In vitro and in vivo activity of omadacycline against Mycobacterium tuberculosis

The bedaquiline (B), pretomanid (Pa), and linezolid (L) (BPaL) regimen is highly effective for drug-resistant tuberculosis (TB) but is limited by linezolid-associated toxicities, including myelosuppression and peripheral neuropathy. We evaluated omadacycline as a representative tetracycline-class protein synthesis inhibitor (PSI) to assess whether it can contribute functional activity within a BPa backbone. Omadacycline exhibited a minimum inhibitory concentration (MIC) of 2-4 μg/mL against M. tuberculosis H37Rv and 10-48 μg/mL against representatives of four global clades. Daily media replacement reduced the MIC against H37Rv to 0.29 μg/mL, suggesting antibiotic instability may underestimate in vitro potency. In vivo, subcutaneous administration of omadacycline (15 mg/kg) in BALB/c mice, yielding plasma exposures within the range of those reported for the approved 300-mg oral human dose, led to a 0.7-log₁₀ reduction in lung colony-forming units (CFU) in both acute and chronic TB models. In combination therapy, 10-week treatment with BPa plus either linezolid (BPaL) or omadacycline (BPaO) further reduced lung CFU by ∼1 log₁₀ relative to BPa alone, demonstrating the contribution of a PSI to regimen efficacy. Notably, BPaO and BPaL reduced relapse rates after 10 weeks of treatment to 43 and 23%, respectively, compared to 100% relapse in the BPa-only group. Together, these findings provide proof-of-concept evidence that omadacycline has in vivo antitubercular activity, achieves clinically relevant exposures, and can contribute functional PSI activity in combination regimens however, these results do not establish clinical equivalence with linezolid and support further evaluation of tetracycline-class agents in TB therapy.