Nan Bai

Colistin resistance of Acinetobacter baumannii: clinical reports, mechanisms and antimicrobial strategies

Colistin is the last resort for treatment of multidrug-resistant Acinetobacter baumannii. Unfortunately, resistance to colistin has been reported all over the world. The highest resistance rate was reported in Asia, followed by Europe. The heteroresistance rate of A. baumannii to colistin is generally higher than the resistance rate. The mechanism of resistance might be loss of lipopolysaccharide or/and the PmrAB two-component system. Pharmacokinetic/pharmacodynamic studies revealed that colistin monotherapy is unable to prevent resistance, and combination therapy might be the best antimicrobial strategy against colistin-resistant A. baumannii. Colistin/rifampicin and colistin/carbapenem are the most studied combinations that showed promising results in vitro, in vivo and in the clinic. New peptides showing good activity against colistin-resistant A. baumannii are also being investigated.

Systematic Review and Meta-Analysis of the Effectiveness and Safety of Tigecycline for Treatment of Infectious Disease

ABSTRACT The aim of this study was to compare the efficacy and safety of tigecycline, a newly developed glycylcycline antibiotic, with those of empirical antibiotic regimens which have been reported to possess good efficacy for complicated skin and skin structure infections (cSSSIs), complicated intra-abdominal infections (cIAIs), community-acquired pneumonia (CAP), and other infections caused by methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant Enterococcus (VRE). A meta-analysis of randomized controlled trials (RCTs) identified in PubMed, the Cochrane Library, and Embase was performed. Eight RCTs involving 4,651 patients were included in the meta-analysis. Compared with therapy with empirical antibiotic regimens, tigecycline monotherapy was associated with similar clinical treatment success rates (for the clinically evaluable [CE] population, odds ratio [OR] = 0.92, 95% confidence interval [CI] = 0.76 to 1.12, P = 0.42; for the clinical modified intent-to-treat [c-mITT] population, OR = 0.86, 95% CI = 0.74 to 1.01, P = 0.06) and similar microbiological treatment success rates (for the microbiologically evaluable [ME] population, OR = 0.86, 95% CI = 0.69 to 1.07, P = 0.19). The incidence of adverse events in the tigecycline group was significantly higher than that in the other therapy groups with a statistical margin (for the modified intent-to-treat [mITT] population, OR = 1.33, 95% CI = 1.17 to 1.52, P < 0.0001), especially in the digestive system (mITT population, OR = 2.41, 95% CI = 1.67 to 3.46, P < 0.00001). No difference regarding all-cause mortality and drug-related mortality between tigecycline and the other regimens was found, although numerically higher mortality was found in the tigecycline group. This meta-analysis provides evidence that tigecycline monotherapy may be used as effectively as the comparison therapy for cSSSI, cIAIs, CAP, and infections caused by MRSA/VRE. However, because of the high risk of mortality, AEs, and emergence of resistant isolates, prudence with the clinical use of tigecycline monotherapy in infections is required.

The emergence of clinical resistance to tigecycline.

Tigecycline (TIG) exhibits broad-spectrum activity against many Gram-positive and Gram-negative pathogens. However, clinical resistance has emerged recently and has been detected following treatment with TIG. This observation suggests that long-term monotherapy may carry a high risk for TIG resistance. TIG resistance is observed most frequently in Acinetobacter baumannii and Enterobacteriaceae, especially in multidrug-resistant strains. Resistance-nodulation-cell division (RND)-type transporters and other efflux pumps may be factors for decreased sensitivity to TIG. Therefore, TIG should be cautiously used in the clinic, and efflux-mediated resistance should be closely monitored in order to prolong the lifespan of this useful antibiotic.

Effectiveness and safety of macrolides in cystic fibrosis patients: a meta-analysis and systematic review

