Therapeutic drug monitoring of antimicrobials in a paediatric setting: A retrospective single‐centre study

Aims: Paediatric pharmacokinetics differ significantly from adults due to age-related physiological changes, necessitating precise dose adjustments. However, data on therapeutic drug monitoring (TDM) implementation in paediatric setting remain limited. This study assessed TDM use at ASST Grande Ospedale Metropolitano Niguarda, where clinical pharmacologists support therapy optimization, especially in high-intensity care settings. Methods: This retrospective study included paediatric patients (<18 years) admitted to our hospital who underwent serum drug concentration (SDC) testing for antimicrobials between 2021 and 2022. The primary objective was to describe TDM utilization, specifically the proportion of patients maintaining therapeutic SDC levels. Secondary objectives included clinical outcomes and factors linked to out-of-range SDC levels. Two TDM classifications, binary based on toxicity thresholds and expert-based, were used. Results: Among 427 SDC tests from 90 hospital stays (83 patients), median patient age was 0.2 years, and 41.1% were female. Overall, 22.0% of tests exceeded toxicity thresholds; vancomycin was most frequently monitored. The toxic group, based on binary classification, had a significantly shorter time-to-first SDC and higher rates of cardiovascular and renal comorbidities compared with the non-toxic group. Expert-based classification showed 50% not-in-range, 26.7% in-range, and 23.3% indeterminate. In-range patients had higher renal failure, CRRT use, and mortality (20.8% vs. 4.4%, p =.045), though not significant in sensitivity analyses. Kaplan–Meier curves showed no survival difference. Conclusions: TDM frequently identified out-of-range SDC, with potentially toxic levels observed in approximately one fifth of hospital stays. In this context, TDM may represent a useful tool for individualized antimicrobial dosing in complex paediatric patients.