity reactions in the veterinary field has led to an underestimation of the severity and frequency of these reactions. For this reason, she is spearheading an investigation into the nature and occurrence of allergic events, focusing on both dogs and humans.
"There really are no physiological differences between humans and pets as far as drug allergies go," Lavergne said. "Animals probably have just as many reactions as people do."
She said, as veterinary schools begin to include in their curricula this new knowledge about drug allergies in animals, it's likely that drug reactions that had previously been misdiagnosed will more frequently be recognized and reported.
In both humans and pet species, allergic reactions can manifest in a variety of ways. Lavergne mentioned dermatological conditions (from a mild rash to life-threatening massive skin detachment), but also blood abnormalities (such as abnormal bleeding or decreased immune defenses) and liver damage, to name just a few.
An immediate allergic reaction, occurring within hours of exposure, is known as anaphylaxis. According to Lavergne, most drug allergic reactions are not immediate but rather require days, sometimes months, of drug exposure before onset. Although anaphylactic events get more attention because they take place close to the drug exposure and are often clinically impressive, she cautions that delayed reactions can be just as dangerous.
"Delayed hypersensitivity reactions can lead to the patient's death," she said. "They can also delay recovery from the treated illness, sometimes leaving the patient with long-term adverse health effects. These reactions prevent the veterinarian from ever using this drug again in the patient, which can be problematic in treating infections that are sensitive to only a very few antibiotics, for instance."
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.
"One of the big issues is that we do not know why the immune system suddenly decides to attack a drug. Veterinary researchers have not had access to patients with a history of drug allergy because for so long the problem has gone undiagnosed or dismissed as not important," Lavergne said.
She 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.
And thanks to her extensive background in the field, she is able to provide free consultation to veterinarians, whether they need help managing a patient with a life-threatening reaction or they are not certain that their patient had a drug allergic reaction.
Lavergne provides testing of samples for veterinarians not only to help treat current patients with signs of potential reactions but also to re-evaluate 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, she said. "And if the animal was on multiple drugs at the time, I can determine which one is likely to have caused the problem.
"Any clinician with even the slightest suspicion that they've encountered a patient with a drug allergy is apt to benefit by giving me a call and/or sending me a sample from the patient."
In fact, Lavergne has already been able to help a number of veterinarians diagnose and appropriately treat some very serious conditions through phone consultations. Not only does this collaboration help the patients that are experiencing the problem, but every sample that she receives adds to the knowledge base she is establishing with her research and is bound to benefit allergic pets in the future.
And, as the field of veterinary medicine continues to expand its use of therapeutic prescription medications in pets, often with multiple drugs being used at the same time and for long periods of time, the relevance of Lavergne's research will become evident to more and more pet owners.
"I suspect that as the veterinary community becomes more attentive to the signs and the prevalence of drug allergies," she said, "owners will soon be asked about their pets' allergies during their veterinary appointments just as often as human patients are now."
An archive of pet columns from the UI College of Veterinary Medicine is available at http://vetmed.illinois.edu/petcolumns/ . Requests for reprints of this article may be directed to Chris Beuoy, firstname.lastname@example.org.