OBJECTIVES To evaluate the efficacy and safety of macrolides in cystic fibrosis (CF). METHODS Randomized controlled trials (RCTs) of macrolides for the treatment of CF published in PubMed, the Cochrane Library and Embase were searched. Application of inclusion and exclusion criteria, data extraction, and assessment of methodological quality were independently performed in duplicate. The primary efficacy outcome was the impact on the deterioration of lung function (changes in FEV(1) and FVC). Safety outcomes included adverse events and mortality. RESULTS Eight RCTs (seven with azithromycin and one with clarithromycin) were found in the systematic review and six RCTs with azithromycin (654 patients) were included in the meta-analysis. Azithromycin treatment showed a significant increase in FEV(1)% (3.22%, 95% CI = 1.38-5.06, P = 0.0006, I(2) = 0%) and FVC% (3.23%, 95% CI = 1.62-4.85, P < 0.0001, I(2) = 0%) compared with placebo. In individuals with baseline Pseudomonas aeruginosa colonization, both FEV(1)% (4.80%, 95% CI = 1.66-7.94, P = 0.003, I(2) = 42%) and FVC% (4.74%, 95% CI = 1.92-7.57, P = 0.001, I(2) = 0%) increased significantly. The incidence rates of the main side effects (cough, headache, abdominal pain, vomiting, nausea and diarrhoea) were not significantly different between the azithromycin-treated group and the placebo group. The RCT of clarithromycin, involving 18 patients, showed its effects on clinical improvement; however, the small sample size made comparisons with azithromycin difficult. CONCLUSIONS Long-term use of azithromycin can improve lung function, especially for P. aeruginosa-colonized CF patients. There was no evidence of increased adverse events with azithromycin. More data are needed to verify the best azithromycin regimen and to evaluate other macrolides in CF patients.

Mutant Prevention Concentration-Based Pharmacokinetic/Pharmacodynamic Indices as Dosing Targets for Suppressing the Enrichment of Levofloxacin-Resistant Subpopulations of Staphylococcus aureus

ABSTRACT MIC- and mutant prevention concentration (MPC)-based pharmacokinetic/pharmacodynamic (PK/PD) indices were compared for suitability as attainment targets for restricting amplification of levofloxacin-resistant mutant subpopulations. When three Staphylococcus aureus strains were examined with a hollow-fiber PK/PD model, area under the concentration-time curve over 24 h (AUC24)/MPC values of >25 and maximum concentration of drug in serum (Cmax)/MPC values of >2.2 predicted resistance outcome among different isolates with an interisolate kappa coefficient of 1. MIC-based mutant-restrictive PK/PD values varied >8-fold and exhibited only a moderate interisolate agreement (kappa coefficient of 0.5). Thus, MPC-based PK/PD indices are more suitable than MIC-based indices for predicting mutant-restricting fluoroquinolone doses when multiple bacterial isolates are considered.

In vitro antimicrobial activity and mutant prevention concentration of colistin against Acinetobacter baumannii.

ABSTRACT The antimicrobial activities of colistin and other antibiotics against clinical Acinetobacter baumannii and the mutant prevention concentration (MPC) of colistin against multidrug-resistant A. baumannii were studied. All 70 stains tested were sensitive to colistin. The MPC range of colistin against 30 multidrug-resistant A. baumannii stains was approximately 32 to >128 μg/ml, and the MPC at which 90% of the isolates tested were prevented (MPC90) exceeded 128 μg/ml, which was much higher than the plasma concentration of colistin at the current recommended dosage. So, combination therapy for colistin treatment of A. baumannii would be prudent to slow the emergence of resistance.

In vitro effects of tigecycline in combination with colistin (polymyxin E) and sulbactam against multidrug-resistant Acinetobacter baumannii

The lack of active antimicrobial agents against multidrug-resistant (MDR) Acinetobacter baumannii has posed great threat to the public health. Combination therapies with antibiotics owning different antimicrobial mechanisms have been proposed as good options for treating MDR A. baumannii infections. This study was aimed to investigate the in vitro effects of tigecycline in combination with colistin and sulbactam against MDR A. baumannii. A total of 70 strains from two hospitals in China were examined in the study. The checkerboard method was used for determining synergistic activity of different antibiotic combinations. Tigecycline/colistin combination displayed synergistic and partial synergistic activity in 24.3% of the isolates, whereas the tigecycline/sulbactam combination showed synergistic and partial synergistic activity in 64.3% of the isolates. Neither of the combinations showed antagonism in this study. In addition, for evaluating the ability of combinations on resistance prevention, mutant prevention concentrations (MPCs) of tigecycline, colistin, sulbactam alone and tigecycline in combination with colistin and sulbactam were studied against MDR A. baumannii. Compared with tigecycline used alone, combination therapies could achieve lower MPCs of tigecycline. However, when the MPCs of dual-drug therapy were in conjunction with clinical pharmacokinetic profiles, combinations may not strictly curb the occurrence of resistance at current dosage regimen. In summary, this study suggested that combination therapy was a good option for treating MDR A. baumannii infections. But the finding that combination with these drugs at current dosage regimen may not prevent emergence of resistance warranted further studies on dosage of combined antibiotics required for achieving resistance prevention.

