<i>In Vivo</i>
            Comparison of CXA-101 (FR264205) with and without Tazobactam versus Piperacillin-Tazobactam Using Human Simulated Exposures against Phenotypically Diverse Gram-Negative Organisms

Negligible in vivo growth of enterococci and high-level dispersion of data have led to inaccurate estimations of antibiotic pharmacodynamics (PD). Here we improved an in vivo model apt for PD studies by optimizing the in vitro culture conditions for enterococci. The PD of vancomycin (VAN), ampicillin-sulbactam (SAM), and piperacillin-tazobactam (TZP) against enterococci were determined in vivo, comparing the following different conditions of inoculum preparation: aerobiosis, aerobiosis plus mucin, and anaerobiosis plus mucin. Drug exposure was expressed as the ratio of the area under the concentration-time curve for the free, unbound fraction of the drug to the MIC (fAUC/MIC) (VAN) or the time in a 24-h period that the drug concentration for the free, unbound fraction exceeded the MIC under steady-state pharmacokinetic conditions (fT >MIC ) (SAM and TZP) and linked to the change in log 10 CFU/thigh. Only anaerobiosis plus mucin enhanced the in vivo growth, yielding significant PD parameters with all antibiotics. In conclusion, robust in vivo growth of enterococci was crucial for better determining the PD of tested antibacterial agents, and this was achieved by optimizing the procedure for preparing the inoculum. Enterococci are commensal organisms in the gastrointestinal tracts of many species, from insects to humans (1), but are also the third leading cause of hospital infections (2, 3). They display intrinsic and acquired resistance to almost all antibiotics in clinical use, and no single agent is able to kill more than 3 log 10 CFU/g in vivo (4). Animal models of infection are invaluable tools for anti-infective pharmacology, and numerous in vivo enterococcal models have been used to test old and new drugs, but their validation for assessing the efficacy of antimicrobial agents is frequently not reported (5). The enterococcal endocarditis rabbit model is perhaps used the most, but it is also more expensive, cumbersome, and centered on a tissue with complex pharmacokinetics (i.e., cardiac valves), limiting its relevance for other systemic infections (6). Additionally, the usual lack of a full doseresponse curve hinders the determination of pharmacokinetic/ pharmacodynamic (PK/PD) indices necessary to translate the results to humans (5, 7). Moreover, the bacterial growth in all enterococcal models is either not quantified (e.g., peritonitis model) (8), poor (ϳ1 log 10 CFU/g), or even negative (e.g., thigh infection) (9, 10), and the variability is high (e.g., rabbit endocarditis models) (11), particularly with vancomycin (VAN)-resistant enterococcus (VRE) strains (12). Negligible growth and high-level dispersion may lead to inaccurate estimations of antibiotic PD, as has been the case with daptomycin (13).We optimized the in vitro culture conditions for enterococci by using anaerobic incubation and mucin supplementation, aiming to enhance the in vivo growth of vancomycin-susceptible enterococcus (VSE) and VRE strains and to determine its impact on the PD of three antibiotics: VAN, ampicillin-sulbactam (SAM), an...

Section: Methodsmentioning

confidence: 99%

An Optimized Mouse Thigh Infection Model for Enterococci and Its Impact on Antimicrobial Pharmacodynamics

Rodríguez

Agudelo

González

et al. 2015

“…The regimen chosen was based on a previous pharmacokinetic study that established a murine TZP exposure similar to that of 4.5 g given every 6 h in humans (3). Target exposures were defined as similar by the free time above MIC (f TϾMIC) from 0 to 24 h using a protein binding value of 20% for both mice and humans (6)(7)(8)(9). Initial CFU burden was assessed prior to dose administration (0 h) for each isolate as mice (n ϭ 6) were euthanized and their lungs harvested.…”

mentioning

confidence: 99%

In Vitro-In Vivo Discordance with Humanized Piperacillin-Tazobactam Exposures against Piperacillin-Tazobactam-Resistant/Pan-β-Lactam-Susceptible Klebsiella pneumoniae Strains

Stainton

Monogue

Nicolau

2017

Recent findings have identified Klebsiella pneumoniae strains that are pan-␤-lactam susceptible (PBL-S) but piperacillin-tazobactam resistant (TZP-R) in vitro. We assessed the efficacy of a humanized exposure of piperacillin-tazobactam (TZP) against 12 TZP-R/PBL-S K. pneumoniae isolates in an immunocompromised murine lung infection model. Discordance between the in vitro resistance profile and the in vivo efficacy of human-simulated TZP exposures against this phenotypic profile was observed. Additional studies are required to define the clinical implications of these TZP-R/PBL-S strains.KEYWORDS piperacillin-tazobactam, Klebsiella pneumoniae, antibiotic resistance P iperacillin-tazobactam (TZP) continues to be a workhorse antimicrobial in hospitals globally due to its broad coverage, particularly against Pseudomonas and Enterobacteriaceae species. As multidrug-resistant (MDR) Gram-negative pathogens evolve, the potency of the most frequently used agents, including TZP, deteriorates (1).Previously we identified Escherichia coli and Klebsiella pneumoniae strains resistant to TZP but pan-susceptible to other ␤-lactams (TZP-R/PBL-S), including cephalosporins, carbapenems, and monobactams in vitro (2, 3). The mechanism behind this resistance profile is thought to be attributable to a porin mutation, although the contribution of TEM-1 ␤-lactamase may also play a role (4). While further delineation of the mechanism is required, insights regarding the clinical consequences of this novel phenotype are of interest due to the extensive use of empirical TZP in debilitated hospitalized patients. In an attempt to better understand the clinical implications of this resistant phenotype, an initial in vivo murine study was conducted using humanized TZP exposures and E. coli isolates displaying this resistant phenotype (3). Interestingly, this study demonstrated an overt in vitro/in vivo discordance, as humanized TZP exposures were found to produce substantive killing, despite phenotypically and genotypically confirmed resistance. Herein, we sought to characterize the efficacy of the humanized TZP regimen against K. pneumoniae displaying this novel phenotype to gain new insights regarding treatment challenges for this important nosocomial pathogen.Sixteen K. pneumoniae strains, 12 displaying the TZP-R/PBL-S phenotype and 4 the TZP-susceptible (TZP-S) phenotype, collected during the conduct of the previously noted surveillance program, were included in the current investigation (2). Prior to the in vivo studies, the TZP MICs were reconfirmed in triplicate using broth microdilution methods according to the 2016 Clinical and Laboratory Standards Institute guidelines

