1264. Assessment of In Vivo Efficacy of CF-296 in addition to Vancomycin (VAN) and Daptomycin (DAP) against Staphylococcus aureus in the Neutropenic Murine Thigh Infection Model

Abstract Background CF-296 is a novel lysin in pre-clinical development for the treatment of methicillin-susceptible and methicillin-resistant Staphylococcus aureus infections, used in addition to standard of care antibiotics including VAN and DAP. We evaluated the in vivo efficacy of CF-296 alone and in addition to VAN and DAP against S. aureus. Methods Eight isolates (1 MSSA and 7 MRSA) were studied. Murine ICR MIC (100% serum) and human MIC (100% serum) for CF-296 ranged from 32-256 mg/L to 0.5-1 mg/L respectively. Broth microdilution MICs for DAP ranged from 0.5-1 mg/L while all isolates exhibited a VAN MIC of 1 mg/L. Neutropenic ICR mice were thigh inoculated with bacterial suspensions (107 CFU/mL). Mice were administered three monotherapy regimens subcutaneously (SC) or intravenously (IV): i) sub-therapeutic VAN, SC (i.e., a dose that yielded bacteria stasis or growth in order to evaluate further bacterial killing), ii) sub-therapeutic DAP, SC, or iii) CF-296 50 mg/kg, IV. Combination of sub-therapeutic VAN or DAP in addition to 5 escalating CF-296 doses ranging from 0.5 to 50 mg/kg were also examined. Control mice were vehicle-dosed. Efficacy was measured as the change in mean thigh bacterial density at 24h relative to 0h controls. Results Relative to starting inoculum (5.71 ± 0.27 at 0h), bacterial density in controls increased by +2.49 ± 0.98 log10 CFU/thigh across all 8 strains. On average, VAN, DAP, and CF-296 monotherapy resulted in +0.90 ± 1.21, +1.47 ± 0.80, and +0.87 ± 1.39 log10 CFU/thigh bacteria growth, respectively. In addition to VAN, escalating CF-296 exposures (0.5 – 50 mg/kg) resulted in an augmented dose-response, ranging from bacterial reduction of -0.26 ± 1.10 (with addition of CF-296 0.5 mg/kg) to -1.01 ± 0.41 log10 CFU/thigh (with addition of CF-296 50 mg/kg). Similarly, escalating CF-296 exposures in addition to DAP resulted in an augmented dose-response, ranging from bacterial density of +0.80 ± 1.19 to -0.72 ± 0.59 log10 CFU/thigh. Conclusion Compared with 24h control, VAN, DAP, and CF-296 alone displayed modest CFU reduction while CF-296 synergized with VAN and DAP to cause further bacterial killing highlighting a potential role for CF-296 adjunctive therapy against MSSA and MRSA isolates. Disclosures Cara Cassino, MD, ContraFect Corporation (Employee)ContraFect Corporation (Employee) Dario Lehoux, PhD, ContraFect Corporation (Consultant) Raymond Schuch, PhD, ContraFect Corporation (Employee) David P. Nicolau, PharmD, Cepheid (Other Financial or Material Support, Consultant, speaker bureau member or has received research support.)Merck & Co., Inc. (Consultant, Grant/Research Support, Speaker’s Bureau)Wockhardt (Grant/Research Support)

Download Full-text

1296. Efficacy of Human-Simulated Exposures of Meropenem/Vaborbactam (MVB) and Meropenem (MEM) against OXA-48 β-lactamase-producing Enterobacterales in the Neutropenic Murine Thigh Infection Model

Open Forum Infectious Diseases ◽

10.1093/ofid/ofaa439.1479 ◽

2020 ◽

Vol 7 (Supplement_1) ◽

pp. S663-S663

Author(s):

Christian M Gill ◽

Tomefa E Asempa ◽

David P Nicolau

Keyword(s):

