Automated magnetic bead‑based LC-Triple Quadrupole MS approach for sensitive colistin therapeutic drug monitoring in human plasma

Colistin, a cationic peptide antibiotic produced by Bacillus polymyxa subsp. colistinus, is a last-line defense against multidrug-resistant Gram-negative bacteria. However, its clinical utility is hampered by significant nephrotoxicity and neurotoxicity at supratherapeutic levels and the risk of promoting antimicrobial resistance (AMR) at subtherapeutic concentrations. To enable precise therapeutic drug monitoring (TDM) and mitigate these risks, we developed a fully automated magnetic bead-based LC-Triple Quadrupole MS method for sensitive quantification of colistin in human plasma. The method utilizes hydrophilic-lipophilic balance (HLB) magnetic beads coupled with an automated 96-well extraction system. Colistin A, colistin B, and the internal standard (polymyxin B1) were analyzed via LC-Triple Quadrupole MS employing positive electrospray ionization. Method validation was performed in accordance with FDA guidance. The method exhibited excellent linearity, sensitivity, precision, accuracy, recovery, and minimal matrix effects. The assay demonstrated the broadest quantifiable range reported to date (0.01-20 µg/mL) for colistin A and B in a 5.0-min runtime. The lower limit of quantification (LLOQ) was 0.01 µg/mL, ensuring high sensitivity and specificity with negligible endogenous interference. This automated, cost-effective, and robust platform facilitates reliable colistin TDM, supporting personalized dosing strategies to optimize efficacy and minimize toxicity.