A meta-analysis of metronidazole and vancomycin for the treatment of Clostridium difficile infection, stratified by disease severity

The aim of this meta-analysis was to compare the efficacy of metronidazole and vancomycin for the treatment of Clostridium difficile infection, especially to investigate which agent was superior for treating either mild or severe C. difficile infection. A meta-analysis of randomized controlled trials and cohort studies identified in Pubmed, Embase, and the Cochrane Library was conducted. Four randomized controlled trials and two cohort studies involving 1218 patients were included in this meta-analysis. Metronidazole was inferior to vancomycin for treating C. difficile infection in terms of both initial clinical cure rates (risk ratio, RR=0.91, 95% confidence interval, CI=0.84-0.98, p=0.02) and sustained cure rates (RR=0.88, 95% CI=0.82-0.96, p=0.003). For mild C. difficile infection, the efficacy of metronidazole and vancomycin resulted in similar clinical cure rates (RR=0.94, 95% CI=0.84-1.04, p=0.21) and sustained cure rates (RR=0.93, 95% CI=0.83-1.05, p=0.26). For severe C. difficile infection the efficacy of vancomycin was superior to metronidazole in terms of clinical cure rates (RR=0.81, 95% CI=0.69-0.95, p=0.009), whereas sustained cure rates were similar (RR=0.86, 95% CI=0.72-1.02, p=0.08). Regarding microbiological cure metronidazole therapy was as effective as vancomycin therapy (RR=0.88, 95% CI=0.64-1.21, p=0.43). Recurrence rates with metronidazole and vancomycin for both mild C. difficile infection (RR=0.95, 95% CI=0.56-1.60, p=0.85) and severe C. difficile infection (RR=1.27, 95% CI=0.85-1.91, p=0.25) were not different. Likewise, no difference in all-cause mortality was found as well (RR=0.87, 95% CI=0.56-1.35, p=0.53). In conclusion, vancomycin provides improved initial clinical and sustained cure rates in patients with C. difficile infection compared with metronidazole, especially in patients with severe C. difficile infection. In view of these data, vancomycin may be considered first line therapy for severe C. difficile infection.

Treatment of community-acquired pneumonia with moxifloxacin: a meta-analysis of randomized controlled trials

Abstract Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality throughout the world. To investigate whether moxifloxacin monotherapy is associated with better clinical outcomes than other antibiotics recommended for CAP among adults with mild-to-moderate or severe CAP, we performed a meta-analysis. MEDLINE, EMBASE, Web of Science, and the Cochrane Library were searched for randomized control trials (RCTs). The efficacy and safety of moxifloxacin were compared with other antimicrobial agents used to treat CAP. Fourteen RCTs, consisting of 6923 total patients, were included in the meta-analysis. No difference was found regarding the incidence of adverse events and mortality between moxifloxacin and the compared regimens. We found that moxifloxacin is as effective and well-tolerated as other recommended antibiotics for the treatment of CAP and possesses a better pathogen eradication rate than beta-lactam-based therapy.

Weight-adjusted versus fixed dose of linezolid for Chinese healthy volunteers of higher and lower body weight: a Phase I pharmacokinetic and pharmacodynamic study

Objectives: The objective was to evaluate the pharmacokinetic and pharmacodynamic properties of a single intravenous fixed dose compared with a weight-adjusted dose of linezolid. Methods: A Phase I, comparative clinical trial was conducted involving 20 healthy male Chinese volunteers, assigned into low weight (LW) (50 kg < weight ≤ 55 kg) and high weight (HW) (≥ 80 kg) groups. All subjects were administrated single dose of linezolid (600 mg/30 min) and, after 72 h washout period, another single-dose (10 mg/kg/30 min). Plasma linezolid concentrations were measured by liquid chromatography-tandem mass spectrometry. A Monte Carlo simulation was used to evaluate the probability of pharmacodynamic target attainment (PTA). Results: With 600 mg dose, plasma concentrations in LW group were much higher than that in HW group. A persistent serum inhibitory activity was observed in LW group; the inhibitory activity was lower in HW group. The PTA in HW group was lower than in LW group. For 10 mg/kg dose, both HW and LW groups had similar plasma concentrations. The HW and LW groups had similar serum inhibitory effects. The PTA in HW and LW groups also showed no difference. Conclusions: Our findings suggest that a weight-adjusted, 10 mg/kg regimen of linezolid may be more appropriate than fixed dosing for patients of different body weight.