Name two newer TB drugs used for MDR/XDR-TB with distinct mechanisms.

• A. Isoniazid and Rifampin.
• B. Ethambutol and Pyrazinamide.
• C. Streptomycin and Amikacin.
• D. Bedaquiline (ATP synthase inhibitor) and Delamanid (inhibits mycolic acid synthesis and generates reactive nitrogen species).

Answer: (D)

The idea is to recognize two new TB drugs used specifically for MDR/XDR-TB that work in different ways. Bedaquiline disrupts energy production by inhibiting the bacterial ATP synthase, effectively starving Mycobacterium tuberculosis of the energy it needs to survive. Delamanid, on the other hand, blocks the synthesis of mycolic acids, a key component of the bacterial cell wall, and it also generates reactive nitrogen species that damage the bacteria. Using drugs with distinct mechanisms helps overcome resistance and strengthens regimens for MDR/XDR-TB.

The other options point to older drugs that are not both newer therapies with distinct mechanisms. Isoniazid, rifampin, ethambutol, pyrazinamide, streptomycin, and amikacin are established agents with shared histories in TB treatment, and they do not pair two newer agents with different targets the way bedaquiline and delamanid do. Note that both bedaquiline and delamanid require monitoring for effects like QT prolongation, but their different modes of action make them a compelling combination for MDR/XDR-TB.