Pharmacokinetics and pharmacodynamics of multiple-dose intravenous nemonoxacin in healthy Chinese volunteers.

This study evaluated the safety and pharmacokinetic/pharmacodynamic profiles of nemonoxacin in healthy Chinese volunteers following multiple-dose intravenous infusion once daily for 10 consecutive days. The study was composed of two stages. In the open-label stage, 500 mg or 750 mg of nemonoxacin (n = 12 each) was administered at an infusion rate of 5.56 mg/min. In the second stage, with a randomized double-blind placebo-controlled design, 500, 650, or 750 mg of nemonoxacin (n = 16 in each cohort; 12 subjects received the drug and the other 4 subjects received the placebo) was given at an infusion rate of 4.17 mg/min. The results showed that, in the first stage, the maximal nemonoxacin concentrations (mean ± SD) at steady state (Cmax_ss) were 9.60 ± 1.84 and 11.04 ± 2.18 µg/ml in the 500-mg and 750-mg cohorts, respectively; the areas under the concentration-time curve at steady state (AUC0-24_ss) were 44.03 ± 8.62 and 65.82 ± 10.78 µg · h/ml in the 500-mg and 750-mg cohorts, respectively. In the second stage, the nemonoxacin Cmax_ss values were 7.13 ± 1.47, 8.17 ± 1.76, and 9.96 ± 2.23 µg/ml in the 500-mg, 650-mg, and 750-mg cohorts, respectively; the AUC0-24_ss values were 40.46 ± 9.52, 54.17 ± 12.10, and 71.34 ± 17.79 µg · h/ml in the 500-mg, 650-mg, and 750-mg cohorts, respectively. No accumulation was found after the 10-day infusion with any regimen. The drug was well tolerated. A Monte Carlo simulation indicated that the cumulative fraction of response of any dosing regimen was nearly 100% against Streptococcus pneumoniae. The probability of target attainment of nemonoxacin therapy was >98% when the MIC of nemonoxacin against S. pneumoniae was ≤1 mg/liter. It is suggested that all of the studied intravenous nemonoxacin dosing regimens should have favorable clinical and microbiological efficacies in future clinical studies. (This study has been registered at ClinicalTrials.gov under registration no. NCT01944774.).

Pharmacokinetics and pharmacodynamics of nemonoxacin against Streptococcus pneumoniae in an in vitro infection model.

The aim of this paper was to investigate the pharmacokinetics (PK) and pharmacodynamics (PD) of nemonoxacin, a novel nonfluorinated quinolone, against Streptococcus pneumoniae in vitro. A modified infection model was used to simulate the pharmacokinetics of nemonoxacin following scaling of single oral doses and multiple oral dosing. Four S. pneumoniae strains with different penicillin sensitivities were selected, and the drug efficacy was quantified by the change in log colony counts within 24 h. A sigmoid maximum-effect (Emax) model was used to analyze the relationship between PK/PD parameters and drug effect. Analysis indicated that the killing pattern of nemonoxacin shows a dualism which is mainly concentration dependent when the MIC is low and that the better PK/PD index should be the area under the concentration-time curve for the free, unbound fraction of the drug divided by the MIC (fAUC0-24/MIC), which means that giving the total daily amount of drug as one dose is appropriate under those conditions. When the MIC is high, the time (T) dependency is important and the valid PK/PD index should be the cumulative percentage of a 24-h period in which the drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (f%T>MIC), which means that to split the maximum daily dose into several separate doses will benefit the eradication of the bacteria. To obtain a 3-log10-unit decrease, the target values of fAUC0-24/MIC and f%T>MIC are 47.05 and 53.4%, respectively.

Activities of colistin- and minocycline-based combinations against extensive drug resistant Acinetobacter baumannii isolates from intensive care unit patients.

