Ciprofloxacin (prototype): It is the most potent first generation FQ acti*e against a broad range of bacteria, the most susceptible ones are the aerobic gram-negati*e bacilli, especially the Enterobacteriaceae and Neisseria. The MIC of ciprofloxacin against these bacteria is usually < 0.microgram/ml, while grampositive bacteria are inhibited at relatively higher concentrations. The spectrum of action E summarized below: Highly susceptible E. coli K. pneumoniae Enterobacter Salmonella typhi other Salmonella Shigella Proteus Neisseria gonorrhoeae N. meningitidis H. influenzae H. ducreyi Campylobacter jejuni Yersinia enterocolitica Vibrio cholerae Clarithromycin: The antimicrobial spectrum of clarithromycin is similar to erythromycin; in addition, it includes Mycobact. avium complex (MAC), other atypical mycobacteria, Mycobact. leprae and some anaerobes but not Bact.fragilis. It is more active against sensitive strains of gram-positive cocci, Moraxella, Legionella, Mycoplasma pneumoniae and Helicobacter pylori. However, bacteria that have developed resistance to erythromycin are resistant to clarithomycin also. Rifabutin:It is related to rifampin in structure and mechanism of action; but less active against M. tuberculi and more active against MAC. Only paial cross resistance occurs between the two. In a dose of 300 mg/ day rifabutin is used for prophylaxis of MAC infection in AIDS patient. For the treatment of established MAC infection, it has been added to ethambutol + clarithromycin/ azithromycin. Pyrazinamide (Z): Chemically similar to INH, pyrazinamide (Z) was developed parallel to it in 1952. 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). It is highly effective during the first 2 months of therapy when inflammatory changes are present. By killing the residual intracellular bacilli it has good &;sterilizing&; activity. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:688,730,742,744