Surrogate Marker ◽

Hydrolytic Activity ◽

Infection Model ◽

Bacterial Reduction ◽

Research Support ◽

Serious Infections ◽

The Mean ◽

Change In Mean ◽

Poor Efficacy

Abstract Background OXA-48 exhibits variable hydrolytic activity toward carbapenems, with imipenem and meropenem MICs, though increased, often reporting within the ‘susceptible’ or ‘intermediate’ ranges defined by CLSI and EUCAST. Although vaborbactam (VAB) does not enhance MEM activity against OXA-48, ~ 1/3 of OXA-48-producing Enterobacterales will test susceptible to MVB due to its higher breakpoint. Clinical implications of this discordance warrant investigation. Methods 26 isolates harboring OXA-48 (n=24) and KPC (n=2) were evaluated in the neutropenic murine thigh model. MICs were determined in triplicate per CLSI. Human-simulated regimens of MVB (simulating doses of 2-2 g IV q 8 hours (h) over 3 h) and MEM (2 g IV q 8 h over 3 h) were administered resulting in similar f%T >MIC and fAUC as humans for MEM and VAB, respectively. Mice received MVB, MEM, or sham control for 24 h. Efficacy was assessed on the resulting overall change in mean± SD log10 CFU/thigh as well as the achievement of ≥ 1 log10 reduction as an established surrogate marker predictive of success for serious infections. Results MVB and MEM MICs ranged from 1- 64 and 2 - > 64 mg/L, respectively. Relative to 0 h control, the mean bacterial growth (mean ± SD, CFU/thigh) at 24 h in the untreated control mice was 2.69 ± 1.31. As anticipated for KPCs, MVB resulted in a mean bacterial reduction ≥ 1 log10 (-1.10 ± 0.26), whereas growth was observed on MEM (+1.45 ± 0.88). For all OXA-48 isolates, MVB resulted in variable bacterial densities ranging from -2.54 to +2.68, similarly MEM resulted in -2.18 to +2.66. Addition of vaborbactam did not enhance MEM activity for any isolate. For isolates with MVB MICs ≥ 16 (n=5), 8 (n=5, EUCAST breakpoint), 4 (n=9, CLSI breakpoint), and ≤ 2 (n=5) mg/L, 0%, 0%, 44%, and 60% of isolates treated with MVB or MEM achieved the target reduction of ≥ 1 log10 kill, respectively. Conclusion Across the range of MICs evaluated, MVB and MEM humanized exposures in vivo resulted in similar reductions and growth in bacterial density for OXA-48-producing Enterobacterales. Moreover, these data highlight the poor efficacy of MVB for OXA-48 defined as susceptible using the current EUCAST and CLSI susceptibility criterion. Caution is therefore warranted when treating Enterobacterales testing susceptible to MVB without the genotypic profile. Disclosures David P. Nicolau, PharmD, Cepheid (Other Financial or Material Support, Consultant, speaker bureau member or has received research support.)Merck & Co., Inc. (Consultant, Grant/Research Support, Speaker’s Bureau)Wockhardt (Grant/Research Support)

Download Full-text

Mechanism-Based Pharmacokinetic/Pharmacodynamic Modeling of Aerosolized Colistin in a Mouse Lung Infection Model

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01965-17 ◽

2017 ◽

Vol 62 (3) ◽

Cited By ~ 4

Author(s):

Yu-Wei Lin ◽

Qi Tony Zhou ◽

Mei-Ling Han ◽

Nikolas J. Onufrak ◽

Ke Chen ◽

...

