<i>In vitro</i> antimicrobial resistance properties of rifapentine and rifampicin are indistinguishable

ABSTRACT Tuberculosis (TB) is a major global health threat, with millions of new cases diagnosed annually. Rifampicin is a cornerstone drug in the current standard of care for TB treatment. Recently, rifapentine, an analog of rifampicin, has been considered as an alternative to rifampicin primarily due to its longer half-life and shorter 4-month TB treatment regimens. Despite some encouraging advantages in the clinical setting, the rifamycin resistance mutation frequency and type have yet to be systematically investigated. The mutation identity and frequency could directly impact clinical outcomes and the epidemiology of TB resistance. Our objective was to compare the in vitro antimicrobial properties of rifapentine and rifampicin across four Mycobacterium tuberculosis strains, namely H37Rv, CDC1551, HN878, and W4, a lineage 2 (Beijing) genotype, and to determine whether resistance differed between the two drugs. We compared the frequency of resistance between rifampicin and rifapentine at various concentrations, and evaluated the frequency of different mutation types in the four chosen TB strains via Sanger sequencing. Overall, no significant differences were observed in the frequency of resistance or mutation identity between rifampicin and rifapentine; however, strain-dependent differences were noted. H37Rv showed a higher frequency of resistance at all concentrations tested in both drugs compared to CDC1551 and the Beijing strains W4 and HN878. The profound overlap in in vitro properties between the two antimicrobials provides valuable insight for the ongoing evaluation of rifapentine as a viable alternative to rifampicin in the standard of care for TB treatment. IMPORTANCE Recent clinical trials demonstrate that a 4-month regimen combining rifapentine, isoniazid, pyrazinamide, and moxifloxacin is non-inferior to the standard 6-month rifampicin-based regimen. This shorter regimen, with less frequent rifamycin administration, may enhance patient compliance and treatment outcomes. However, two pivotal questions warrant attention before proceeding with a switch to rifapentine-based treatments. First, we must ensure that rifapentine maintains comparable or lower rates of rifamycin resistance, as an increased rate of resistance mutations would undermine the new regimen’s viability. Second, we need to confirm whether current molecular diagnostic tools can accurately detect rifapentine resistance with equivalent sensitivity and specificity. Thus, any rifapentine-specific mutations and their frequency must be identified and incorporated into existing molecular diagnostic platforms if novel. In our investigation, we found that the mutation frequency and repertoire were not significantly different between rifampicin and rifapentine within strains. Current diagnostic methods should be equally sensitive to rifapentine and rifampicin resistance.