<p><strong>Rifampicin:</strong>&nbsp;It is a semisynthetic derivative of rifamycin, suppresses bacterial RNA synthesis by binding to the &beta;-subunit of DNA-dependent RNA polymerase, thus inhibiting the attachment of the enzyme to DNA, blocking RNA transcription and elongation. It does not inhibit the counterpart mammalian enzyme.<br />
Rifampicin has a bactericidal action and a potent sterilizing effect against both intracellular and extracellular tubercle bacilli. Cross-resistance has been shown only with other rifamycin derivatives.<br />
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<strong>Isoniazid:</strong>&nbsp;It kills actively growing tubercle bacilli by inhibiting the biosynthesis of mycolic acids, which are the major components of the bacterial cell wall of Mycobacterium tuberculosis.<br />
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<strong>Pyrazinamide:</strong>&nbsp;Pyrazinamide, an antituberculous drug, is the pyrazine analog of nicotinamide. The precise mechanism of action of pyrazinamide is not known. Its metabolite, pyrazinoic acid, which is less active in vitro may possibly be involved in the in vivo activity of pyrazinamide.<br />
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<strong>Ethambutol:</strong>&nbsp;Ethambutol diffuses slowly into actively growing Mycobacteria cells eg, tubercle bacilli. It inhibits the synthesis of 1 or more metabolites, thus causing impaired cell metabolism, arrest cell multiplication and induce cell death. No cross-resistance with other agents has been demonstrated.<br />
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<strong>Spectrum of Activity:</strong>&nbsp;Rifampicin, isoniazid, pyrazinamide, and ethambutol, at therapeutic levels, have demonstrated bactericidal activity against both intracellular and extracellular Mycobacterium tuberculosis organism.</p>