Keyword(s):

Critically Ill ◽

Critically Ill Patients ◽

Pharmacodynamic Modeling ◽

Mouse Lung ◽

Infection Model ◽

Bacterial Reduction ◽

Bacterial Killing ◽

Deterministic Simulation ◽

Dosage Regimens

ABSTRACTOptimized dosage regimens of aerosolized colistin (as colistin methanesulfonate [CMS]) are urgently required to maximize bacterial killing against multidrug-resistant Gram-negative bacteria while minimizing toxicity. This study aimed to develop a mechanism-based pharmacokinetic (PK)/pharmacodynamic (PD) model (MBM) for aerosolized colistin based upon PK/PD data in neutropenic infected mice and to perform a deterministic simulation with the PK of aerosolized colistin (as CMS) in critically ill patients.In vivotime-kill experiments were carried out with three different strains ofPseudomonas aeruginosa. An MBM was developed in S-ADAPT and evaluated by assessing its ability to predict the PK/PD index associated with efficacy in mice. A deterministic simulation with human PK data was undertaken to predict the efficacy of current dosage regimens of aerosolized colistin in critically ill patients. In the final MBM, the total bacterial population for each isolate consisted of colistin-susceptible and -resistant subpopulations. The antimicrobial efficacy of aerosolized colistin was best described by a sigmoidalEmaxmodel whereby colistin enhanced the rate of bacterial death. Deterministic simulation with human PK data predicted that an inhalational dosage regimen of 60 mg colistin base activity (CBA) every 12 h is needed to achieve a ≥2-log10bacterial reduction (as the number of CFU per lung) in critically ill patients at 24 h after commencement of inhaled therapy. In conclusion, the developed MBM is a useful tool for optimizing inhalational dosage regimens of colistin. Clinical studies are warranted to validate and refine our MBM for aerosolized colistin.

Download Full-text

In VivoPharmacodynamic Target Assessment of Delafloxacin against Staphylococcus aureus, Streptococcus pneumoniae, and Klebsiella pneumoniae in a Murine Lung Infection Model

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00647-16 ◽

2016 ◽

Vol 60 (8) ◽

pp. 4764-4769 ◽

Cited By ~ 26

Author(s):

Alexander J. Lepak ◽

David R. Andes

Keyword(s):

Staphylococcus Aureus ◽

Single Dose ◽

Streptococcus Pneumoniae ◽

Klebsiella Pneumoniae ◽

Dose Response ◽

Lung Infection ◽

Infection Model ◽

Content Type ◽

Murine Lung

ABSTRACTDelafloxacin is a broad-spectrum anionic fluoroquinolone under development for the treatment of bacterial pneumonia. The goal of the study was to determine the pharmacokinetic/pharmacodynamic (PK/PD) targets in the murine lung infection model forStaphylococcus aureus,Streptococcus pneumoniae, andKlebsiella pneumoniae. Four isolates of each species were utilized forin vivostudies: forS. aureus, one methicillin-susceptible and three methicillin-resistant isolates;S. pneumoniae, two penicillin-susceptible and two penicillin-resistant isolates;K. pneumoniae, one wild-type and three extended-spectrum beta-lactamase-producing isolates. MICs were determined using CLSI methods. A neutropenic murine lung infection model was utilized for all treatment studies, and drug dosing was by the subcutaneous route. Single-dose plasma pharmacokinetics was determined in the mouse model after administration of 2.5, 10, 40, and 160 mg/kg. Forin vivostudies, 4-fold-increasing doses of delafloxacin (range, 0.03 to 160 mg/kg) were administered every 6 h (q6h) to infected mice. Treatment outcome was measured by determining organism burden in the lung (CFU counts) at the end of each experiment (24 h). The Hill equation for maximum effect (Emax) was used to model the dose-response data. The magnitude of the PK/PD index, the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC), associated with net stasis and 1-log kill endpoints was determined in the lung model for all isolates. MICs ranged from 0.004 to 1 mg/liter. Single-dose PK parameter ranges include the following: for maximum concentration of drug in serum (Cmax), 2 to 70.7 mg/liter; AUC from 0 h to infinity (AUC0–∞), 2.8 to 152 mg · h/liter; half-life (t1/2), 0.7 to 1 h. At the start of therapy mice had 6.3 ± 0.09 log10CFU/lung. In control mice the organism burden increased 2.1 ± 0.44 log10CFU/lung over the study period. There was a relatively steep dose-response relationship observed with escalating doses of delafloxacin. Maximal organism reductions ranged from 2 log10to more than 4 log10. The median free-drug AUC/MIC magnitude associated with net stasis for each species group was 1.45, 0.56, and 40.3 forS. aureus,S. pneumoniae, andK. pneumoniae, respectively. AUC/MIC targets for the 1-log kill endpoint were 2- to 5-fold higher. Delafloxacin demonstratedin vitroandin vivopotency against a diverse group of pathogens, including those with phenotypic drug resistance to other classes. These results have potential relevance for clinical dose selection and evaluation of susceptibility breakpoints for delafloxacin for the treatment of lower respiratory tract infections involving these pathogens.

