In Vitro Pharmacodynamics of Simulated Pulmonary Exposures of Tigecycline Alone and in Combination against Klebsiella pneumoniae Isolates Producing a KPC Carbapenemase

Multidrug-resistant Klebsiella pneumoniae strains that produce a serine carbapenemase (KPC) are emerging worldwide, with few therapeutic options that retain consistent susceptibility. The objective of this study was to determine the effect of combination therapy with tigecycline versus tigecycline alone against KPC-producing isolates (KPC isolates). An in vitro pharmacodynamic model was used to simulate adult steady-state epithelial lining fluid concentrations of tigecycline (50 mg every 12 h) given alone and in combination with either meropenem (2 g by 3-hour infusion every 8 h) or rifampin (600 mg every 12 h). Five KPC isolates with various phenotypic profiles were exposed over 48 h. Time-kill curves were constructed, and the areas under the bacterial killing and regrowth curves (AUBCs) were calculated. No regimens tested were able to maintain bactericidal reductions in CFU over 48 h. The AUBCs for tigecycline and meropenem monotherapies at 48 h ranged from 375.37 to 388.11 and from 348.62 to 383.83 (CFU-h/ml), respectively. The combination of tigecycline plus meropenem significantly reduced the AUBCs at 24 and 48 h for isolates with tigecycline MICs of <= 2 mu g/ml and meropenem MICs of <= 16 mu g/ml (P < 0.001) but added no additional activity when the meropenem MIC was 64 mu g/ml (P = 0.5). Rifampin provided no additional reduction in CFU or AUBC over tigecycline alone (P = 0.837). The combination of tigecycline with high-dose, prolonged-infusion meropenem warrants further study as a potential treatment option for these multidrug-resistant organisms.