Antimicrobial agents are classified based on chemical structure and proposed mechanism of action, as follows: (1)agents that inhibit synthesis of bacterial cell walls, including the b-lactam class (e.g., penicillins, cephalosporins, and carbapenems) and dissimilar agents such as cycloserine, vancomycin, and bacitracin;(2)agents that act directly on the cell membrane of the microorganism, increasing permeability and leading to leakage of intracellular compounds, including detergents such as polymyxin; polyene antifungal agents (e.g., nystatin and amphotericin B) which bind to cell-wall sterols; and the lipopeptide daptomycin (3)agents that disrupt function of 30S or 50S ribosomal subunits to reversibly inhibit protein synthesis, which generally are bacteriostatic (e.g., chloramphenicol, the tetracyclines, erythromycin, clindamycin, streptogramins, and linezolid); (4)agents that bind to the 30S ribosomal subunit and alter protein synthesis, which generally are bactericidal (e.g., the aminoglycosides);(5)agents that affect bacterial nucleic acid metabolism, such as the rifamycins (e.g., rifampin and rifabutin), which inhibit RNA polymerase, and the quinolones, which inhibit topoisomerases; and (6)the antimetabolites, including trimethoprim and the sulfonamides, which block essential enzymes of folate metabolism.

CLASSIFICATION AND MECHANISM OF ACTION