Bactericidal drugs in ATT are:

Pyrazinamide (Z): Chemically similar to INH.It is weakly tuberculocidal but more active in acidic medium. It is more lethal to intracellularly located bacilli and to those at sites showing an inflammatory response (pH is acidic at both these locations).By killing the residual intracellular bacilli it has good &;sterilizing&; activity. Its use has enabled regimens to be shoened and risk of relapse to be reduced. Mechanism of antimycobacterial action of Z resembles INH; it inhibits mycolic acid synthesis, but by interacting with a different fatty acid synthase encoding gene. Ethambutol (E): Ethambutol is selectively tuberculostatic and clinically as active as S. PAS is tuberculostatic and one of the least active drugs: does not add to the efficacy of more active drugs that are given with it; only delays development of resistanceprobably, by directly inhibiting episomal resistance transfer. Resistance to PAS is slow to develop. It is used as the sodium salt (large doses that are needed may cause Na+ overload) or calcium salt (better gastric tolerance is claimed) ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:742,743