Pharmacokinetics and metabolism of ulixertinib in rat by liquid chromatography combined with electrospray ionization tandem mass spectrometry.

The purpose of this study was to develop and validate a simple and sensitive liquid chromatography tandem mass spectrometry method for the determination of ulixertinib in rat plasma. The plasma samples were precipitated with acetonitrile and then separated on a C18 column with water containing 0.1% formic acid and acetonitrile as mobile phase at a flow rate of 0.3 mL/min. Analytes were monitored on a TSQ Vantage triple quadrupole tandem mass spectrometer operated in positive electrospray ionization mode. Selected reaction monitoring transitions were m/z 433.1→262.1 for ulixertinib and m/z 450.1→260.1 for internal standard. The assay achieved good linearity over the concentration range of 0.1-1000 ng/mL with correlation coefficient > 0.9991. The validated assay has been successfully applied to pharmacokinetic study of ulixertinib in rat after oral and intravenous administration. The results revealed that ulixertinib showed high exposure in rat plasma, low clearance, moderate oral bioavailability (45.13%), and dose-independent pharmacokinetic profiles over the oral dose range of 1-15 mg/kg. In addition, six metabolites from rat plasma and hepatocytes were detected and structurally identified by ultra-high performance liquid chromatography combined with high-resolution mass spectrometry. The metabolic pathways of ulixertinib referred to hydroxylation and dealkylation and glucuronidation.

Distribution of the multidrug efflux pump genes, adeABC, adeDE and adeIJK, and class 1 integron genes in multiple-antimicrobial-resistant clinical isolates of Acinetobacter baumannii-Acinetobacter calcoaceticus complex.

Of 112 non-repetitive clinical isolates of Acinetobacter baumannii-Acinetobacter calcoaceticus complex, 80% were resistant to a variety of structurally unrelated antimicrobials although all isolates were susceptible to minocycline and polymyxin. Resistance to carbapenems occurred in 8% of the isolates. The presence of adeSR-adeABC, adeDE and adeIJK drug efflux system genes and class 1 integron genes (integrase gene int1) was assessed by polymerase chain reaction (PCR) in relation to the susceptibility of the isolates to 20 antimicrobials. The majority of isolates (75%) with high levels of multidrug resistance were positive for adeSR-adeABC and adeIJK as well as int1 and thus belong to A. baumannii (i.e. genomospecies 2). Positive adeE was only observed in adeSR-adeABC/adeIJK/int1-negative isolates (8%; likely belonging to Acinetobacter genomospecies 3) that were relatively susceptible to several agents, and adeE expression was undetectable. The results reveal a possible association between adeABC/adeIJK and int1 in multidrug-resistant isolates of A. baumannii. In addition, differential distribution of the resistance-nodulation-cell division (RND) genes can likely be used as indicators for differentiating Acinetobacter species.

Molecular characterization of extended-spectrum beta-lactamases produced by clinical isolates of Enterobacter cloacae from a Teaching Hospital in China.

Of 59 clinical isolates of Enterobacter cloacae from a teaching hospital in Sichuan, China, 18 isolates were shown to be resistant to oxyimino cephalosporins and aztreonam. Enterobacterial repetitive consensus PCR revealed that these isolates comprised 7 distinct genotypes. The presence of plasmids in the 18 clinical isolates was revealed by conjugational transfer of plasmids from E. cloacae to Escherichia coli with the further isolation of the plasmids in the transconjugants. Subsequent nucleotide sequencing and beta-lactamase isoelectric focusing indicated that the plasmids encoded blaSHV, blaCTX-M and/or blaTEM genes, including genes for CTX-M-22 (13 strains), TEM-1 (12 strains), TEM-29 (1 strain), TEM-141 (1 strain), TEM-157 (1 strain), SHV-5 (1 strain), SHV-12 (1 strain), and SHV-70 (1 strain). The widespread presence of extended-spectrum beta-lactamases in E. cloacae isolated from the southwest of China was likely due to the dissemination of resistance plasmids with the predominant genotype of blaCTX-M-22.

Characterization of CTX-M-22 and TEM-141 Encoded by a single plasmid from a clinical isolate of Enterobacter cloacae in China.

We analyzed the resistance to expanded-spectrum cephalosporins of an Enterobacter cloacae clinical isolate, EC002, by transconjugation, isoelectric-focusing analysis, and cloning experiments. It produced two beta-lactamases with isoelectric point values of 5.4 and 8.7, corresponding to TEM-141, a novel variant of TEM-1, and CTX-M-22, encoded by a transferable plasmid.