BACKGROUND: Extensive drug resistance of Acinetobacter baumannii is a serious problem in the clinical setting. It is therefore important to find active antibiotic combinations that could be effective in the treatment of infections caused by this problematic 'superbug'. In this study, we analyzed the in vitro activities of three colistin-based combinations and a minocycline-based combination against clinically isolated extensive drug resistant Acinetobacter baumannii (XDR-AB) strains. METHODS: Fourteen XDR-AB clinical isolates were collected. The clonotypes were determined by polymerase chain reaction-based fingerprinting. Susceptibility testing was carried out according to the standards of the Clinical and Laboratory Standards Institute. Activities of drug combinations were investigated against four selected strains and analyzed by mean survival time over 12 hours (MST12 h) in a time-kill study. RESULTS: The time-kill studies indicated that the minimum inhibitory concentration (MIC) of colistin (0.5 or 0.25 µg/mL) completely killed all strains at 2 to 4 hours, but 0.5×MIC colistin showed no bactericidal activity. Meropenem (8 µg/mL), minocycline (1 µg/mL) or rifampicin (0.06 µg/mL) did not show bactericidal activity. However, combinations of colistin at 0.5×MIC (0.25 or 0.125 µg/mL) with each of the above were synergistic and shown bactericidal activities against all test isolates. A combination of meropenem (16 µg/mL) with minocycline (0.5×MIC, 4 or 2 µg/mL) was synergitic to all test isolates, but neither showed bactericidal activity alone. The MST12 h values of drug combinations (either colistin- or minocycline-based combinations) were significantly shorter than those of the single drugs (p<0.01). CONCLUSIONS: This study indicates that combinations of colistin/meropenem, colistin/rifampicin, colistin/minocycline and minocycline/meropenem are synergistic in vitro against XDR-AB strains.

Coexistence of qnrB4 and qnrS1 in a clinical strain of Klebsiella pneumoniae.

AIM: To identify the location and the relationship, and to analyze the genetic background of 2 plasmid-mediated quinolone resistance genes, qnrB4 and qnrS1, carried by a clinical strain of Klebsiella pneumoniae (K pneumoniae). METHODS: The plasmids carrying qnrB4 or qnrS1 were identified by Southern blotting. A HindIII fragment containing qnrB4 or qnrS1 was cloned into plasmid puc18 and sequenced. RESULTS: qnrB4 and qnrS1 were located on 2 different plasmids, pHS7 and pHS8, and were 180 and 45 kb in size, respectively. A transconjugant carrying plasmid pHS7 bearing qnrB4 and another transconjugant carrying pHS9 bearing qnrB4 and qnrS1 were obtained by conjugation. Plasmid pHS8 bearing qnrS1 was also transferred to J53 by transformation. The ciprofloxacin minimal inhibitory concentrations (MIC) for J53 transconjugants or the transformant carrying qnrB4 only, qnrS1 only, and both qnrB4 and qnrS1 were 0.19, 0.25, and 0.25 mg/L, respectively, while the parent clinical strain of K pneumoniae had a MIC of 0.75 mg/L. qnrB4 was located in a sul1-type integron with blaDHA-1, ampR and psp genes in upstream and insertion sequence IS26, and sap genes in downstream of qnrB4. qnrS1 was not located in an integron, but IS26 was found both upstream and downstream, and IS2 was found directly upstream of qnrS1. CONCLUSION: qnrB and qnrS can be harbored simultaneously by a single clinical strain of K pneumoniae. These 2 genes are carried by 2 different plasmids and have different genetic environments in plasmid DNA structure.

[Mechanisms of pandrug-resistance of Pseudomonas aeruginosa].

