**3. Revisiting Established Targets: Revisiting Targets Proven as Druggable by Using Broad-Spectrum Compounds**

TB was declared a global emergency by WHO in 1996 [24]. The emergence of drug-resistant TB and the complete lack of drugs capable of treating patients with MDR TB led the drug development community to investigate alternate approaches to rapidly induct novel drugs into the regimen. This prompted investigations into the feasibility of introducing the existing broad-spectrum antibacterial drugs into the TB treatment regimen. Several antibacterial classes that have been shown to be active on MTB in vitro were investigated in clinical trials.

This approach, which is now classified as 'repurposing', has successfully delivered new options for TB treatment. The key classes that have added to the anti-TB portfolio are the following:
