FIG. 5.

Comparison of levels of antimycobacterial effectiveness of free rifampin versus equivalent doses delivered with rifampin-loaded microspheres. Three experiments were performed, i.e., experiments 1 (A), 2 (B), and 3 (C). J774 macrophages were infected with M. tuberculosis H37Rv and treated with no rifampin (○), 0.09 ± 0.002 μg of rifampin/well (n = 9) (■) as free drug, or 0.097 ± 0.008 μg of rifampin/well (n = 9) delivered in microsphere formulation no. 5 (□). Numbers of CFU were determined in triplicate at 0 and 7 days, as described in Materials and Methods. In each experiment, the difference between the mean value for the nontreated control and that for drug-treated sets was significant at P ≤ 0.001. Also, in each experiment the difference between the mean values for the cells treated with free rifampin versus those treated with rifampin-loaded microspheres was significant at P ≤ 0.001. Significance was determined by one-way analysis of variance, and a correction for multiple comparisons (posttest) was performed by the Tukey-Kramer multiple-comparisons test.