Bacteriostatic versus Bactericidal Mechanisms of Action in the Treatment of Gram-Positive Bacterial Infections
Definitions:
“”Bacteriostatic” means that the agent prevents the growth of bacteria (i.e., it keeps them in the stationary phase of growth), and “Bactericidal” means that it kills bacteria. In reality, there are not 2 pure categories of antimicrobial agents (one that exclusively kills bacteria and another that only inhibits growth). Rather, those agents that are called “bactericidal” usually fail to kill every organism (if, for instance, the inoculum is large) within 18–24 h after the test, and most so-called “bacteriostatic” agents kill some bacteria within the 18–24 h after the test—often more than 90%–99% of the inoculum, but not enough (>99.9%) to be called “bactericidal.” The in vitro microbiological determination of whether an antibacterial agent is bactericidal or bacteriostatic may be influenced by growth conditions, bacterial density, test duration, and extent of reduction in bacterial numbers. The clinical definition is even more arbitrary. Most antibacterials are better described as potentially being both bactericidal and bacteriostatic.” Clin Infect Dis (2004) 38 (6): 864-870.
Clinical significance:
“The distinction between bactericidal and bacteriostatic agents appears to be clear according to the in vitro definition, but this only applies under strict laboratory conditions and is inconsistent for a particular agent against all bacteria. The distinction is more arbitrary when agents are categorized in clinical situations. The supposed superiority of bactericidal agents over bacteriostatic agents is of little relevance when treating the vast majority of infections with gram-positive bacteria, particularly in patients with uncomplicated infections and non-compromised immune systems. Bacteriostatic agents (e.g., chloramphenicol, clindamycin, and linezolid) have been effectively used for treatment of endocarditis, meningitis, and osteomyelitis—indications that are often considered to require bactericidal activity. Although bacteriostatic/bactericidal data may provide valuable information on the potential action of antibacterial agents in vitro, it is necessary to combine this information with pharmacokinetic and pharmacodynamic data to provide more meaningful prediction of efficacy in vivo. The ultimate guide to treatment of any infection must be clinical outcome.” Clin Infect Dis (2004) 38 (6): 864-870.
Reference
Clin Infect Dis (2004) 38 (6): 864-870.