Background and importance Patients with antibiotic allergy label (AAL) are frequent in hospitals. AAL may lead to the use of more expensive and less effective or safe alternative options.

Desensitisation is a strategy to manage AAL patients by inducing drug tolerance. Several patients receive antibiotics that are similar molecules to the one that will be desensitised later, for example, from the beta-lactam family.

Aim and objectives To analyse the percentage of patients undergoing desensitisation that were previously exposed to potentially allergy-triggering molecules.

Material and methods Retrospective study in a 400-bed university hospital from 2015 to 2021. All patients undergoing antibiotic desensitisation during this period were included.

Demographic, clinical and microbiological data were collected. Quantitative variables are presented by median and interquartile range (IQR) and univariate analysis was by Chi-square test.

Results 17 desensitisations in 14 patients: 10 women, age 74 (58–83) years, Charlson Comorbidity Index 6 (3–12), QuickSOFA score for sepsis 0.5 (0–2).

Infection focus: 4 endovascular, 4 pulmonary, 2 intra-abdominal, 2 skin and soft tissue. Ten community-acquired infections, 10 bacteraemia.

Microbiology: 6 Enterobacterales, 3 Staphylococcus spp, 2 Pseudomonas aeruginosa, 2 Streptococcus spp. Seven were polymicrobial.

Carbapenem was desensitised in 6 episodes, 5 cephalosporins, 3 penicillins. Desensitisations were completed in 15 cases. Median duration of antibiotic treatment after desensitisation was 9 (0–50) days.

Six patients were previously exposed to a similar molecule to the one that was later desensitised.

We compared both groups (‘exposed’ vs ‘not-exposed’). We found significant differences with bacteraemia (p=0.026) and the exposed group had bacteraemia more frequently.

We did not find significant differences, but tendencies with infection focus (p=0.053), endovascular focus was exposed more frequently to similar previous antibiotic; Staphylococcus (p=0.068), all patients that had staphylococcal infection were exposed to similar molecule; duration of antibiotic treatment (p=0.053), exposed group had the longest duration.

Conclusion and relevance Despite the fact that desensitisation strategy is not frequently used, many of the patients have been previously treated with antibiotics that could have triggered an allergy with clinical consequences.

Beta-lactam desensitisation in patients with bacteraemia is especially interesting due to the severity of this pathology and the high activity of this antibiotic family.

Conflict of interest No conflict of interest