Potential pitfalls in LC-MS/MS quantification of colistin for therapeutic drug monitoring of patients treated with colistimethate.

Starting from a warning of possible artificially high plasma colistin concentrations observed in clinical samples in our recently published LC-MS/MS method, we reviewed our analytical assay and demonstrated, for the first time, that caution must be paid to ionization conditions employed in the MS system. The artefact reported here demonstrates that additional experiments should be performed in the course of validation of LC-MS/MS methods to be used in samples containing both colistin and colistimethate.