fThe antileprosy drug clofazimine has shown potential for shortening tuberculosis treatment; however, the current dosing of the drug is not evidence based, and the optimal dosing is unknown. Our objective was to conduct a preclinical evaluation of the pharmacokinetics and pharmacodynamics of clofazimine in the mouse model of tuberculosis, with the goal of providing useful information on dosing for future studies. Pharmacokinetic parameters were evaluated in infected and uninfected BALB/c mice. Pharmacodynamic parameters were evaluated in Mycobacterium tuberculosis-infected mice that were treated for 12 weeks with one of six different clofazimine dosing regimens, i.e., doses of 6.25, 12.5, and 25 mg/kg of body weight/day and 3 regimens with loading doses. Clofazimine progressively accumulated in the lungs, livers, and spleens of the mice, reaching levels of greater than 50 g/g in all tissues by 4 weeks of administration, while serum drug levels remained low at 1 to 2 g/ml. Elimination of clofazimine was extremely slow, and the half-life was dependent on the duration of drug administration. Clofazimine exhibited dosedependent tissue and serum concentrations. At any dose, clofazimine did not have bactericidal activity during the first 2 weeks of administration but subsequently demonstrated potent, dose-independent bactericidal activity. The antituberculosis activity of clofazimine was dependent on neither the dose administered nor the drug concentrations in the tissues, suggesting that much lower doses could be effectively used for tuberculosis treatment. C lofazimine (CFZ) is a phenazine dye developed in the 1950s for the treatment of tuberculosis (TB) (1, 2). Despite promising activity against Mycobacterium tuberculosis both in vitro and in vivo, clofazimine was not advanced as a TB drug but instead became incorporated decades later into the multidrug treatment of leprosy, where it remains a key drug (3, 4). Interest in clofazimine for TB treatment has been revitalized following the 2010 report by Van Deun and colleagues that a clofazimine-containing regimen not only was highly effective for the treatment of multidrug-resistant (MDR) TB, but was also associated with a significantly decreased duration of therapy (5); 9 months of a clofazimine-containing regimen resulted in 87.9% relapse-free cure, which is in sharp contrast to the limited efficacy (less than 50% relapse-free cure) of the World Health Organization (WHO)-recommended, at least 20-month-long MDR-TB treatment regimen (6, 7). This report was complemented by experimental chemotherapy studies in which the inclusion of clofazimine in first-and secondline regimens significantly shortened the duration of treatment needed for relapse-free cure in mouse models of drug-susceptible and MDR TB, respectively (8, 9). These clinical and preclinical data suggest that clofazimine has great potential for TB treatment.Because clofazimine was abandoned as an option for TB treatment shortly after its discovery, and also because the use of clofazimine for leprosy is not ba...