{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T23:22:51Z","timestamp":1784762571980,"version":"3.55.0"},"reference-count":33,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T00:00:00Z","timestamp":1773878400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Pharmaceutics"],"abstract":"<jats:p>Background\/Objectives: The aztreonam\/avibactam combination represents a promising therapeutic option for severe infections caused by multidrug-resistant Gram-negative pathogens, particularly in critically ill patients. Due to marked pharmacokinetic variability and the need to achieve joint pharmacokinetic\/pharmacodynamic (PK\/PD) targets of both agents, therapeutic drug monitoring (TDM) may play a pivotal role in optimizing treatment. This study aimed to develop and validate two rapid, accurate, and sensitive UHPLC\u2013qTOF MS\/MS sequential methods for quantifying aztreonam and avibactam in human plasma, suitable for routine clinical TDM. Methods: Plasma concentrations were determined by means of ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UHPLC\u2013qTOF MS\/MS), operating in positive and negative electrospray ionization modes for aztreonam and avibactam, respectively. Sample preparation consisted of protein precipitation with isotopically labeled internal standards. The method\u2019s validation was performed according to the European Medicines Agency guidelines, by assessing selectivity, linearity, precision, accuracy, recovery, matrix effects, carry-over, and stability. Clinical applicability was evaluated by reprocessing plasma samples, which were already previously collected for routine clinical practice from 20 hospitalized patients undergoing treatment with ceftazidime-avibactam plus aztreonam. Results: The methods showed excellent linearity (R2 \u2265 0.999) over ranges of 0.2\u2013100 \u00b5g\/mL for aztreonam and 0.1\u201350 \u00b5g\/mL for avibactam. Lower limits of quantification were 0.2 \u00b5g\/mL and 0.1 \u00b5g\/mL, respectively. Intra- and inter-day precision and accuracy met the EMA criteria at all of the quality control levels. Extraction recovery exceeded 90% for both analytes, and matrix effects were effectively compensated by internal standards. Stability testing highlighted the need for careful sample handling, particularly for aztreonam under repeated freeze\u2013thaw conditions. Clinical application revealed substantial inter-individual variability in steady-state concentrations. Conclusions: The validated UHPLC\u2013qTOF MS\/MS assays provide robust and sensitive sequential quantification of aztreonam and avibactam in human plasma, supporting TDM-guided dose optimization in clinical practice.<\/jats:p>","DOI":"10.3390\/pharmaceutics18030377","type":"journal-article","created":{"date-parts":[[2026,3,19]],"date-time":"2026-03-19T08:54:37Z","timestamp":1773910477000},"page":"377","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Accurate and Sensitive UHPLC\u2013Tandem Mass Spectrometry Sequential Methods for Therapeutic Drug Monitoring of Aztreonam\/Avibactam in Human Plasma"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0009-0006-9807-4500","authenticated-orcid":false,"given":"Ilaria","family":"Trozzi","sequence":"first","affiliation":[{"name":"Clinical Pharmacology Unit, Department for Integrated Infectious Risk Management, IRCCS Azienda Ospedaliero-Universitaria di Bologna, 40138 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0004-8784-9070","authenticated-orcid":false,"given":"Beatrice","family":"Giorgi","sequence":"additional","affiliation":[{"name":"Clinical Pharmacology Unit, Department for Integrated Infectious Risk Management, IRCCS Azienda Ospedaliero-Universitaria di Bologna, 40138 Bologna, Italy"},{"name":"Specialization School of Clinical Pharmacology and Toxicology, Alma Mater Studiorum Universit\u00e0 di Bologna, 40138 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-6856-8936","authenticated-orcid":false,"given":"Riccardo","family":"De Paola","sequence":"additional","affiliation":[{"name":"Clinical Pharmacology Unit, Department for Integrated Infectious Risk Management, IRCCS Azienda Ospedaliero-Universitaria di Bologna, 40138 Bologna, Italy"},{"name":"Specialization School of Clinical Pharmacology and Toxicology, Alma Mater Studiorum Universit\u00e0 di Bologna, 40138 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3018-3779","authenticated-orcid":false,"given":"Milo","family":"Gatti","sequence":"additional","affiliation":[{"name":"Clinical Pharmacology Unit, Department for Integrated Infectious Risk Management, IRCCS Azienda Ospedaliero-Universitaria di Bologna, 40138 Bologna, Italy"},{"name":"Department of Medical and Surgical Sciences, Alma Mater Studiorum University of Bologna, 40138 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6966-7167","authenticated-orcid":false,"given":"Federico","family":"Pea","sequence":"additional","affiliation":[{"name":"Clinical Pharmacology Unit, Department for Integrated Infectious Risk Management, IRCCS Azienda Ospedaliero-Universitaria di Bologna, 40138 Bologna, Italy"},{"name":"Department of Medical and Surgical Sciences, Alma Mater Studiorum University of Bologna, 40138 Bologna, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,19]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2059","DOI":"10.1093\/cid\/ciad100","article-title":"Mortality Attributable to Bloodstream Infections Caused by Different Carbapenem-Resistant Gram-Negative Bacilli: Results from a Nationwide Study in Italy (ALARICO Network)","volume":"76","author":"Falcone","year":"2023","journal-title":"Clin. 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