This study investigated the potential of developing long-acting injectable (LAI) formulations of the next-generation diarylquinoline antibacterial compounds TBAJ-587 and TBAJ-876, which have the potential to impact the tuberculosis (TB) treatment by providing an extended treatment option. The performance of these compounds, formulated as LAIs, were evaluated based on particle size stability, drug loading capacity, and in vivo pharmacokinetics in rats. The data showed that particularly high drug loadings could be obtained in aqueous suspensions using the salt forms of TBAJ-587 and TBAJ-876, with concentrations up to 750 mg/mL TBAJ-587 fumarate and 650 mg/mL TBAJ-876 tartrate, expressed as the equivalent concentration of free base. A long-term stability study of the TBAJ-876 tartrate formulation suggested that a relatively stable suspension was defined when stored at both ambient temperature and at 40 °C. In contrast, the TBAJ-587 fumarate suspension formulation showed significant particle size growth as a function of time, indicating physical instability in the colloidal system. Analysis of both compounds by X-ray powder diffraction (XRPD) revealed no major changes in the crystal structure following milling or after 24 weeks of storage at 40 °C. The in vivo pharmacokinetic study in rats showed that the suspensions containing either TBAJ-587 fumarate or TBAJ-876 tartrate offered a promising LAI option for the prolonged treatment of TB, as all formulations achieved prolonged drug plasma exposure for at least three months following administration.

Control of Mycobacterium tuberculosis infection continues to be an issue, particularly in countries with a high tuberculosis (TB) burden in the tropical and sub-tropical regions. The effort to reduce the catastrophic cost of TB with the WHO's End TB Strategy in 2035 is still obstructed by the emergence of drug-resistant TB (DR-TB) cases as result of various mutations of the MTB strain. In the approach to combat DR-TB, several potential antitubercular agents were discovered as inhibitors for various existing and novel targets. Host-directed therapy and immunotherapy also gained attention as the drug-susceptibility level of the pathogen can be reduced due to the pathogen's evolutionary dynamics. This review is focused on the current progress and challenges in DR-TB treatment. We briefly summarized antitubercular compounds that are under development and trials for both DR-TB drug candidates and host-directed therapy. We also highlighted several problems in DR-TB diagnosis, the treatment regimen, and drug discovery that have an impact on treatment adherence and treatment failure.