Response to treatment should be monitored on the basis of monthly sputum smear microscopy and culture (ideally at the same frequency). Individuals prescribed the BPaLM/BPaL regimen should be monitored to assess regimen effectiveness and safety. Given that the BPaLM/BPaL regimen is a new and shorter regimen that includes novel medications, it is also important to follow up patients after the completion of treatment, to ensure that there is no treatment relapse or unexpected adverse events.
The treatment outcome definitions and reporting framework for patients on the BPaLM/BPaL regimen are the same as those for patients on longer MDR-TB regimens (38). The updated definition of treatment failure includes situations where a patient’s treatment regimen has been terminated or permanently changed to a new treatment regimen, due to any of the following:
- Adverse drug reactions – If bedaquiline or pretomanid need to be suspended permanently owing to severe toxicity, the entire regimen will need to be terminated and a longer individualized treatment regimen considered. Should moxifloxacin alone need to be suspended in the BPaLM regimen, the regimen can be continued as the BPaL regimen. If linezolid alone needs be suspended when the remaining time to complete the regimen is less than 8 weeks, the treatment should be completed with the remaining drugs in the regimen.
- Poor bacteriological or clinical response to treatment – If there is bacteriological evidence of persistent positive cultures or poor clinical response, a change in the treatment regimen should be considered. Bacteriological failure for BPaLM/BPaL is marked by persistent positive sputum culture (no conversion or reversion) from month 4 to the end of treatment (after 6 months for BPaLM and after 9 months for BPaL). Where an individual fails to respond to the BPaLM/BPaL regimen, the patient should be transferred to a longer individualized regimen (Chapter 6) and provided with adequate treatment support. In such patients, DST, where available, is important to guide the design of the next regimen.
- Acquired drug resistance to drugs in the BPaLM/BPaL regimen – If resistance to BPaLM/BPaL component drugs (except moxifloxacin) is acquired during treatment (i.e. baseline DST is susceptible and monitoring culture demonstrates resistance), it will be necessary to discontinue the regimen.
Finally, there is growing evidence of both bedaquiline and linezolid resistance being expressed in M. tuberculosis strains, especially for those who have been exposed to either medication previously (39, 40). The capacity to monitor for the emergence of resistance with DST will be instrumental in controlling, treating and preventing the emergence and spread of resistant strains of infection.