As detailed previously, DST for fluoroquinolones is advisable before starting therapy. Where DST is unavailable, a careful history of previous exposure to TB therapy is critical. Where the treatment history suggests there may be resistance to one of the components of the regimen (i.e. exposure to bedaquiline, pretomanid or linezolid in an inadequate regimen is greater than 1 month and DST is unavailable), the BPaLM/BPaL therapy should not be commenced, and a longer individualized regimen should be considered. Furthermore, if there is greater than 1 month exposure to fluoroquinolones that indicates probable resistance, the BPaLM regimen should be continued until resistance to fluoroquinolones is determined.
Previous exposure to delamanid may suggest cross-resistance to pretomanid (31) and exposure to clofazimine may suggest cross-resistance to bedaquiline (32). Caution should be exerted in such situations and, where possible, if DST for clofazimine, bedaquiline or delamanid is available, it should be used.