Pharmacokinetic model of levofloxacin in plasma, lung tissue and bronchial mucosa. Xa, X1, X2 and X3 denote the amount of levofloxacin in absorption, central, lung and bronchial compartment, respectively. ka represents the absorption rate of levofloxacin. CL is the clearance of levofloxacin. V1, V2, and V3 indicate the distribution volume in the central, lung, and bronchial compartment. f12 and f13 indicate the fraction of levofloxacin clearance from central to the lung and bronchial compartment, respectively. CL2 and CL3 are the clearance of levofloxacin from the lung and bronchial compartment, respectively.