In Vivo Pharmacokinetic and Pharmacodynamic Profiles of Antofloxacin against Klebsiella pneumoniae in a Neutropenic Murine Lung Infection Model

Abstract

Antofloxacin is a novel broad-spectrum fluoroquinolone under development for the treatment of infections caused by a diverse group of bacterial species. We explored the pharmacodynamic (PD) profile and targets of antofloxacin against seven Klebsiella pneumoniae isolates by using a neutropenic murine lung infection model. Plasma and bronchopulmonary pharmacokinetic (PK) studies were conducted at single subcutaneous doses of 2.5, 10, 40, and 160 mg/kg of body weight. Mice were infected intratracheally with K. pneumoniae and treated using 2-fold-increasing total doses of antofloxacin ranging from 2.5 to 160 mg/kg/24 h administered in 1, 2, 3, or 4 doses. The E_max Hill equation was used to model the dose-response data. Antofloxacin could penetrate the lung epithelial lining fluid (ELF) with pharmacokinetics similar to those in plasma with linear elimination half-lives over the dose range. All study strains showed a 3-log₁₀ or greater reduction in bacterial burden and prolonged postantibiotic effects (PAEs) ranging from 3.2 to 5.3 h. Dose fractionation response curves were steep, and the free-drug area under the concentration-time curve over 24 h (AUC_0-24)/MIC ratio was the PD index most closely linked to efficacy (R² = 0.96). The mean free-drug AUC_0-24/MIC ratios required to achieve net bacterial stasis, a 1-log₁₀ kill, and a 2-log₁₀ kill for each isolate were 52.6, 89.9, and 164.9, respectively. When integrated with human PK data, these PD targets could provide a framework for further optimization of dosing regimens. This could make antofloxacin an attractive option for the treatment of respiratory tract infections involving K. pneumoniae.

Keywords: Klebsiella pneumoniae; PK/PD; antofloxacin; murine lung infection.

FIG 1

(A and B) Pharmacokinetic profiles of antofloxacin in plasma (A) and pulmonary ELF (B) after subcutaneous administration of single doses of 2.5, 10, 40, and 160 mg/kg in lung-infected neutropenic mice. (C and D) Data corresponding to panels A and B plotted on semilogarithmic coordinates. Filled and open symbols represent concentrations in plasma and ELF, respectively. Each symbol represents the mean ± standard deviation of the levels in the plasma or ELF of six mice.

FIG 2

In vivo postantibiotic effect estimates after a single subcutaneous dose of antofloxacin using a neutropenic mouse lung model. Each symbol represents the mean and standard deviation of data from four lungs infected with K. pneumoniae ATCC 35657. The black horizontal bars represent the time that plasma antofloxacin concentrations remained above the MIC for the infecting organism.

FIG 3

In vivo dose fractionation with antofloxacin using the murine neutropenic lung infection model. Each symbol represents the mean of data from four lungs infected with K. pneumoniae ATCC 35657. Seven total antofloxacin dose levels (mg/kg/24 h) were fractionated into each of four dose regimens. The microbial burden was measured at the start and after 24 h of therapy.

FIG 4

Impact of pharmacodynamic regression in the in vivo dose fractionation study with antofloxacin against K. pneumoniae ATCC 35657. Each symbol represents the mean of data from four thighs. The dose data are expressed as the free-drug AUC/MIC (A), the percentage of time that drug levels are above the MIC (%fT>MIC) (B), and C_max/MIC (C). The R² values are the coefficients of determination. The EC₅₀ represents the PK/PD index associated with 50% of the maximal effect (E_max), and N is the Hill coefficient. The line drawn through the data points is the best-fitting line based upon the sigmoid E_max model.

FIG 5

In vivo dose effect of antofloxacin against seven selected K. pneumoniae isolates using the murine neutropenic lung infection model. Each symbol represents the mean of data from four thighs. Seven total antofloxacin dose levels were divided into a regimen of administration every 12 h. Microbial burdens were measured at the start and after 24 h of therapy. The horizontal dashed line at 0 represents the burden of organisms in the lungs of mice at the start of therapy. Data points below the line represent killing, and points above the line represent growth.