Download Full-text

Serine-Aspartate Repeat Protein D Increases Staphylococcus aureus Virulence and Survival in Blood

Infection and Immunity ◽

10.1128/iai.00559-16 ◽

2016 ◽

Vol 85 (1) ◽

Cited By ~ 9

Author(s):

Fatemeh Askarian ◽

Satoshi Uchiyama ◽

J. Andrés Valderrama ◽

Clement Ajayi ◽

Johanna U. E. Sollid ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Ex Vivo ◽

Innate Immune ◽

Human Neutrophils ◽

Infection Model ◽

Bacterial Survival ◽

Bacterial Killing ◽

Content Type ◽

Repeat Protein

ABSTRACT Staphylococcus aureus expresses a panel of cell wall-anchored adhesins, including proteins belonging to the microbial surface components recognizing adhesive matrix molecule (MSCRAMM) family, exemplified by the serine-aspartate repeat protein D (SdrD), which serve key roles in colonization and infection. Deletion of sdrD from S. aureus subsp. aureus strain NCTC8325-4 attenuated bacterial survival in human whole blood ex vivo, which was associated with increased killing by human neutrophils. Remarkably, SdrD was able to inhibit innate immune-mediated bacterial killing independently of other S. aureus proteins, since addition of recombinant SdrD protein and heterologous expression of SdrD in Lactococcus lactis promoted bacterial survival in human blood. SdrD contributes to bacterial virulence in vivo, since fewer S. aureus subsp. aureus NCTC8325-4 ΔsdrD bacteria than bacteria of the parent strain were recovered from blood and several organs using a murine intravenous infection model. Collectively, our findings reveal a new property of SdrD as an important key contributor to S. aureus survival and the ability to escape the innate immune system in blood.

Download Full-text

Sequential Evolution of Vancomycin-Intermediate Resistance Alters Virulence in Staphylococcus aureus: Pharmacokinetic/Pharmacodynamic Targets for Vancomycin Exposure

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02657-15 ◽

2015 ◽

Vol 60 (3) ◽

pp. 1584-1591 ◽

Cited By ~ 9

Author(s):

Justin R. Lenhard ◽

Tanya Brown ◽

Michael J. Rybak ◽

Calvin J. Meaney ◽

Nicholas B. Norgard ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Galleria Mellonella ◽

