4CPS-236 Assessment of therapeutic drug monitoring in adult cystic fibrosis patients on outpatient parenteral antimicrobial therapy

<h3>Background and Importance</h3> Outpatient parenteral antimicrobial treatment (OPAT) is an alternative to inpatient care in selected patients, particularly those who require repeated treatments, such as adults with cystic fibrosis (CF). Standard treatment for these patients includes aminoglycosides, linezolid, voriconazole and teicoplanin. Due to drug-associated toxicity risk, proactive therapeutic drug monitoring (TDM) can be valuable for dosing adjustment to optimise effectiveness and minimise toxicity. <h3>Aim and Objectives</h3> To establish how many OPAT episodes are submitted to TDM out of the total that could benefit from it. Additionally, to analyse the alteration of the analytical variables due to antimicrobial toxicity. <h3>Material and Methods</h3> Retrospective, single-centre study including adult patients (&gt;18 years) with CF diagnosis on OPAT from January 2019 to December 2023. Demographic, clinical, analytical, OPAT episode outcome and TDM variables were collected. <h3>Results</h3> The study included 64 patients, 33 women (51.6%), with a mean age of 31.5 (±9.80) years at the onset of the episode. The median treatment duration was 21 days (IQR:15.0–23.0). A total of 236 episodes were analysed, of which 160 (67.8%) could benefit from TDM, however only six episodes (3.7%) received it. Aminoglycosides were involved in 148 episodes, among which only five (3.4%) were monitored; voriconazole in one which was subjected to TDM; teicoplanin in eight and linezolid in three, none of which underwent TDM. Of the six episodes that underwent TDM, four (66.7%) had values out-of-range in the first determination. Regarding the outcome of the 160 episodes, 18 (11.2%) were prematurely discontinued, none of which received TDM. Most of the remaining episodes resolved the infectious process (97 (60.6%) episodes) or were switched to oral therapy (35 (21.9%) episodes). Regarding potential antimicrobial toxicity, blood test results during the OPAT episode were available for 43 (26.9%) episodes, with 10 (23.3%) showing altered analytical values. Renal function was impaired along three episodes treated with aminoglycosides and hepatic alterations occurred during one episode treated with teicoplanin. Among the altered, none of them underwent TDM. <h3>Conclusion and Relevance</h3> Few OPAT episodes undergo TDM, and most show out-of-range values. Analytical variables are rarely monitored, and if so, altered values potentially linked to the antimicrobial are seen. Thus, increasing TDM in OPAT episodes could help to optimise treatment and reduce toxicity risks. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest