Effect on Bacteria
Because of differences in the mechanisms by which antibiotics affect bacteria, the clinical use of antibacterials may have very different effects on bacterial agents, leading to an endpoint of either inactivation or actual death of the bacteria.
Bactericidal drugs are those that kill target organisms. Examples of bactericidal drugs include aminoglycosides, cephalosporins, penicillins, and quinolones.
Bacteriostatic drugs inhibit or delay bacterial growth and replication. Examples of such include tetracyclines, sulfonamides, and macrolides.
Some antibiotics can be both bacteriostatic and bactericidal, depending on the dose, duration of exposure and the state of the invading bacteria. For example, aminoglycosides, fluoroquinolones, and metronidazole exert concentration-dependent killing characteristics; their rate of killing increases as the drug concentration increases.