Fluoroquinolone Efficacy against Tuberculosis Is Driven by Penetration into Lesions and Activity against Resident Bacterial Populations

Lesion-centric pharmacokinetic-pharmacodynamic (PK/PD) parameters of the fluoroquinolones calculated using potency measured against intracellular M. tuberculosis in primary macrophages and extracellular M. tuberculosis in rabbit caseum. (A) Activated macrophages were infected with M. tuberculosis and treated with the fluoroquinolones for 3 days as indicated. Relative growth or survival rates on day 3 compared to pretreatment are shown (means ± standard deviation [SD], n = 3). (B) Bactericidal activity of the fluoroquinolones against ex vivo M. tuberculosis in cavity caseum, where tuberculous bacilli are rich in lipid inclusions and exhibit phenotypic drug resistance (45). Data are expressed as CFU per milliliter of homogenized caseum (diluted 1:3 in water), plotted on a log scale (means ± SD, n = 3). LOD, limit of detection. (C) Lesion-specific PK/PD parameters calculated as the ratios between the drugs’ area under the curve in cellular lesions (AUC_cellular) or caseum (AUC_caseum) and the drugs’ inhibitory or cidal activity against the corresponding intracellular and extracellular M. tuberculosis bacilli. MacIC₉₀, concentration that inhibits 90% of growth in macrophages; MacMBC₉₀, concentration that kills 90% of M. tuberculosis bacilli in macrophages (A); WCC₉₀, Wayne cidal concentration or concentration that kills 90% of extracellular M. tuberculosis under anaerobic conditions (47); casMBC₉₀, concentration that kills 90% of M. tuberculosis bacilli in ex vivo rabbit caseum (45) (B). Means ± SD of data from 100 simulated granulomas or caseous foci are shown.

(A) Steady-state AUC_[0–24] distributions in plasma, uninvolved lung, cellular lesions, and caseum of rabbits receiving human-equivalent doses of MXF, LVX, and GTX as indicated. The PK variability was introduced by sampling 100 plasma PK parameter sets from the distributions given in Table S1. (B) Probability of target attainment for a PK/PD target AUC_[0–24]/MIC of 125 to achieve 90% of maximal kill (15, 18, 19). The gray areas indicate the range of MIC as reported by Angeby et al. (48). Red, orange, olive, and green lines indicate the probability of target attainment in plasma, uninvolved lung, cellular lesions, and caseum, respectively. The minimum concentration required to achieve 90% growth inhibition of intracellular M. tuberculosis (MacIC₉₀) and the concentration required to kill 90% of nonreplicating M. tuberculosis bacilli in caseum (casMBC) are indicated by arrows. These two potency values were determined using M. tuberculosis strains H37Rv and HN878; thus, the impact of potency variability on target attainment and efficacy predictions is unknown.

Comparative efficacies of the three fluoroquinolones in the rabbit model of active TB. (A) Effect of MXF (blue), GTX (purple), and LVX (orange) daily treatment at human-equivalent doses on bacterial burden in uninvolved lung, cellular lesions and necrotic lesions, compared to vehicle-treated controls (gray), at 4 and 8 weeks of treatment. Data are presented as median ± 95% confidence interval; n = 4 to 6 rabbits or 13 to 59 lesions per lesion category and treatment group, with data determined using the two-tailed Mann-Whitney U (nonparametric) test. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; ns, not significant. (B) Effect of MXF (blue), GTX (purple), and LVX (orange) treatment on sterilization of lung tissue and lesions, shown as proportions of sterile uninvolved lung samples and lesions. Actual ratios are shown above each bar. Sample size and P value categories correspond to those described for panel A. Fisher's exact test (two-sided) was performed for comparisons of treated versus untreated group pairs. (C) Effect of fluoroquinolone treatment on lesion weight. Sample size and statistical analysis correspond to those described for panel A. (D) Effect of MXF (blue), GTX (purple), and LVX (orange) treatment on bacterial kill in lung and lesions, calculated as the ratio between CEQ (chromosome equivalents; cumulative burden) and CFU (actual live burden at the time of sampling). Data points with undetectable CEQ were removed from the analysis since the CEQ LOD is approximately 100 (33) and the CFU LOD is 3 to 5. n = 4 to 6 rabbits or 7 to 54 lesions per lesion category and treatment group (2/4 MXF-treated rabbits had few lesions left after 2 months of treatment, hence the reduced number of lesions in this group), with data determined using the two-tailed Mann-Whitney U (nonparametric) test. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; ns, not significant.