Background and Importance Linezolid is an antibiotic that presents high inter- and intra-individual variability and therefore may compromise its clinical efficacy or increase the risk of associated toxicity.

Aim and Objectives To establish a programme for monitoring linezolid plasma levels that will allow us to proactively identify patients who can benefit most from its use and to evaluate its results in our centre.

Material and Methods A literature review was performed to define the criteria that allowed us to identify patients who were candidates for pharmacokinetic monitoring of linezolid.

We established the determination of plasma concentrations before the administration of the 5th dose and then periodically every 3-4 days until the end of treatment. The efficacy and safety criterion was to maintain the trough plasma concentration (Cmin) in the therapeutic range (between 2 and 8 mg/L).

Results The criteria selected for the identification of patients who were candidates to be part of the monitoring programme were: critical patients, transplanted patients, severe burns or cystic fibrosis, obese patients (BMI > 30), kidney failure (creatinine clearance < 30 ml/min) and liver failure (Child Pugh C), renal replacement therapies, prolonged treatments (> 3 weeks) and treatment with Glycoprotein-P inducers.

From January to April 2022, a total of 20 patients that met at least one of the aforementioned criteria were included in the programme . All patients started treatment in critical care units and the chosen route of administration was intravenous. Eighty-five percent of the patients were men, the median age was 69 years and the mean duration of treatment was 11.6 days.

A total of 50 samples were analysed (2.5 samples per patient). The mean Cmin was 5.3 mg/L. Thirty samples (60%) were out of therapeutic range.

Fifty pharmacokinetic reports were performed. In 60% of the cases, modifications of the dosing regimen were made: 17 were dose increases and 13 were dose decreases.

Conclusion and Relevance Incorporating this programme into clinical practice allows us to proactively identify the patients who could benefit most from linezolid monitoring.

The results demonstrate the high variability of linezolid plasma levels and the usefulness of dosing recommendations issued by the Pharmacy service to ensure that the Cmin remains within the therapeutic range.

Conflict of Interest No conflict of interest