Antibiotic allergies are prevalent in elderly patients yet a large number are not genuine, Melbourne researchers report.

This inappropriate labelling is likely fuelling inappropriate prescribing of broad-spectrum antibiotics that are restricted by antimicrobial stewardship programs, say the research team led by Dr Jason Trubiano from Austin Health in Melbourne.

Published in this week’s MJA the study involving 453 inpatients found almost a quarter had an antibiotic allergy label (AAL), of which 34% were related to simple penicillins, 13% to sulphur antimicrobials, and 11% to cephalosporins.

However many of these “allergies” were really side- effects or intolerances, or patients were defined as “low risk phenotypes”.

These patients were significantly more likely to be treated with broad-spectrum antibiotics such as ceftriaxone and fluoroquinolones usually restricted by antimicrobial stewardship programs.

“To understand the high prevalence of antibiotic allergy labels and the predominance of low-risk phenotypes in our study group requires an understanding of ‘penicillin past’, as many antibiotic allergy labels are confounded by the impurity of early penicillin formulations and later penicillin contamination of cephalosporin products,” the research team wrote.

They also found that 8 of the 107 patients with an AAL had previously received an antibiotic from the class to which they were believed allergic but none had experienced an adverse event.

“If patients had received and tolerated an antibiotic to which they were previously considered allergic, they were more likely to accept a hypothetical re-challenge than those who had not.”

Educating clinicians and making changes in the recording of adverse drug reactions by hospitals is required to ensure the accuracy of AALs, the researchers concluded.