The repurposed agent moxifloxacin has become an important addition to the physician’s armamentarium for the therapy of Mycobacterium tuberculosis . When a drug is administered, we need to have metrics for success. As for most antimicrobial chemotherapy, we contend that for Mycobacterium tuberculosis therapy, these metrics should be a decline in the susceptible bacterial burden and the suppression of amplification of less-susceptible populations.