Development of UPLC-MS/MS method for the determination of colistin in plasma and kidney and its application in...

Recently, the frequent emergence of multidrug-resistant gram-negative bacterial infections has forced colistin to be used as one of the last-line options for the treatment of these infections. This study aimed to establish and validate a simple, rapid, and reliable method for the quantitative determination of colistin in plasma and kidney homogenates by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The pharmacokinetic parameters of colistin sulfate in rats and the relationship between renal accumulation and time of administration in rats were estimated by measuring plasma and renal colistin concentrations. The colistin in the sample was precipitated by acetonitrile, followed by extraction with nitrogen blow-drying and reconstitution. The chromatographic separation of analytes was conducted on an C18 column using a mobile phase consisting of 0.1% aqueous formic acid and acetonitrile. Polymyxin B was used as an internal standard (IS). Colistin and IS were monitored in positive ion mode with the following mass transition pairs: m/z 585.6→m/z 101.4 for colistin A，m/z 578.6→m/z 101.4 for colistin B and m/z 595.6→m/z 227.2 for IS, respectively. The established method expressed good linearity in 50 - 20000 ng·mL^-1 of colistin, with the lower limit of quantification (LLOQ) of 50 ng·mL^-1. Methodology validations, including accuracy, precision, matrix effect, recovery, stability, and dilution integrity met the US Food and Drug Administration (FDA) acceptance criteria for bioanalytical method validation. Noncompartmental pharmacokinetic parameters were obtained by the statistical moment theory. The estimates for the terminal half-life (t_1/2), the peak time (T_max), the peak concentration (C_max), the area under the plasma concentration-time curve (AUC_0-t), the volume of distribution (V), the total body clearance (CL) and the mean residence time (MRT_0-t) were calculated to be 2.53 ± 1.6 h, 2.17 ± 1.57 h, 2913.01 ± 644.89 ng·mL^-1, 15153.46 ± 3599.81 h·ng·mL^-1, 0.98 ± 0.56 L·kg^-1, 0.28 ± 0.09 L·h^-1·kg^-1 and 4.07 ± 1.13 h, respectively. And the concentrations of colistin in rat kidney tissue after continuous administration for 1, 3, 5, 7 days were 1.49 ± 0.35 μg·g^-1, 2.88 ± 0.74 μg·g^-1, 3.40 ± 0.25 μg·g^-1 and 4.33 ± 0.63 μg·g^-1, respectively. The established method provided a convenient, rapid, stable, sensitive, accurate way for the determination of colistin concentration, which has been successfully used for the pharmacokinetic analysis of colistin sulfate in rat and to explore the relationship between the renal accumulation of colistin and the duration of dosing.