Optimization of Aztreonam in Combination With Ceftazidime/Avibactam in a Cystic Fibrosis Patient With Chronic Stenotrophomonas maltophilia Pneumonia Using Therapeutic Drug Monitoring: A Case Study.

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.