High-performance liquid chromatography with fluorescence detection method for measuring colistin in human serum and its application in critically ill patients treated with colistin methanesulfonate sodium

Abstract

Colistin, in the form of colistin methanesulfonate sodium (CMS), has a narrow therapeutic window, and colistin levels must be monitored during treatment. The aim of this study was to develop and validate a high-performance liquid chromatography-fluorescence detection (HPLC-FLD) method for measuring colistin in human serum. Colistin was extracted from human serum using trichloroacetic acid and methanol for protein precipitation, followed by in-solid phase extraction derivatization with 9-fluorenylmethyl chloroformate. HPLC-FLD system using a reverse-phase HPLC C18 column and a mobile phase consisting of acetonitrile, tetrahydrofuran, and water (80%:4%:16%) were used for the quantification of colistin A, colistin B, and polymyxin B (internal standard) in human serum. The extraction recoveries were between 71% and 103%. Linear calibration curves were obtained for colistin in concentrations from 0.3 to 8.0 μg/mL, with good fit (r2 = 0.9993). The lower limit of quantitation was 0.3 μg/mL. The intra- and inter-day precision of the assay was 0.5–5% and 3.5–9.4%, respectively. The accuracy ranged from 98% to 100%. This validated method was successfully applied to the analysis of serum-receiving CMS in critically ill patients. This method will be useful to assist colistin dosage adjustment based on individual blood colistin levels for optimization of colistin therapy.