Therapeutic Drug Monitoring for Linezolid in the Treatment of Rifampin-resistant Tuberculosis

Who May Qualify: - Adult male or female patient \> 18 years of age - Microbiological confirmation of rifampicin-resistant tuberculosis (e.g., phenotypic drug susceptibility testing, GeneXpert MTB/RIF™). Participants may have resistance to additional medications as well - i.e., MDR and XDR TB - but must have resistance to at least rifampin - Initiated on a RR-TB treatment regimen containing linezolid, no more than 14 days prior to enrollment - HIV status is known - Both HIV-positive and HIV-negative individuals are eligible - If an individual reports unknown HIV results, they must consent to HIV testing at time of enrollment to confirm status. If they decline to be tested, they are not eligible for the study - If an individual declines to share his or her HIV status, they are not eligible for the study. Patients reporting unknown HIV status will be required to have had confirmatory testing within 6 months of study screening Who Should NOT Join This Trial: - Current unstable or uncontrolled major medical comorbidity that would interfere with subject's ability to participate in the study - Pregnant at time of screening - Initial linezolid dose \< 600mg daily Always talk to your doctor about whether this trial is right for you.