August 4, 2022

Study shows success at disproving allergies to sulfa antibiotics

A Vanderbilt study shows that physicians can successfully identify and disprove low-risk sulfa antibiotic allergies using an oral antibiotic challenge in consenting patients prior to solid organ transplant.

Self-reported antibiotic allergies that end up in a patient’s electronic health record are common, but may lead to worse patient outcomes.

In patients who are immunocompromised, antibiotic allergies may limit options for antibiotics they must take prophylactically or therapeutically. In many cases, since alternative medications are more costly, it’s a limitation that can end up costing the patient and the health care system thousands of extra dollars each year.

A Vanderbilt University Medical Center study published in Transplant Infectious Diseases shows that physicians can successfully identify and disprove low-risk sulfa (trimethoprim/sulfamethoxazole) antibiotic allergies using an oral antibiotic challenge in consenting patients prior to solid organ transplant.

Recipients of solid organ and stem cell transplants are at higher risk of infection-related complications due to their immunocompromised status. Due to multiple factors, the transplant population is also susceptible to recurrent infections requiring antibiotics for treatment and prophylaxis.

Cosby Stone Jr., MD, MPH

“Antibiotic allergy delabeling prior to transplant is safe, is of high value and should definitely be considered in the pre-transplant evaluation period,” said Cosby Stone Jr., MD, MPH, assistant professor of Medicine in the Division of Allergy, Pulmonary and Critical Care Medicine. Stone is an author of the study that was led by Chelsea Gorsline, MD, a fellow in Transplant Infectious Diseases who recently departed VUMC after completing her fellowship.

“After a transplant, these patients will typically be taking trimethoprim/sulfamethoxazole (the most commonly prescribed sulfa antibiotic drug) to prevent infections. Being able to take the older, more effective, less expensive drug instead of the more expensive, less effective alternatives will hopefully improve their treatment outcomes and save them money for the rest of their lives.”

The retrospective analysis included 27 patients with an antibiotic allergy label who underwent evaluation for solid organ or stem cell transplantation between 2015-2020. The majority were being evaluated for lung transplants. All patients included in the review had at least one antibiotic allergy delabeled, suggesting that many self-reported antibiotic allergies were either inaccurately labeled or have stayed past their natural expiration date, Stone said.

The patients completed pre-transplant antibiotic delabeling through VUMC’s Drug Allergy Clinic and were followed for six months. There were no reported side effects within the six months, and the patients saved up to $2,910 per patient during that time, by avoiding the use of the more expensive, less effective alternative antibiotics, Stone said.

To delabel a medication allergy, a person is categorized by risk based on the story of their allergy. Those in the low-risk category can be given a single dose challenge of the antibiotic in the Drug Allergy Clinic where they can be monitored in case there’s a reaction. Those at moderate or higher risk for an ongoing allergy may be evaluated via skin testing or graded challenges (small doses prior to a dose that might be used in a typical treatment). “These are safe procedures. We do them routinely,” Stone said.

The study, which focused particularly on sulfa drug allergies due to its relevance in transplants, is part of a larger effort at VUMC looking at delabeling self-reported allergies to antibiotics, most notably penicillin, the first-line antibiotic of choice to treat infections. Over the past two years, a testing program led by Stone, Elizabeth Phillips, MD, John A. Oates Chair in Clinical Research and professor of Medicine, the Department of Pharmacy, and the Vanderbilt Learning Healthcare System, has enabled more than 100 penicillin treatments for patients who had previously been labeled as allergic to penicillin. Research shows that up to 95% of labeled penicillin allergies, reported by 10-15% of the U.S. population, may be inaccurate. The VUMC program has also looked at allergies to cephalosporin antibiotics.

The current study of allergy delabeling in transplant patients sets the stage for more research, Stone said.

“We prioritize transplant patients for antibiotic allergy evaluations because they are going to need the medications pretty soon,” he said. “Given the success shown in this small cohort, this practice could be incorporated into routine pre-transplant protocols across all our transplant teams and at other institutions,” Stone said. However, this requires knowledge of the value and the availability of the service by organ transplant teams and the availability of allergy services with relevant expertise.

“While the service is easily accessed at our institution, less than 50% of infectious disease experts have ready access to allergists who can test their patients for medication allergies,” he said.

Stone said he would like to see this study lead to collaboration with other medical centers who offer transplants.

“We’d really like to know what effect this has on the rate at which these patients get infections, which is a key indicator for transplant care,” he said. “And we’d like to know if this kind of program being available improves any of the other key outcomes for transplant patients. Above all, we’d love to collaborate with others who want to build their capacity for drug allergy delabeling. We suspect that further evidence will confirm our suspicion that bringing the first-line antibiotics back onto the table helps our patients get better outcomes and save money on their drug costs.”