Several nitrogen-containing fused heterocycles play an important role in the anti-TB Medicinal Chemistry. Shirude and coworkers  from AstraZeneca® (AstraZeneca R&D, Bangalore, India) have reported a promising 1,4-azaindole derivative identified after an optimization process . Compound (12) (Figure 4) was characterized as a potent derivative against MDR-TB, with MIC90 values ranging from 0.78 to 1.56 μM with low cytotoxicity against human leukemia monocytic (THP-1) cells (IC50 > 100 μM). In vivo studies were performed with compound (12) in order to determine its efficacy and pharmacokinetics profile. In rats, this molecule was able to reduce the bacterial burden on a logarithmic scale of 1 log10 colony forming units (CFUs)/lung at 300mg kg−1 of body weight, and statistically significant dose-dependentefficacy was observed. On the other hand, pharmacokinetic analysis revealed low clearance rates, excellent bioavailability and no interference with any of the cytochrome P450 (CYP450) isoenzymes. Nevertheless, this compound presented a rapid metabolism in the presence of mouse liver microsomes . Unsuccessful attempts to optimize this compound have identified compound (13) as active against INH-resistant strains; however, with MIC90 value of 14.3 μM . Danac and Mangalagiu have reported the synthesis and antituberculosis activity of a series of fused bipyridine heterocycles. Compound (14) (Figure 4) presented promising activity against several single resistant Mtb strains, with MIC90 values ranging from 3.3–9.2 μM .