Population pharmacokinetics of moxifloxacin in plasma and bronchial secretions in patients with bronchopneumonia

Objective: Our objective was to construct a population pharmacokinetic model for moxifloxacin disposition in plasma and bronchial secretions in patients with severe bronchopneumonia who were mechanically ventilated. Methods: Seventeen patients receiving 400 mg moxifloxacin intravenously daily were enrolled in this multi-center, prospective, open-label study. Blood and bronchial samples were collected on days 1 and 4. The population pharmacokinetic modeling was performed with NONMEM. Results: Moxifloxacin rapidly appeared in bronchial secretions and reached maximum concentrations within 1 to 2 hours. The concentrations achieved in plasma and bronchial secretions showed parallel profiles versus time on days 1 and 4. The pharmacokinetics was best described by a 2-compartment model with a link to bronchial secretions. The population pharmacokinetic parameters were as follows (given as estimate with percent interindividual variability in parentheses except where otherwise indicated): clearance, 14.3 L/h (25%); central distribution volume, 62.9 L (14%); intercompartmental clearance, 27.2 L/h (36%); peripheral distribution volume; 71 L (32%); fraction of moxifloxacin clearance to bronchial secretions, 0.11 (range, 0.06-0.16); and elimination rate constant for bronchial secretions, 1.7 h(-1) (40%). The plasma terminal half-life was 6.7 hours. The bronchial-to-plasma exposure ratio was 1.0 (range, 0.6-2.0). With a conservative 90% minimum inhibitory concentration (MIC90) of 0.25 mg/L, the maximum concentration/MIC90 ratios were higher than 10 and the area under the curve/MIC90 ratios were roughly 100 for plasma and bronchial secretions. Conclusions: This study showed the fast diffusion of moxifloxacin into the lungs in ventilated patients with severe respiratory infection. The bronchial secretions reached bactericidal levels for common germs found in respiratory tract infections.