Moxifloxacin, ofloxacin, sparfloxacin, and ciprofloxacin against Mycobacterium tuberculosis: evaluation of in vitro and pharmacodynamic indices that best predict in vivo efficacy

Abstract

Members of the fluoroquinolone class are being actively evaluated for inclusion in tuberculosis chemotherapy regimens, and we sought to determine the best in vitro and pharmacodynamic predictors of in vivo efficacy in mice. MICs for Mycobacterium tuberculosis H37Rv were 0.1 mg/liter (sparfloxacin [SPX]) and 0.5 mg/liter (moxifloxacin [MXF], ciprofloxacin [CIP], and ofloxacin [OFX]). The unbound fraction in the presence of murine serum was concentration dependent for MXF, OFX, SPX, and CIP. In vitro time-kill studies revealed a time-dependent effect, with the CFU reduction on day 7 similar for all four drugs. However, with a J774A.1 murine macrophage tuberculosis infection model, CIP was ineffective at up to 32x MIC. In addition, MXF, OFX, and SPX exhibited less activity than had been seen in the in vitro time-kill study. After demonstrating that the area under the concentration-time curve (AUC) and maximum concentration of drug in plasma were proportional to the dose in vivo, dose fractionation studies with total oral doses of 37.5 to 19,200 mg/kg of body weight (MXF), 225 to 115,200 mg/kg (OFX), 30 to 50,000 mg/kg (SPX), and 38 to 100,000 mg/kg (CIP) were performed with a murine aerosol infection model. MXF was the most efficacious agent (3.0+/-0.2 log10 CFU/lung reduction), followed by SPX (1.4+/-0.1) and OFX (1.5+/-0.1). CIP showed no effect. The ratio of the AUC to the MIC was the pharmacodynamic parameter that best described the in vivo efficacy. In summary, a lack of intracellular killing predicted the lack of in vivo activity of CIP. The in vivo rank order for maximal efficacy of the three active fluoroquinolones was not clearly predicted by the in vitro assays, however.

FIG. 1.

Percentage of free drug as a function of the total concentration. ▪, MXF; □, OFX; •, SPX; ○, CIP.

FIG. 2.

Effects of increasing fC/MIC ratios on the bactericidal activities of MXF (panel A), OFX (B), SPX (C), and CIP (D) on days 1, 7, and 14 after the addition of drug. Each point represents the mean of triplicate values. The bactericidal effect is calculated on the basis of the initial inoculum prior to the addition of the drug.

FIG. 3.

Effects of increasing fC/MIC ratios on the intracellular bactericidal activities of the four fluoroquinolones, MXF, OFX, SPX, and CIP, against M. tuberculosis in the J774A.1 murine macrophage cell line after 3 days of exposure to the drug. Each point represents the mean ± standard deviation of triplicate values. The bactericidal effect is calculated on the basis of the initial inoculum prior to addition of the drug.

FIG. 4.

Dose proportionality and limits of linearity for the four fluoroquinolones with respect to fC_max/MIC (A), fAUC/MIC (B), and fT_>MIC (percent) (C).

FIG. 5.

Relationship between fAUC/MIC, fC_max/MIC, and fT_>MIC (percent) of the four fluoroquinolones and log₁₀ CFU/lung of M. tuberculosis when the total dose is fractionated as per the design shown in Table 3. Each point represents the mean ± standard deviation of triplicate values.