“…The half-life of tazobactam was approximately 10 min. We found no earlier reference to tazobactam pharmacokinetics in mice, except for the studies by Fournier et al (14) and Bulik et al (8). However, in the study by Fournier et al, no specific pharmacokinetic data are provided other than a concentration-time plot; in the study by Bulik et al, the authors simulated human pharmacokinetics in their specific model, so the results cannot be directly compared.…”

Section: Discussionmentioning

confidence: 46%

“…injections were utilized, while most previous in vivo studies used subcutaneous doses. Of note, we did not find any pharmacokinetic interaction between tazobactam and ceftolozane, as was alluded to in the preliminary study by Bulik et al (8). One possible reason might be that the doses used in our study were low enough not to show any; in the study by Bulik et al, the dosing regimens were adjusted by lowering the dose but giving doses more often to account for drug interactions.…”

Section: Discussionmentioning

confidence: 67%

“…In addition, it is not clear whether pharmacokinetic interactions exist between cephalosporins and tazobactam. In one earlier, limited study, such a pharmacokinetic interaction was observed between these two compounds (8) in mice, although it was not observed in men (9). Thus, the primary objectives of this study were to evaluate the pharmacokinetic profiling of ceftolozane and tazobactam in the mouse plasma and ELF and to assess potential drug interactions using a neutropenic murine thigh or lung infection model.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Plasma and Epithelial Lining Fluid Pharmacokinetics of Ceftolozane and Tazobactam Alone and in Combination in Mice

Melchers

Mavridou

Seyedmousavi

et al. 2015

cCeftolozane is a new cephalosporin with activity against Gram-negative and Gram-positive microorganisms. However, the compound is susceptible to degradation by extended-spectrum beta-lactamases (ESBLs). Tazobactam is an ESBL inhibitor and is combined with ceftolozane to broaden its activity. Surprisingly, although tazobactam has been available for over 20 years, few if any reliable data exist on the tazobactam pharmacokinetic (PK) properties in mice. To evaluate the PK and pharmacodynamic (PD) relationships in mice, the PK properties of tazobactam and ceftolozane were extensively investigated. Thigh-infected neutropenic CD-1 mice were injected intraperitoneally with a single 0.1-ml dose containing ceftolozane, tazobactam, or both compounds. Ceftolozane was applied in 2-fold-increasing doses of 4 mg/kg of body weight to 64 mg/kg alone or in combination. Tazobactam was combined in reverse doses (thus, 64/4 mg/kg, 32/8 mg/kg, etc.) (n ‫؍‬ 2 per time point). In separate validation experiments, ceftolozane-tazobactam was given alone or in combination at 32/8 mg/kg and 8/32 mg/kg (n ‫؍‬ 4 per time point). Plasma samples (one per mouse) and bronchoalveolar lavage samples were collected at up to 12 time points until 6 h after administration. There were no significant differences in the ceftolozane and tazobactam PK alone versus combined, indicating no PK interaction. The PKs were linear and dose proportional for both compounds and showed a good penetration in the epithelial lining fluid. The estimated mean (standard deviation) half-life of ceftolozane was 0.287 h (0.031 h), and that of tazobactam was 0.176 h (0.026), and the V was 0.43 liter/kg and 1.14 liter/kg, respectively. The estimates of tazobactam parameters can also be used to (re)interpret PD data. Ceftolozane is a novel cephalosporin with activity against Pseudomonas aeruginosa and other Gram-negative microorganisms. However, the compound is susceptible to degradation by extended-spectrum beta-lactamases (ESBLs); therefore, the compound is combined with tazobactam, a potent beta-lactamase inhibitor, to broaden its activity. The combination had been shown to be active in vitro against a wide variety of microorganisms with different resistance mechanisms (1-5). The combination has also been shown to be active in vivo, in particular in animal models, against both P. aeruginosa and Enterobacteriaceae (6, 7). However, the pharmacodynamics of tazobactam in vivo have not been fully identified, despite being available for over 20 years in the combination piperacillin-tazobactam. Indeed few, if any, reliable data exist on the tazobactam pharmacokinetic (PK) properties in mice, including its penetration in lung epithelial lining fluid (ELF), precluding pharmacodynamic analyses. In addition, it is not clear whether pharmacokinetic interactions exist between cephalosporins and tazobactam. In one earlier, limited study, such a pharmacokinetic interaction was observed between these two compounds (8) in mice, although it was not observed in men (9). Thus, the primary object...