OBJECTIVE: To explore the mechanisms of pandrug-resistance (PDR) of Pseudomonas aeruginosa (PA). METHODS: Nineteen strains of PA were collected from Huashan Hospital, Shanghai. Agar dilution method was used to detect the levels of minimum inhibitory concentration (MIC) of 14 antimicrobial drugs to the PA strains. Strain homology was investigated by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR). To analyze the beta-lactam resistant mechanisms, genes of extended-spectrum beta-lactamases (ESBLs), carbapenemase, and plasmid-mediated AmpC were amplified and analyzed by PCR and DNA sequencing. To analyze the aminoglycoside resistant mechanisms, 16 aminoglycoside modifying enzyme were screened by PCR. PCR and DNA sequencing were used to amplify and analyze the genes of DNA gyrase genes gyrA and gyrB, topoisomerase IV genes parC and pare, and qnr gene for the fluoroquinolone resistance mechanisms, to amplify and analyze study the oprD2 coding genes and inhibitor MC207110 were used to detect efflux pump for the carbapenem resistance mechanisms. RESULTS: Five types were identified in the 19 PDR-PA by ERIC-PCR, mainly type A (n=6) and type B (n=7). 17 of the 19 PDR-PA strains produced VEB-3 type ESBL, 1 strain of which also produced OXA-10 type ESBL simultaneously. Both of the carbapenemase and plasmid-mediated AmpC were negative. All of the 19 PDR-PA strains produced aminoglycoside modifying enzyme, yielding ant (3") I and 18 strains of which produced aac (3) II simultaneously. All 19 PDR-PA strains carried gyrA mutations, 14 of which carried parC mutation simultaneously, qnr gene was negative. OprD2 coding gene sequencing analysis revealed that small fragment missing occurred to all oprD2 genes of the 19 strains. 16 strains showed efflux pump mechanism. CONCLUSION: The resistance mechanism of PDR-PA to cephalosporins, beta-lactam/beta-lactamase inhibitor, carbapenem, fluoroquinolones, and aminoglycosides are due to production of VEB-3-ESBL, aac (3) II, and ant (3") I aminoglycoside modifying enzyme, mutations of DNA gyrase gyrA and topoisomerase parC gene, OprD2 protein deficiencies, and efflux pump overexpression.

[Changes of antimicrobial resistance among clinical isolates of Escherichia coil in Shanghai 1990-2004].

OBJECTIVE: To investigate the trend of resistance to antimicrobial agents among clinical isolates of Escherichia coli 1990-2004. METHODS: Agar diffusion test was used to analyze the changes of drug susceptibility of 33,495 strains of E. coli isolated from 11 hospitals in Shanghai to 21 antimicrobial agents 1990-2004. RESULTS: The resistance rates of 33,495 E.coli isolates to 21 antimicrobial agents mostly increased 1990-2004. The resistance rates to ampicillin and piperacillin increased from 69% and 30% to 85% and 71.4% respectively. The resistance rates to cephalosporins, except ceftazidime and cefepime, all increased, e. g., the resistance rates to cefazolin (24.0%-->48.3%), cefuroxime (18.0%-->45.7%), and cefaclor (33.3%-->46.8%), especially that to cefotaxime (6.0%-->35.2%). The resistance rate to fluoroquinolones increased from 11.0% to 55.4%. The resistance rate to gentamicin increased from 44.0% to 54.0%. The resistance rates to tetracycline, chloramphenicol, SMZ/TMP remained at high levels. However, ceftazidime, cefepime, imipenem, amikacin, beta-lactams/beta-lactamase inhibitors, and nitrofurantoin remained active against the E.coli isolates. The detectable rate of extended-spectrum beta-lactamase-producing strains in E. coli increased from 14.7% to 36.5%. CONCLUSION: The trend of resistance of E. coli to commonly used antimicrobials was upward 1990-2004.

[Study of pharmacokinetics/pharmacodynamics of levofloxacin].

