4.3 Algorithm 3 – DST for second-line drugs for people with RR-TB or MDR-TB

Algorithm 3 is used for further evaluation of people with RR-TB or MDR-TB. In its most recent recommendations (9), WHO stresses the importance of DST before starting the preferred all-oral BDQ-containing MDR-TB regimen, especially for medicines for which mWRDs are available. Two of the key medicines in these regimens are BDQ and FQ. Currently, the only WHO-recommended molecular test to detect mutations associated with BDQ resistance is a targeted NGS test (Deeplex® Myc-TB from GenoScreen). Algorithm 3a relies on testing using the targeted NGS test to detect mutations associated with resistance to BDQ, FQ, LZD and other medicines used in the recommended regimens. Because of the limited availability of targeted NGS tests at this time, a second algorithm (Algorithm 3b) is included that relies on the detection of mutations associated with FQ resistance using WHO-recommended molecular tests (a low complexity automated NAAT and SL-LPA). In addition to molecular testing, WHO stresses the need to scale up laboratory phenotypic DST capacity for medicines for which there are accurate and reproducible phenotypic methods, including BDQ, LZD, Pa, CS, CFZ and DLM. As in any potentially life-saving situation, treatment for DR-TB should not be withheld from a person because of a lack of complete DST results.

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