Drug Allergies More Common in Patients with CSU, Study Finds

October 22, 2020
Jared Kaltwasser

Drugs often trigger outbreaks of hives, but investigators observed no clear evidence as to the overall incidence of drug allergies in CSU.

Patients with chronic spontaneous urticaria (CSU) tend to have higher rates of self-reported drug allergies compared to the general population, according to a new study.

Corresponding author Merritt L. Fajt, MD, of the University of Pittsburgh School of Medicine, and colleagues, wrote that CSU is generally associated with recurrent hives that do not have a clear trigger.

Sometimes, drugs appear to be at play in triggering outbreaks of hives, but the authors said there’s no clear evidence as to the overall incidence of drug allergies in CSU.

Fajt and colleagues suspected that drug allergies would be higher in patients with CSU, and so they constructed a study to assess allergy rates based on self reports.

The investigators identified 362 patients with CSU who had sought care at a university allergy and asthma clinic over a 10-year period, from 2007 to 2017. Patients were categorized based on their reported drug allergies or the lack thereof.

They were also analyzed in terms of single- and multiple-drug allergies. For the purposes of the study, “multiple” drug allergies was defined as having allergies to 2 or more drugs that were not chemically related.

A majority of the patients in the study (56%) reported a drug allergy. The most commonly reported allergy was a penicillin allergy, an allergy whose most frequently reported symptom was urticaria, the authors said.

Demographically, patients were more likely to report a drug allergy if they were white, older, or had a high body mass index (BMI). However, when it came to multiple drug allergies, the 115 patients who reported them were more likely to be female. Older age, white race, and co-existing asthma were also linked with a higher likelihood of multiple drug allergies. A total of 29% of patients in the study reported asthma.

The data showed that the rate of drug allergies in patients with CSU is substantially higher than that of the general population, where rates of drug allergies are estimated at between 5-25%.

The finding that penicillin was the most common drug allergy aligns with earlier research. Sixty-six patients (18%) reported having a penicillin allergy. A 2015 study examining the prevalence of penicillin allergies specifically in patients with chronic urticaria found the rate of allergy was approximately 3 times higher in the urticaria population compared with the general population.

In the current study, penicillin allergies were also linked with a higher risk of multiple drug allergies. Of CSU patients with a penicillin allergy, 68% said they also had other drug allergies.

Still, Fajt and colleagues said it can be difficult to know the true rate of drug allergies in this population, given the self-reported nature of the data. The authors said it can also be difficult to get patients to cease taking antihistamines in order to conclusively confirm an allergy through skin testing and challenge.

The investigators also cautioned that, in addition to misdiagnosis of drug allergies, it was also possible that patients in this cohort have a misdiagnosis of asthma, which can be confused with vocal cord dysfunction (VCD).

In their conclusion, the authors said their data suggest drug allergies are a significant problem for patients with CSU. They said physicians treating patients with CSU should take careful histories of patient drug allergies and asthma, if applicable.

They added that further study is warranted to avoid the potential for morbidity associated with less efficacious and costlier drugs.

The study, "Factors Associated with Self-Reported Drug Allergies in a Large Chronic Spontaneous Urticaria Cohort," was published online in Current Drug Safety.