Preserved efficacy and reduced toxicity with intermittent linezolid dosing in combination with bedaquiline and pretomanid in a murine TB model

The novel regimen of bedaquiline, pretomanid, and linezolid (BPaL) is highly effective against drug resistant tuberculosis, but linezolid toxicities are frequent. We hypothesized that, for a similar total weekly cumulative dose, thrice-weekly administration of linezolid would preserve efficacy while reducing toxicity compared to daily dosing, in the context of the BPaL regimen. Using C3HeB/FeJ and BALB/c mouse models of tuberculosis disease, thrice-weekly linezolid dosing was compared to daily dosing, with intermittent dosing introduced (a) from treatment initiation or (b) following an initial period of daily dosing. In all animals, BPa was dosed daily throughout treatment. Blood counts were used to assess hematologic toxicity. Following unexpected findings of apparent antagonism, we conducted additional experiments to investigate strain-to-strain differences in the contribution of linezolid to regimen efficacy comparing each 1- and 2-drug component to the BPaL regimen in BALB/c mice infected with Mycobacterium tuberculosis H37Rv or HN878. Giving linezolid daily for 1-2 months achieved the greatest efficacy, but following that, results were similar if the drug was stopped, dosed thrice-weekly, or continued daily. Erythrocyte counts were lower with daily than thrice-weekly dosing. Linezolid had additive effects with BPa against M. tuberculosis H37Rv but antagonistic effects with BPa against M. tuberculosis HN878. However, overall efficacy of BPaL was high and similar against both strains. Dosing linezolid daily for the first two months, then less frequently thereafter, may optimize its therapeutic margin. Linezolids contribution to BPaL regimens may depend on M. tuberculosis strain.