Polymyxin B1

Two liquid chromatographic-tandem mass spectrometric (LC-MS/MS) methods have been developed and validated for the quantitative determination of polymyxin B1, polymyxin B2 and polymyxin B1-1 concentrations in human plasma and treated urine. During method development, technical challenges such as the separation of structural isomers polymyxin B1and polymyxin B1-1 and nonspecific binding in urine samples were encountered and overcome. Two automated solid phase extraction methods were used to extract plasma samples (100μL) and urine samples (200μL) and the resulting extracts were analyzed using reversed phase LC-MS/MS with an electrospray (ESI) interface and selected reaction monitoring (SRM) in the positive ionization mode. Both methods were validated over a calibration curve range of 5.00-2000ng/mL with a linear regression and 1/x(2) weighting. The between-run relative standard deviation (%RSD) ranged from 4.5 to 9.5% for the plasma assay and from 1.1 to 7.1% for the urine assay. For the plasma assay, the between-run accuracy ranged from 100.5 to 115.2% of nominal at all QC concentrations including the LLOQ. For the urine assay, the between-run accuracy ranged from 92.0 to 106% of nominal at all QC concentrations including the LLOQ. The extraction recoveries for all polymyxins in both assays were between 54.0 and 64.2%. Long term matrix storage stability for all polymyxins was established at both -20°C and -70°C for up to 85 days in human plasma and for up to 55 days in treated human urine. Both assays were used for the measurement of polymyxin B1, polymyxin B2 and polymyxin B1-1 concentrations in human plasma and treated urine for the determination of bioequivalence and toxicokinetic parameters in clinical studies.

Background:Polymyxin B is an old antibiotic with increasing clinical relevance in the treatment of multidrug-resistant Gram-negative bacterial infections. However, current dosing regimens are largely empiric as clinical pharmacological characterization of the drug has been hindered by the lack of assays to measure polymyxin B in human plasma.Methods:A high-performance liquid chromatography-mass spectrometry assay was developed to quantify polymyxin B1 and B2 in human plasma using pure calibrators. After purification with a solid-phase extraction column, polymyxin B1 and B2 were separated on a C18 column by gradient chromatography with an overall runtime of 12 minutes. Polymyxin B1 and B2 were ionized by positive electrospray ionization, and the resulting ions specific to polymyxin B1 and B2 were monitored (selected ion recording).Results:The dominant ions produced were (M + 2H) at m/z 602.6 and 595.5 for polymyxin B1 and polymyxin B2, respectively. The assay was linear between concentrations of 100 and 2500 ng/mL, with interday precision of 5.9% and 3.4% at 100 ng/mL and 5.3% and 4.0% at 2000 ng/mL for polymyxin B1 and polymyxin B2, respectively. Accuracy was 80.2% and 82.2% at 100 ng/mL and 99.9% and 109.6% at 2000 ng/mL for polymyxin B1 and polymyxin B2, respectively. No interference from other drugs commonly administered with polymyxin B was detected. The performance of the assay is affected by gross hemolysis and hyperlipemia. The method was successfully applied to patient samples. Interestingly, in a single patient the ratio of B1 and B2 did not change over a period of 12 hours after administration of the drug.Conclusions:A simple method for the simultaneous measurement of polymyxin B1 and polymyxin B2 in human plasma is described, which has the potential to optimize clinical use of this valuable antibiotic by permitting pharmacokinetic studies and therapeutic drug monitoring.

Introduction:The correlation between total and free polymyxin B (PMB including PMB1 and PMB2) exposure in vivo and acute kidney injury (AKI) remains obscure. This study explores the relationships between plasma exposure of PMB1 and PMB2 and nephrotoxicity, and investigates the risk factors for PMB-induced acute kidney injury (AKI) in critically ill patients.Methods:Critically ill patients who used PMB and met the criteria were enrolled. The total plasma concentration and plasma binding of PMB1 and PMB2 were analysed by liquid chromatography-tandem mass spectrometry and equilibrium dialysis.Results:A total of 89 patients were finally included, and AKI developed in 28.1% of them. The peak concentration of PMB1 (Cmax(B1)) (adjusted odds ratio (AOR) = 1.68, 95% CI 1.08-2.62, p = 0.023), baseline BUN level (AOR = 1.08, 95% CI 1.01-1.16, p = 0.039) and hypertension (AOR = 3.73, 95% CI 1.21-11.54, p = 0.022) were independent risk factors for PMB-induced AKI. The area under the ROC curve of the model was 0.799. When Cmax(B1) was 5.23 μg/ml or more, the probability of AKI was higher than 50%. The ratio of PMB1/PMB2 decreased after PMB preparation entered into the body. The protein binding rate in critically ill patients indicated significant individual differences. Free Cmax(B) and free Cmax(B1) levels in the AKI group were significantly (p < 0.05) higher than those in the non-AKI group. Total and free concentrations of PMB in patients showed a positive correlation.Conclusions:Both the ROC curve and logistic regression model showed that Cmax(B1) was a good predictor for the probability of PMB-induced AKI. Early therapeutic drug monitoring (TDM) of PMB should be considered in critically ill patients. Compared with Cmin(B), Cmax(B) and Cmax(B1) may be helpful for the early prediction of PMB-induced AKI in critically ill patients.