- Has initiated an appropriate optimized background regimen (OBR) MDR-TB treatment regimen as per routine treatment decision, at least two weeks but not more than eight weeks prior to enrollment, and in the opinion of the site investigator, is tolerating the regimen well at enrollment. Note: An appropriate OBR MDR-TB treatment regimen is defined as including components based on the sensitivities of the infecting isolate, if known, and past treatment history, if known. This regimen should also follow the OBR MBR-TB treatment guidelines as described in the protocol.