Combination treatment with meropenem plus levofloxacin is synergistic against Pseudomonas aeruginosa infection in a murine model of pneumonia.

BACKGROUND: Meropenem plus levofloxacin treatment was shown to be a promising combination in our in vitro hollow fiber infection model. We strove to validate this finding in a murine Pseudomonas pneumonia model. METHODS: A dose-ranging study with meropenem and levofloxacin alone and in combination against Pseudomonas aeruginosa was performed in a granulocytopenic murine pneumonia model. Meropenem and levofloxacin were administered to partially humanize their pharmacokinetic profiles in mouse serum. Total and resistant bacterial populations were estimated after 24 hours of therapy. Pharmacokinetic profiling of both drugs was performed in plasma and epithelial lining fluid, using a population model. RESULTS: Meropenem and levofloxacin penetrations into epithelial lining fluid were 39.3% and 64.3%, respectively. Both monotherapies demonstrated good exposure responses. An innovative combination-therapy analytic approach demonstrated that the combination was statistically significantly synergistic (α = 2.475), as was shown in the hollow fiber infection model. Bacterial resistant to levofloxacin and meropenem was seen in the control arm. Levofloxacin monotherapy selected for resistance to itself. No resistant subpopulations were observed in any combination therapy arm. CONCLUSIONS: The combination of meropenem plus levofloxacin was synergistic, producing good bacterial kill and resistance suppression. Given the track record of safety of each agent, this combination may be worthy of clinical trial.

Pharmacodynamic evaluation of the activities of six parenteral vancomycin products available in the United States.

A recent report found that generic parenteral vancomycin products may not have in vivo efficacies equivalent to those of the innovator in a neutropenic murine thigh infection model despite having similar in vitro microbiological activities and murine serum pharmacokinetics. We compared the in vitro and in vivo activities of six of the parenteral vancomycin products available in the United States. The in vitro assessments for the potencies of the vancomycin products included MIC/minimal bactericidal concentration (MBC) determinations, quantifying the impact of human and murine serum on the MIC values, and time-kill studies. Also, the potencies of the vancomycin products were quantified with a biological assay, and the human and mouse serum protein binding rates for the vancomycin products were measured. The in vivo studies included dose-ranging experiments with the 6 vancomycin products for three isolates of Staphylococcus aureus in a neutropenic mouse thigh infection model. The pharmacokinetics of the vancomycin products were assessed in infected mice by population pharmacokinetic modeling. No differences were seen across the vancomycin products with regard to any in vitro evaluation. Inhibitory sigmoid maximal bacterial kill (Emax) modeling of the relationship between vancomycin dosage and the killing of the bacteria in mice in vivo yielded similar Emax and EC50 (drug exposure driving one-half Emax) values for bacterial killing. Further, there were no differences in the pharmacokinetic clearances of the 6 vancomycin products from infected mice. There were no important pharmacodynamic differences in the in vitro or in vivo activities among the six vancomycin products evaluated.

Interaction of drug- and granulocyte-mediated killing of Pseudomonas aeruginosa in a murine pneumonia model.

BACKGROUND: Killing of bacterial pathogens by granulocytes is a saturable process, as previously demonstrated. There is virtually no quantitative information about how granulocytes interact with antimicrobial chemotherapy to kill bacterial cells. METHODS: We performed a dose-ranging study with the aminoglycoside plazomicin against Pseudomonas aeruginosa ATCC27853 in a granulocyte-replete murine pneumonia model. Plazomicin was administered in a humanized fashion (ie, administration of decrementing doses 5 times over 24 hours, mimicking a human daily administration profile). Pharmacokinetic profiling was performed in plasma and epithelial lining fluid. All samples were simultaneously analyzed with a population model. Mouse cohorts were treated for 24 hours; other cohorts treated with the same therapy were observed for another 24 hours after therapy cessation, allowing delineation of the therapeutic effect necessary to reduce the bacterial burden to a level below the half-saturation point. RESULTS: The mean bacterial burden (±SD) at which granulocyte-mediated kill was half saturable was 2.45 × 10(6) ± 6.84 × 10(5) colony-forming units of bacteria per gram of tissue (CFU/g). Higher levels of plazomicin exposure reduced the bacterial burden to <5 log10 CFU/g, allowing granulocytes to kill an additional 1.0-1.5 log CFU/g over the subsequent 24 hours. CONCLUSIONS: For patients with large bacterial burdens (eg, individuals with ventilator-requiring hospital-acquired pneumonia), it is imperative to kill ≥2 log10 CFU/g early after treatment initiation, to allow the granulocytes to contribute optimally to bacterial clearance.