Infection Model ◽

Bacterial Reduction ◽

Accessory Gene ◽

Time Curve ◽

Bacterial Killing ◽

Unbound Fraction ◽

Content Type ◽

Intermediate Resistance

Staphylococcus aureuspossesses exceptional virulence and a remarkable ability to adapt in the face of antibiotic therapy. We examined thein vitroevolution ofS. aureusin response to escalating vancomycin exposure by evaluating bacterial killing and the progression of resistance. A hollow-fiber infection model was utilized to simulate human doses of vancomycin increasing from 0.5 to 4 g every 12 h (q12h) versus a high inoculum (108CFU/ml) of methicillin-resistantS. aureus(MRSA) USA300 and USA400. Host-pathogen interactions usingGalleria mellonellaand accessory gene regulator (agr) expression were studied in serially obtained isolates. In both USA300 and USA400 MRSA isolates, vancomycin exposure up to 2 g q12h resulted in persistence and regrowth, whereas 4 g administered q12h achieved sustained killing against both strains. As vancomycin exposure increased from 0.5 to 2 g q12h, the bacterial population shifted toward vancomycin-intermediate resistance, and collateral increases in the MICs of daptomycin and televancin were observed over 10 days. Guideline-recommended exposure of a ratio of the area under the concentration-time curve for the free, unbound fraction of the drug to the MIC (fAUC/MIC ratio) of 200 displayed a 0.344-log bacterial reduction in area, whereasfAUC/MICs of 371 and 554 were needed to achieve 1.00- and 2.00-log reductions in area, respectively. The stepwise increase in resistance paralleled a decrease inG. mellonellamortality (P= 0.021) and a gradual decline of RNAIII expression over 10 days. Currently recommended doses of vancomycin resulted in amplification of resistance and collateral damage to other antibiotics. Decreases inagrexpression and virulence during therapy may be an adaptive mechanism ofS. aureuspersistence.

Download Full-text

Antibacterial Efficacy of EravacyclineIn Vivoagainst Gram-Positive and Gram-Negative Organisms

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00366-16 ◽

2016 ◽

Vol 60 (8) ◽

pp. 5001-5005 ◽

Cited By ~ 28

Author(s):

Marguerite L. Monogue ◽

Abrar K. Thabit ◽

Yukihiro Hamada ◽

David P. Nicolau

Keyword(s):

Cumulative Dose ◽

Dose Response ◽

Bacterial Count ◽

Infection Model ◽

Gram Positive ◽

Bacterial Killing ◽

Gram Negative ◽

Content Type

ABSTRACTMembers of the tetracycline class are frequently classified as bacteriostatic. However, recent findings have demonstrated an improved antibacterial killing profile, often achieving ≥3 log10bacterial count reduction, when such antibiotics have been given for periods longer than 24 h. We aimed to study this effect with eravacycline, a novel fluorocycline, given in an immunocompetent murine thigh infection model over 72 h against two methicillin-resistantStaphylococcus aureus(MRSA) isolates (eravacycline MICs = 0.03 and 0.25 μg/ml) and threeEnterobacteriaceaeisolates (eravacycline MICs = 0.125 to 0.25 μg/ml). A humanized eravacycline regimen, 2.5 mg/kg of body weight given intravenously (i.v.) every 12 h (q12h), demonstrated progressively enhanced activity over the 72-h study period. A cumulative dose response in which bacterial density was reduced by more than 3 log10CFU at 72 h was noted over the study period in the two Gram-positive isolates, and eravacycline performed similarly to comparator antibiotics (tigecycline, linezolid, and vancomycin). A cumulative dose response with eravacycline and comparators (tigecycline and meropenem) over the study period was also observed in the Gram-negative isolates, although more variability in bacterial killing was observed for all antibacterial agents. Overall, a bacterial count reduction of ≥3 log was achieved in one of the three isolates with both eravacycline and tigecycline, while meropenem achieved a similar endpoint against two of the three isolates. Bactericidal activity is typically definedin vitroover 24 h; however, extended regimen studiesin vivomay demonstrate an improved correlation with clinical outcomes by better identification of antimicrobial effects.

Download Full-text

Humanized Exposures of Cefiderocol, a Siderophore Cephalosporin, Display Sustained in vivo Activity against Siderophore-Resistant Pseudomonas aeruginosa

Pharmacology ◽

10.1159/000487441 ◽

2018 ◽

Vol 101 (5-6) ◽

pp. 278-284 ◽

Cited By ~ 13

Author(s):

Islam M. Ghazi ◽

Marguerite L. Monogue ◽

Masakatsu Tsuji ◽

David P. Nicolau

Keyword(s):

