The PALACE study, an international research endeavour, has evaluated a safer and simpler approach to penicillin allergy testing

Penicillin allergy is a widespread public health concern, with one in 10 patients being documented as having a penicillin allergy. Those patients are more likely to be prescribed alternative antibiotics that are often less effective against certain infections. This can lead to treatment failure, increased risks of antibiotic resistance and the development of superbugs. Yet, fewer than 5% of patients labelled with a penicillin allergy are truly allergic.

Undertaken by a team of researchers from six specialized centres in Canada, the U.S. and Australia, the PALACE study has sought to address these issues by evaluating a new approach to identifying low-risk penicillin allergy patients and to determining the best way to test and treat them. The results of this clinical trial, published in JAMA Internal Medicine, pave the way for the adoption of a simple oral test called “direct oral penicillin challenge” as a safe and effective alternative to traditional skin testing, which is labour-intensive and not easily accessible to all, as well as being time-consuming and painful for the patients.

“The biggest takeaway from the PALACE study is that patients with a low-risk penicillin allergy, like a childhood rash, can safely have a test dose of penicillin to determine if they are still allergic. This will change the way doctors test for penicillin allergy in the future. Millions of patients worldwide, including millions of Canadians, will be able to have their penicillin allergy disproved by a safe single oral test dose following a carefully risk-validated risk assessment,” says Dr. Ana-Maria Copaescu , who is first author of the study, associate investigator in the Infectious Diseases and Immunity in Global Health Program at the Research Institute of the McGill University Health Centre (RI-MUHC), and the leading investigator for the North American sites.

“The PALACE study is the first international randomized study to look at reducing the burden of penicillin allergy by seeing if a simple test dose procedure following careful assessment can be used to disprove a patient penicillin allergy, rather than traditional skin or scratch testing,” adds Prof. Jason Trubiano, senior author of the study, director of Infectious Diseases and head of the Centre for Antibiotic Allergy and Research at Austin Health in Australia. “With this new procedure, we can give back a lifesaving antibiotic, penicillin, to more than 90 per cent of patients that undergo testing.”

Towards a change of practice

The study enrolled 382 adults who were assessed using a specialized risk assessment tool called PEN-FAST. Participants were randomly assigned to receive either a direct oral penicillin challenge or the standard approach, which involves penicillin skin testing followed by an oral challenge. The primary goal was to determine if the direct oral penicillin challenge was as effective as the standard method for removing the allergy label.

The study found that only one patient (0.5 %) in each group experienced a positive reaction to the penicillin challenge. This demonstrates that the direct oral penicillin challenge is just as effective as the standard method. Importantly, there were no significant differences in adverse events between the two groups, and no serious adverse events were reported.

These findings have wide-ranging implications for patient care. By quickly, safely and accurately identifying and testing low-risk penicillin allergy patients, healthcare providers can ensure appropriate antibiotic prescriptions.

A solution to a multifaceted problem

Research has shown that 80 per cent of people who have had a penicillin allergy for over ten years eventually lose their sensitivity to the medication. Yet many adult patients carry a penicillin allergy label from childhood.

“A penicillin allergy label can appear from multiple sources, such as avoidance as a result of family history or non-allergic mild side effects such as headache or stomach pain, skin rashes associated with viral infections in kids that are subsequently labelled as allergic, fear of the drug, etc.,” says Dr. Copaescu, who is also an assistant professor in the Department of Medicine at McGill University. “And for various reasons, unverified penicillin allergy labels are not often challenged. As a result, many patients receive broad-spectrum alternative antibiotics associated with increased healthcare cost and increased antibiotic resistance, and in some cases, higher rates of treatment failure, medication errors and undesirable side effects or complications.”

The PALACE study represents a major advancement in addressing the global issue of penicillin allergies, with the potential of making penicillin delabeling more universally available.

“The current procedure to verify or delabel a penicillin allergy requires a specialized skill set and uses costly specialized testing reagents in an allergist’s office. If infectious disease specialists, general internists or general practitioners could delabel low-risk patients through direct oral challenge, this would significantly increase the number of patients who could be safely delabeled and significantly reduce the global burden of penicillin allergy,” adds Dr. Copaescu.

About the study

The article Efficacy of a clinical decision rule to enable direct oral challenge in patients with low-risk penicillin allergy – The PALACE Randomized clinical Trial is published in JAMA Internal Medicine

DOI :10.1001/jamainternmed.2023.2986

Dr. Copaescu wishes to thank the Montreal General Foundation and the RI-MUHC for their support.