OBJECTIVE To establish a method for simultaneous determination of ceftazidime， avibactam and aztreonam concentrations in human plasma.METHODS Stable-isotope-labeled compounds ceftazidime-D 5 ， avibactam- 13 C 5 and aztreonam- 2 H 6 were used as internal standards. Plasma samples were pretreated by protein precipitation with methanol， followed by nitrogen blowing. A ultra-performance liquid chromatography-tandem mass spectrometry （UPLC-MS/MS） technique was applied to develop a quantitative analytical method for simultaneous measurement of ceftazidime， avibactam and aztreonam in human plasma. An ACQUITY UPLC BEH C 18 column was used as the chromatographic column. Gradient elution was performed with 0.01% formic acid-acetonitrile solution as the mobile phase at a flow rate of 0.3 mL/min. The column temperature was set at 40 ℃， and the injection volume was 5 μL. An electrospray ionization source was operated in both positive and negative ion modes for multiple reaction monitoring. Method validation was carried out according to the Guidelines for Bioanalytical Method Validation contained in volume Ⅳ of the 2020 edition of Chinese Pharmacopoeia .RESULTS The linear ranges of ceftazidime， avibactam and aztreonam were 0.04-200， 0.05-50，0.01-50 μg/mL， respectively， with all correlation coefficients no less than 0.996. The relative error （RE） for accuracy was no more than 12.25% （ n ＝5）， and the RSD for precision was no more than 13.49% （ n ＝5）. The RSD of internal-standard-normalized matrix factors was less than 15.00% （ n ＝6）. The RE in stability tests was lower than 15.00% （ n ＝3）.CONCLUSIONS This study successfully established an UPLC-MS/MS method for simultaneous determination of ceftazidime， avibactam and aztreonam concentrations in human plasma. The method possesses favorable accuracy， precision and stability， and can provide methodological support for therapeutic drug monitoring and individualized medication in patients treated with these three combined drugs.

OBJECTIVE To establish a UPLC-MS/MS method for the determination of plasma concentration of three carbapenem antibiotics， i.e. ertapenem （ETP）， imipenem （IPM） and meropenem （MEM）. METHODS After protein precipitation with methanol， the plasma samples were separated by ACQUITY UPLC BEH C18 column （2.1 mm×50 mm， 1.7 μm） using stable isotopes of three antibiotics （ETP-D4， IPM-D4， MEM-D6） as the internal standard. The mobile phases were 98% acetonitrile +2% water +0.1% formic acid and 98% water +2% acetonitrile +0.1% formic acid， by gradient elution. The flow rate was 0.3 mL/min and the column temperature was 40 ℃. Scanning analysis was performed in the positive ion and multiple reaction monitoring mode. RESULTS The method had good specificity， good linearity （r2≥0.993） in the range of 0.2-200， 0.1-100 and 0.1-100 μg/mL of ETP， IPM and MEM， and good intra-batch and inter-batch precision and accuracy （all RE≤5.14%， all RSD≤11.15%）， the matrix effect and extraction recovery were consistent （RSD≤12.99%）. CONCLUSIONS This study establishes the UPLC-MS/MS method to simultaneously quantify the plasma concentration of ETP， IPM and MEM. The method has the advantages of simple pretreatment， short detection time and small sample quantity to meet clinical requirement.

Objective To investigate the pollution of antibiotic resistance genes (ARGs) in the Lhasa River and provide a scientific basis for the safety of drinking water for the regional population and the prevention and control of water environment pollution. Methods A total of five water samples were collected in the Lhasa River in July 2022. Using quantitative real-time polymerase chain reaction (qPCR) assay, 19 types of ARGs, including eight ^“last-resort^” ARGs (LARGs) were detected and analyzed. Statistical analysis was conducted using the SPSS 22.0 software, and Student's t-test was used to compare data between two groups. Results All the 19 ARGs were detected with high frequencies, with the aminoglycoside resistance gene aadA having the highest concentration, followed by the sulfonamide resistance gene sul1 and the macrolide resistance gene ermB. Among the eight LARGs, the carbapenem resistance gene blaOXA-48 had the highest concentration. The absolute and relative concentrations of LARGs were lower than those of common ARGs. There was a statistically significant difference in the absolute concentrations between them, but no significant difference was observed in the relative concentrations. Conclusion Both ^“conventional^” ARGs and LAGRs have been detected in the Lhasa River. Although they are at a relatively low level compared to other domestic waters, in view of the serious adverse effects that ARGs, especially LARGs, may cause, the pollution of ARGs in the Lhasa River should be taken seriously.