Grand RoundsOptimization of Aztreonam in Combination With Ceftazidime/Avibactam in a Cystic Fibrosis Patient With Chronic Stenotrophomonas maltophilia Pneumonia Using Therapeutic Drug Monitoring: A Case StudyCowart, Mallory C. PharmD, MBA, BCPPS; Ferguson, Chelsea L. PharmD, BCPPSAuthor Information Department of Pharmacy, Orlando Health Arnold Palmer Hospital for Children, Orlando, Florida. Correspondence: Chelsea L. Ferguson, PharmD, BCPPS, Orlando Health Arnold Palmer Hospital for Children , 92 W. Miller St, MP 349 Orlando, FL 32806 (e-mail: [email protected]). The authors declare no conflict of interest. Therapeutic Drug Monitoring: April 2021 - Volume 43 - Issue 2 - p 146-149 doi: 10.1097/FTD.0000000000000857 Buy Metrics Abstract In this clinician-therapeutic drug monitoring (TDM) consultant interaction, the authors describe the use of TDM in an 11-year-old female patient with cystic fibrosis receiving ceftazidime/avibactam and aztreonam for the treatment of persistent pulmonary exacerbations caused by Stenotrophomonas pneumonia. Serum drug concentrations at a steady state confirmed inadequate antimicrobial exposure, and continuous infusions of both ceftazidime/avibactam and aztreonam were required to optimize the percentage of time when free drug remained above the minimum inhibitory concentration (MIC), known as fT > MIC. After dose adjustment, this continuous infusion strategy resulted in 100% target attainment for fT > MIC. This case illustrates the importance of TDM, and the logistical issues encountered with the use of alternative dosing strategies in pediatric patients with CF. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.