Does it matter whether we use a bactericidal antibiotic or a bacteriostatic one? Surely, the bactericidal one would be more effective, right? The answer is not that simple.
Bactericidal = antibiotics that kill bacteria
Bacteriostatic = antibiotics that inhibit the growth of bacteria (i.e. prevent the bacteria from continuing to grow/proliferate) without killing bacteria in vitro OR it is able to kill the bacteria in vitro but at a slower rate than bactericidal agent does.
– there is thought out there that bacteriostatic agents require more activity from the immune system to eradicate the bacteria (this has not been studied well in literature and there is no data to support or negate this hypothesis).
Bactericidal drugs: Bacteriostatic drugs:
Aminoglycosides Glycylcyclines (tigecycline)
Beta-lactams Lincosamides (clindamycin)
Fluoroquinolones Macrolides (azithromycin, fidaxomicin)
Glycopeptides (vancomycin) Oxazolidinones (linezolid, tedizolid)
Lipopeptides (daptomycin) Streptogramins (quinipristin/dalfopristin)
Nitroimidazoles/nitrofurans Sulphonamides (sulfamethoxazole)
*Keep in mind – bactericidal and bacteriostatic effects depend on several factors, including the amount of:
1) bacterial inoculum: the burden of bacteria can change the antibiotic’s properties
2) the pathogen: certain antibiotics are “cidal” to certain pathogens, while “static” to others
a) vancomycin is “cidal” against staph and strep, but “static” against enterococci
b) azithromycin is “cidal” against strep, but “static” against staph
c) linezolid may be “cidal” against strep, but “static” against staph/enterococci
3) medium/location of infection: certain antibiotics are more effective in certain parts of the body (IV vancomycin doesn’t penetrate GI mucosa, tigecycline doesn’t achieve high concentrations in the bloodstream, etc.)
Why could this be potentially clinically irrelevant?
A systematic review published in CID in 2017 looked at all the 59 randomized-controlled trials on clinical outcomes when using bactericidal vs. bacteriostatic agents. They found that 49 (81%) of the trials showed no differences in clinical outcomes when using “cidal” vs. “static” agents.
Similarly, studies demonstrated that using linezolid (a bacteriostatic agent) against MRSA was non-inferior to vancomycin (a bactericidal agent) against MRSA.
Because clinical outcomes depend on 3 factors:
- The host
- The pathogen
- The drug (with many internal factors coming into play as listed below
- Antibiotics can be bacteriostatic for some pathogens and bactericidal for others
- Clinical outcomes depend on a variety of factors and the bactericidal property of an antibiotic ultimately appears to have little clinical relevance.
- Nemeth, J., Oesch, G., and Kuster, S.P. 2015. Bacteriostatic versus bactericidal antibiotics for patients with serious bacterial infections: systematic review and meta-analysis. Journal of antimicrobial chemotherapy. 70:382-395.
- French, G.L. 2006. Bactericidal agents in the treatment of MRSA infections – the potential role of daptomycin. Journal of Antimicrobial Chemotherapy. 58 (6): 1107-1117.
- Wald-Dicker, N, Holtom, P, and Spellberg, B. 2017. Busting the myth of “static vs. cidal”: A systemic literature review. CID
- Panckey, G.A. and Sabath, L.D. 2004. Clinical relevance og bacteriostatic versus bactericidal mechanisms of action in the treatment of gram-positive bacterial infections. CID, 38(6): 864-870.