OBJECTIVE: To evaluate the dosing regimens of levofloxacin. METHODS: The drug concentrations in serum and urine were assayed by HPLC method and the pharmacokinetic parameters were calculated after intravenous infusion of a single dose of 200 mg, 300 mg and 500 mg levofloxacin to healthy volunteers. The in vitro activity MIC of levofloxacin against 823 clinical isolates were determined and compared with other antimicrobial agents. Based on the above results, the PK/PD parameters C(max)/MIC and AUC/MIC were calculated and the dosing regimens of levofloxacin were proposed for infections caused by different pathogens. RESULTS: The results of clinical pharmacokinetic study showed that the C(max) of levofloxacin was 3.4 mg/L +/- 0.8 mg/L, 4.8 mg/L +/- 1.4 mg/L and 7.6 mg/L +/- 1.1 mg/L respectively, AUC(0-infinity) was 14.4 mg.h/L +/- 2.5 mg.h/L, 21.9 mg.h/L +/- 4.5 mg.h/L and 38.3 mg.h/L +/- 4.9 mg.h/L respectively, T(1)/2 beta was 6.2 h +/- 0.4 h, 6.4 h +/- 0.9 h and 6.5 h +/- 0.6 h respectively, and 69% +/- 5%, 69% +/- 6%, and 65% +/- 4% of the doses were excreted in urine within 24 h after intravenous infusion of a single dose of levofloxacin 200 mg, 300 mg and 500 mg. The in vitro pharmacodynamic study showed that levofloxacin was highly active against Hemolytic streptococcus and Moraxella catarrhalis. It was active against Streptococcus pneumoniae (including penicillin nonsusceptible strains), Hemophilus influenzae, methicillin-sensitive Staphylococcus aureus (MSSA), Klebsiella pneumoniae and Stenotrophomonas maltophilia. Levofloxacin also had good activity against Pseudomonas aeruginosa and K.pneumoniae. However, most of isolates of enterococcal spp. were resistant to levofloxacin. Above 50% of Escherichia coli isolates were resistant to levofloxacin. Based on the results of PK/PD parameters, the adequate dosing regimens of levofloxacin should be once daily 200 mg once daily of levofloxacin was expected to be effective for the treatment of infections caused by M. catarrhalis. The regimen of 300 mg once daily could be effective for the treatment of infections caused by Hemolytic streptococcus. 500 mg once daily of levofloxacin was expected to be effective for the treatment of respiratory tract infections caused by S. pneumoniae or H. influenzae. For treatment of respiratory tract infections and urinary tract infections caused by levofloxacin-susceptible organisms including K. pneumoniae, E. coli, P. aeruginosa, and S.maltophilia, 500 mg once daily of levofloxacin was needed to obtain good clinical efficacy. But PK/PD parameters predicted that 500 mg daily of levofloxacin was not effective for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and Enterococci. CONCLUSION: The proposed dosing regimens of levofloxacin based on PK/PD concepts are expected to provide good efficacy in clinical practice.

In vitro activities of tigecycline against clinical isolates from Shanghai, China.

To evaluate the in vitro activity of tigecycline, the minimum inhibitory concentrations (MICs) of tigecycline against 1,201 strains of recent clinical isolates from 10 hospitals in Shanghai, China were determined and compared with selected comparators. Results showed that tigecycline had broad-spectrum antimicrobial activity. It was highly active against Gram-positive cocci, including methicillin-resistant Staphylococcus spp., penicillin-intermediate Streptococcus pneumoniae, Enterococcus faecalis and E. faecium. Tigecycline also had good activity against most strains of Enterobacteriaceae, Haemophilus influenzae, Neisseria gonorrhoeae, and Moraxella catarrhalis. However, it was poorly active against Acinetobacter baumannii and Pseudomonas aeruginosa. Tigecycline was highly active against anaerobic Gram-positive cocci such as Peptococcus spp. The in vitro activity of tigecycline was significantly better than that of minocycline and tetracycline. It was as active as or slightly more active than vancomycin and teicoplanin in the activity against resistant aerobic Gram-positive cocci. Tigecycline was bactericidal against all Gram-positive cocci tested except Enterococcus spp. Inoculum size but not pH of medium or concentration of human serum in broth had significant effect on the in vitro activity of tigecycline. Aged media (48-72 hours after preparation) used in the test and specific resistance problem in China may have some effects on MIC values of tigecycline.