Pseudomonas Aeruginosa ◽

Bacterial Density ◽

Infection Model ◽

Test Panel ◽

In Vivo Efficacy ◽

Preclinical Data ◽

Variable Activity ◽

Susceptibility Profiles ◽

Phenotypic Susceptibility

We evaluated the in vivo efficacy of humanized exposures of cefiderocol, a novel siderophore cephalosporin, against a test panel of P. aeruginosa (PSA) previously shown to develop resistance to 2 preclinical candidate siderophores (MB-1 and SMC-3176). In the thigh infection model, the PSA bacterial density in untreated controls grew from 5.54 ± 0.23 to 8.68 ± 0.57 log10 CFU over 24 h. The humanized cefiderocol exposure resulted in >1 log10 CFU reduction in all 8 isolates, while MB-1 and SMC-3176 exhibited variable activity similar to that previously reported. Humanized exposures of cefepime and levofloxacin, acting as positive antimicrobial controls displayed activity consistent with that of the bacterial phenotypic susceptibility profiles. Cefiderocol manifested in vivo efficacy against all PSA isolates including those resistant to cefepime and levofloxacin in contrast to its predecessor siderophore compounds. These preclinical data are supportive of further evaluation of cefiderocol in the treatment of P. aeruginosa.

Download Full-text

Comparative Efficacies of Human Simulated Exposures of Tedizolid and Linezolid against Staphylococcus aureus in the Murine Thigh Infection Model

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00122-12 ◽

2012 ◽

Vol 56 (8) ◽

pp. 4403-4407 ◽

Cited By ~ 28

Author(s):

R. A. Keel ◽

P. R. Tessier ◽

J. L. Crandon ◽

D. P. Nicolau

Keyword(s):

Staphylococcus Aureus ◽

Bacterial Density ◽

Infection Model ◽

Immunocompetent Mouse ◽

Time Curve ◽

Free Concentration ◽

Content Type ◽

The Mean

ABSTRACTTedizolid (formally torezolid) is an expanded-spectrum oxazolidinone with enhancedin vitropotency against Gram-positive pathogens, including methicillin-susceptibleStaphylococcus aureus(MSSA) and methicillin-resistantS. aureus(MRSA). The efficacies of human simulated exposures of tedizolid and linezolid againstS. aureusin an immunocompetent mouse thigh model over 3 days were compared. Four strains of MRSA and one of MSSA with tedizolid and linezolid MICs ranging from 0.25 to 0.5 and from 2 to 4 μg/ml, respectively, were utilized. Tedizolid or linezolid was administered in a regimen simulating a human steady-state 24-h area under the free concentration-time curve of 200 mg every 24 h (Q24) or 600 mg Q12, respectively. Thighs were harvested after 4, 8, 12, 24, 36, 48, and 72 h, and efficacy was determined by the change in bacterial density. The mean bacterial density in control mice increased over the 3-day period. After 24 h of treatment, a reduction in bacterial density of ≥1 log CFU was observed for both the tedizolid and linezolid treatments. Antibacterial activity was enhanced for both agents with a reduction of ≥2.6 log CFU after 72 h of treatment. Any statistically significant differences (P≤ 0.05) in efficacy between the agents were transient and did not persist throughout the 72-h treatment period. The tedizolid and linezolid regimens demonstrated similarin vivoefficacies against theS. aureusisolates tested. Both agents were bacteriostatic at 24 h and bactericidal on the third day of treatment. These data support the clinical utility of tedizolid for skin and skin structure infections caused byS. aureus, as well as the bactericidal activity of the oxazolidinones after 3 days of treatment.

Download Full-text

In Vivo Efficacy of a Novel Oxazolidinone Compound in Two Mouse Models of Infection

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.01567-06 ◽

2007 ◽

Vol 51 (9) ◽

pp. 3434-3436 ◽

Cited By ~ 12

Author(s):

Charles J. Gill ◽

George K. Abruzzo ◽

Amy M. Flattery ◽

Andrew S. Misura ◽

Ken Bartizal ◽

...

