Determination of the pharmacodynamic activity of clinically achievable tigecycline serum concentrations against clinical isolates of Escherichia coli with extended-spectrum beta-lactamases, AmpC beta-lactamases and reduced susceptibility to carbapenems using an in vitro model

In vitro pharmacodynamics of omadacycline against Escherichia coli and Acinetobacter baumannii

BACKGROUND

The pharmacodynamics of omadacycline have been extensively studied against Gram-positive pathogens but less information is available for Gram-negative pathogens. We describe the pre-clinical pharmacodynamics of omadacycline against Escherichia coli and Acinetobacter baumannii.

METHODS

An in vitro dilutional pharmacokinetic model was used. Exposure experiments with fAUC/MIC ratios ranging from 0 to 1200 were performed using five strains of E. coli and five strains of A. baumannii. Reduction in bacterial load and changes in population profiles were measured.

RESULTS

The fAUC/MIC targets against E. coli for 24 h static and -1 log reduction in load were 25.3 ± 17.2 and 42.7 ± 32.5, respectively. For A. baumannii the fAUC/MIC for 24 h static effect was 108.1 ± 38.6. Changes in population profiles were observed for E. coli at fAUC/MIC ratios of ≤200 and for A. baumannii up to 1200. MICs were increased 2-32 fold.

CONCLUSIONS

fAUC/MIC targets for A. baumannii are greater than for E.coli and changes in population profiles more likely. E. coli fAUC/MIC targets align with in vivo data and will be useful in determining omadacycline dosing for this pathogen.

Colistin Increases the Cidal Activity of Antibiotic Combinations Against Multidrug-Resistant Klebsiella pneumoniae: An In Vitro Model Comparing Multiple Combination Bactericidal Testing at One Peak Serum Concentration and Time-Kill Method

The lack of treatment for multidrug-resistant (MDR) Enterobacteriaceae often leads to the use of double or triple antibiotic combinations to increase the option of clinical success. This study analyzes multiple combination bactericidal testing (MCBT) to screen double and triple antibiotic combinations, at standard peak serum concentration, for bactericidal activity against 21 MDR Klebsiella pneumoniae isolates. This method was compared with time-killing curves. The full bactericidal activity against all strains was obtained only by adding colistin. MCBT has a potential to become a rapid method for testing multiple antibiotic combinations for MDR microorganisms when colistin is used, providing clinicians with in vitro cidal data within 48 hr of strain isolation.

Clinical management of infections caused by multidrug-resistant Enterobacteriaceae

Enterobacteriaceae showing resistance to cephalosporins due to extended-spectrum β-lactamases (ESBLs) or plasmid-mediated AmpC enzymes, and those producing carbapenemases have spread worldwide during the last decades. Many of these isolates are also resistant to other first-line agents such as fluoroquinolones or aminoglycosides, leaving few available options for therapy. Thus, older drugs such as colistin and fosfomycin are being increasingly used. Infections caused by these bacteria are associated with increased morbidity and mortality compared with those caused by their susceptible counterparts. Most of the evidence supporting the present recommendations is from in vitro data, animal studies, and observational studies. While carbapenems are considered the drugs of choice for ESBL and AmpC producers, recent data suggest that certain alternatives may be suitable for some types of infections. Combined therapy seems superior to monotherapy in the treatment of invasive infections caused by carbapenemase-producing Enterobacteriaceae. Optimization of dosage according to pharmacokinetics/pharmacodynamics data is important for the treatment of infections caused by isolates with borderline minimum inhibitory concentration due to low-level resistance mechanisms. The increasing frequency and the rapid spread of multidrug resistance among the Enterobacteriaceae is a true and complex public health problem.

In vitro activity of carbapenems alone and in combination with amikacin against KPC-producing Klebsiella pneumoniae

Background

Although carbapenems are the primary treatment strategy for invasive infections caused by ESBL bacteria, case reports of these pathogens with reduced carbapenem susceptibility have emerged. One potential treatment modality is to optimize the use of anti-infectives with combination therapy. We evaluated the activity of carbapenems alone and in combination with amikacin against these clinical isolates.

Methods

Time-kill studies evaluated ertapenem (ETP), imipenem (IPM), meropenem (MEM), and amikacin (AMK) against 4 non-duplicate clinical isolates of Klebsiella pneumoniae that were resistant to these antibiotics. Synergy was defined as ≥ 2 log₁₀ decrease CFU/mL at 24 h for the combination when compared with the most active single agent of the combination, plus the number of surviving organisms for the antimicrobial combination was ≥ 2 log₁₀ less than the initial inoculum.

Results

All isolates carried bla_KPC-3 and genes encoding TEM-1 and SHV-11/-36; and were resistant to carbapenems (MIC at ≥ 8 μg/mL for ETP, MEM and IPM) and AMK (MIC 32 μg/mL) using broth microdilution. As monotherapy, none of the carbapenems nor AMK achieved and maintained bactericidal activity defined as ≥ 99.9% or > 3 log₁₀ killing. From time-kill studies, synergy was demonstrated for MEM and IPM in combination with AMK over the entire 24 h against all isolates. In addition, MEM and IPM with AMK achieved and maintained bactericidal activity (≥ 99.9% killing) at 24 h against 2 and 1 isolate(s), respectively. Bactericidal activity and synergy were not observed for ETP combinations.

Conclusions

The combination of MEM or IPM with AMK displayed synergistic activity against KPC-3-producing K. pneumoniae isolates.

Keywords

ESBL; Klebsiella pneumoniae; KPC; Carbapenemase; Time-kill; Meropenem; Amikacin; Imipenem; Ertapenem; Carbapenem; Synergy

Activity of tigecycline alone and in combination with colistin and meropenem against Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae strains by time-kill assay

Antibiotic combinations including tigecycline have not been studied against Klebsiella pneumoniae carbapenemase (KPC)-producing pathogens. Tigecycline alone and combined with colistin and meropenem was tested against eight genetically unrelated KPC-producing clinical strains of Enterobacteriaceae (four K. pneumoniae, two Escherichia coli, one Enterobacter cloacae and one Serratia marcescens) by time-kill assay. Tigecycline displayed a concentration-independent bacteriostatic activity in seven strains and bactericidal activity in one strain. Colistin showed bactericidal activity at 4× the minimum inhibitory concentration (MIC) in three strains and was bacteriostatic for the remaining strains and concentrations. Meropenem was bactericidal in three strains and bacteriostatic in five strains. The tigecycline+meropenem combination was not bactericidal against the four K. pneumoniae strains and was non-synergistic against all eight strains. Tigecycline+colistin was bactericidal against all strains at most time intervals and concentrations and was also synergistic at 1× and 2× MIC against most strains up to 4-8h and at 4× MIC up to 24 h against all strains. These findings suggest that, at most drug concentrations, tigecycline, colistin and meropenem as single agents do not exhibit efficient bactericidal activity against most of the KPC-producing strains. Tigecycline alone might be a therapeutic option for infections caused by KPC-producers when bacteriostatic activity is adequate or combined with colistin when bactericidal activity is necessary. Additional in vivo tests are warranted to assess better the killing kinetics of tigecycline combinations against KPC-producers.