[Identification and expression of blaCTX-M-14 and blaCTX-M-24].

OBJECTIVE: To identify the ESBL gene and the prevalence in Escherichia coli and Klebsiella pneumoniae strain isolated from Huashan Hospital, Shanghai. METHODS: Isolates were confirmed as an ESBL producing strain by double-disk synergy test and NCCLS Confirmatory Test. Antibiotic susceptibilities were determined by standard agar dilution procedure on Mueller-Hinton agar. To determine whether the resistance was transferable, the conjugation experiment was performed; plasmids were isolated from clinical isolates and transcojugants. The partial bla(gene) of ESBL producing isolates and their transcojugants were detected by PCR using universal primers for TEM, SHV, CTX-M-1group, Toho-1group, CTX-M-13group respectively. The entire bla(CTX-M-13) group were amplified by PCR using the primers outside the Open Reading Frame (ORF) of CTX-M-13group beta-lactamases; the PCR products of entire bla(CTX-M-13)group were cloned into vector and the recombinant plasmids were transformed into the recipient strain for expression; the PCR products were also directly sequenced and analyzed; the clinical isolates of ESBL producers were detected by PFGE. RESULTS: ESBL producers were resistant to most beta-lactams and non-beta-lactams. Most transconjugants were obtained at frequency of 10(-4) approximately 10(-5) and resistance to non-beta-lactams was cotransferred with the ESBL activity to the transconjugant. A plasmid of about > 23.1 kb was obtained from each tansconjugant by plasmid extraction. Partial gene amplification products of CTX-M-13 group gene were obtained from isolates and their transconjugants. The bla(CTX-M-13)group from 4 transconjugants were identified as bla(CTX-M-14), and other six were bla(CTX-M-24); those ESBLs were mediated by plasmids (> 23.1 kb); the transformants producing CTX-M-14 or CTX-M-24 were resistant to most beta-lactams, which were much more resistant to cefotaxime than to ceftazidine; PFGE patterns of those isolates were different. CONCLUSION: clinical isolate of Escherichia coli and Klebsiella pneumoniae isolated from Huashan Hospital, Shanhai produced CTX-M-14 or CTX-M-24, which caused the isolate resistant to most beta-lactams; no clone spread in those isolates was found.

Prevalence of clinical meticillin-resistant Staphylococcus aureus (MRSA) with high-level mupirocin resistance in Shanghai and Wenzhou, China.

A total of 803 clinical meticillin-resistant Staphylococcus aureus (MRSA) isolates obtained from Shanghai and Wenzhou in China were subjected to a screening test by disk diffusion for detection of mupirocin resistance. Among the 803 strains, 53 (6.6%) were mupirocin-resistant. Of these 53 strains, all were discovered by the agar dilution method and polymerase chain reaction (PCR) to be high-level mupirocin-resistant and to harbour the mupA gene. Plasmid DNA hybridisation and curing experiments disclosed that mupA was located on a large plasmid varying in size between 23.0kb and 52.4kb in all strains. Susceptibility testing of 10 antibiotics revealed that resistance rates between the Shanghai isolates and the Wenzhou isolates to trimethoprim/sulfamethoxazole and rifampicin differed significantly. Molecular typing by pulsed-field gel electrophoresis (PFGE), staphylococcal chromosomal cassette mec (SCCmec) and staphylococcal protein A (spa) revealed that PFGE A-SCCmec IIIA-spa t030 and PFGE B-SCCmec IIIA-spa t030 represented all of the Wenzhou strains, whereas PFGE N-SCCmec I-spa t318, PFGE P-SCCmec III-spa t037, PFGE I-SCCmec III-spa t037 and PFGE M-SCCmec IIIA-spa t002 were the predominant profiles among Shanghai isolates. These findings indicated that high-level mupirocin resistance mediated by plasmids prevailed in the clinical mupirocin-resistant MRSA from Shanghai and Wenzhou and was mainly related to the transmission of clones.