Keyword(s):

Staphylococcus Aureus ◽

Mouse Models ◽

Infection Model ◽

In Vivo Efficacy ◽

Methicillin Resistant

ABSTRACT A novel oxazolidinone, AM 7359, was evaluated in two mouse models of Staphylococcus aureus infection. AM 7359 and linezolid were equally efficacious in a methicillin-susceptible S. aureus organ burden model and a methicillin-resistant S. aureus localized infection model. However, AM 7359 was eightfold more efficacious than linezolid against a linezolid- and methicillin-resistant S. aureus strain in this localized (thigh) infection model.

Download Full-text

1241. In Vivo Efficacy of Meropenem Against Metallo-ß-Lactamase (MBL)-Harboring Pseudomonas aeruginosa and Correlation to In Vitro Susceptibility Upon Addition of EDTA

Open Forum Infectious Diseases ◽

10.1093/ofid/ofab466.1433 ◽

2021 ◽

Vol 8 (Supplement_1) ◽

pp. S710-S710

Author(s):

Abigail K Kois ◽

Tomefa E Asempa ◽

David P Nicolau

Keyword(s):

Infection Model ◽

Bacterial Killing ◽

In Vitro Susceptibility ◽

In Vivo Efficacy ◽

Treatment Groups ◽

Emax Model ◽

Mueller Hinton ◽

Pharmacodynamic Profile

Abstract Background Prior investigations evaluating the predictive value of zinc-depleted media for MBL-susceptibility testing have focused on Enterobacterales. Therein, bacterial killing observed with meropenem (MEM) in vivo was concordant with its pharmacodynamic profile using MIC values determined in zinc-depleted media compared with conventional cation-adjusted Mueller-Hinton broth (CAMHB). This study aims to evaluate the exposure-response relationship of MEM against VIM- and NDM-harboring P. aeruginosa (PSA) using the murine thigh infection model and zinc-depleted MICs. Methods MBL-harboring PSA isolates (VIM n=11; NDM n=10) were tested both in vivo (neutropenic murine thigh infection model) and in vitro (broth microdilution). The 24h murine thigh study was conducted with treatment groups receiving a humanized MEM 2g q8h (3h infusion) dose. Six different zinc-limited media were prepared by the addition of EDTA at concentrations ranging from 3 to 300 mg/L to CAMHB. MEM MICs were determined in triplicate in conventional CAMHB and zinc-limited media. Time > MIC values (generated in each zinc-depleted media) were then plotted against the change in 24h bacterial density count in an Emax model. Results Average 0 h bacterial densities were 5.21 ± 0.40 and 5.13 ± 0.81 log10 CFU/thigh for NDM and VIM isolates, respectively. MEM resulted in -0.09 CFU reduction to +3.69 CFU growth against NDM isolates. MEM resulted in -2.59 CFU reduction to +4.81 CFU growth against VIM isolates. All MEM MICs in conventional CAMHB were >64 µg/mL for NDM and ranged from 8 to >64 µg/mL for VIM isolates. Increasing EDTA concentrations resulted in several-fold MIC reductions and on average, a larger magnitude of reduction was observed among VIM- (6-fold) compared with NDM-harboring PSA (4-fold) in CAMHB-EDTA 300 mg/L relative to CAMHB. For both NDM- and VIM-harboring PSA, an Emax model with MICs generated in CAMHB+EDTA 30 mg/L (r2 = 0.88) provided the highest correlation with MEM in vivo activity compared with CAMHB (r2 = 0.55). Conclusion Results indicate that MIC values generated in conventional CAMHB do not appropriately characterize the in vivo efficacy of meropenem against MBL-harboring PSA, and addition of EDTA (30 mg/L) to CAMHB appears to be a viable option for in vitro testing of these organisms. Disclosures David P. Nicolau, PharmD, Abbvie, Cepheid, Merck, Paratek, Pfizer, Wockhardt, Shionogi, Tetraphase (Other Financial or Material Support, I have been a consultant, speakers bureau member, or have received research funding from the above listed companies.)

Download Full-text