Chromatography and mass spectrometry in therapeutic drug monitoring: Method performance, practical trade-offs, and...

Therapeutic drug monitoring (TDM) is an essential clinical tool to individualize dosing for medications with narrow therapeutic indices or highly variable pharmacokinetics. This review provides a comprehensive overview of chromatography and mass spectrometry-based methodologies for TDM, focusing on their application to antibiotics (especially β-lactams), immunosuppressants, antifungals, and antiepileptic drugs in adult, pediatric, and intensive care settings. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has emerged as the gold-standard analytical technique for many TDM assays due to its superior sensitivity and specificity. LC-MS/MS methods enable simultaneous quantification of multiple drugs with minimal interference, which is particularly advantageous for patients on multi-drug regimens. Conventional chromatographic methods (HPLC with UV or fluorescence detection) remain in use as cost-effective alternatives for certain high-concentration drugs, while automated immunoassays are widely used for their high throughput and ease of use despite issues of cross-reactivity and limited availability for newer drugs. We compare the analytical performance of these methodologies, including sensitivity, specificity, accuracy and precision, matrix effects, and sample throughput. We also discuss practical aspects of clinical implementation: instrument and reagent costs, requirement for specialized personnel and validation and operational challenges such as turnaround time in critical care. In conclusion, chromatography and mass spectrometry techniques offer unparalleled analytical performance for TDM, addressing limitations of immunoassays and enabling precise drug management in complex clinical scenarios. This review underscores the importance of these methods in optimizing therapy for critical drug classes and highlights the ongoing innovations bridging the gap between research laboratories and real-world clinical practice.