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OBJECTIVES A rapid, sensitive and robust ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the quantification of four major polymyxin B components (polymyxin B1, polymyxin B2, polymyxin B3 and isoleucine-polymyxin B1) in serum and epithelial lining fluid (ELF) samples. METHODS A Waters Acquity UPLC HSS C18 column was used with 0.1% formic acid in water/acetonitrile as mobile phases. Analysis was performed in a positive ionization mode with multiple-reactions monitoring scan type. Five percent trichloroacetic acid was used to precipitate proteins in biological samples and to increase the sensitivity of detection. RESULTS Our results showed a linear concentration range of 0.0065-3.2 mg/L for all the major polymyxin B components in both serum and ELF, respectively; the interday variation was

Purpose The stability of polymyxin B sulfate in infusion bags containing 0.9% sodium chloride injection stored at 4 and 25 °C was studied. Methods Seven manufacturing batches of polymyxin B from different sources were tested. The products were reconstituted in sterile water for injection, diluted in infusion bags containing 0.9% sodium chloride injection, and stored at room temperature (25 °C) or under refrigeration (4 °C). Samples were withdrawn at the same time on days 0, 1, 2, 3, 5, and 7. A modified microbiological assay was used to determine the concentrations, as indicated by zones of inhibition, of polymyxin B. Bordetella bronchiseptica served as the reference organism. Stability was defined as retention of >90% of the initial concentration. The decomposition kinetics of polymyxin B in 0.9% sodium chloride injection were evaluated by plotting the polymyxin B concentration remaining versus time. Results On average, the samples retained over 90% of their initial concentration for up to two days at both storage temperatures. All samples retained over 90% of their initial concentration at 24 hours. The decomposition kinetics of polymyxin B in infusion bags containing 0.9% sodium chloride injection exhibited pseudo-first-order kinetics, with rate constants of 0.024–0.075 day−1 at 25 °C and 0.022–0.043 day−1 at 4 °C ( p > 0.05). Conclusion Polymyxin B was stable for at least one day when stored at 4 or 25 °C in infusion bags containing 0.9% sodium chloride injection. Stability did not differ significantly between the two storage temperatures.