Shortening the duration of treatment for patients with drug sensitive tuberculosis from 6 to 4 months has been attempted many times in clinical trials but thus far all have failed. These failures reveal our incomplete understanding of factors driving the need for such extensive treatments. Consistently, trials have demonstrated that 80-85% of patients are successfully cured after 4 months of therapy, including the extensive set of studies from the British Medical Research Council (BMRC) in the 1970s and 1980, the Tuberculosis Research Unit (TBRU) treatment shortening study in non-cavitary patients who achieve early culture conversion, and the more recent treatment shortening trials using fluoroquinolones like REMoxTB. The current standard of care is to over-treat all patients for a total of 6-months to avoid relapse in a small subset of patients at higher risk for incompletely understood reasons.
For decades, clinical investigators have attempted to establish culture conversion as a predictor of treatment success. Despite the appealing logic, the real correlation of culture conversion as a surrogate endpoint has been consistently disappointing. In the REMoxTB trial, in particular, the intensive microbiological data collected revealed unambiguously that clearance of bacteria from the sputum did not sufficiently correlate with relapse risk to be a useful surrogate for durable cure. An important subset of patients, despite clearing their sputum of TB quickly and complying with all of their medications, still remained at high risk of relapsing with active disease after stopping treatment. Likewise there are patients who clear their sputum of bacteria slowly that nonetheless go on to achieve durable cure. Intuitively this makes sense: only those bacteria at the surface of a cavity are directly open to the airways to seed the sputum. Yet this is not the full story as there are also heterogeneous lesions within each individual patient which respond differently to treatment with chemotherapy.
This protocol builds upon the historical trials and several successful small studies that suggest that directly monitoring lung pathology using (18F)- FDG PET/CT correlates better with treatment outcome than culture status. We will prospectively identify patients at low risk based on their baseline radiographic extent of disease, and further refine this risk score by evaluating the rate of resolution of the lung pathology (CT) and inflammation (PET) at one month as well as checking an end-of-treatment GeneXpert test for the sustained presence of bacteria. Patients classified as low risk will be randomized to receive a shortened 4- month or a full 6-month course of therapy. If successful, this trial will both offer a badly needed alternative to culture status as a trial-level surrogate marker for outcome as well as provide critical information for preclinical and early clinical efforts to identify new agents and combinations with the potential to shorten therapy.
Hypothesis: A combination of radiographic characteristics at baseline, the rate of change of these features at one month, and markers of residual bacterial load at the end of treatment will identify patients with tuberculosis who are cured with 4 months (16 weeks) of standard treatment.
