What is the difference between bacteriocidal and bacteriostatic (bacterial growth inhibiting) antibiotics?

From the Guidelines

Bactericidal antibiotics, such as penicillins, cephalosporins, carbapenems, aminoglycosides, fluoroquinolones, vancomycin, daptomycin, and metronidazole, are generally preferred over bacteriostatic antibiotics for severe infections, as they directly kill bacteria, whereas bacteriostatic antibiotics, including tetracyclines, macrolides, lincosamides, sulfonamides, chloramphenicol, and linezolid, inhibit bacterial growth, allowing the immune system to clear the infection 1. The distinction between bactericidal and bacteriostatic antibiotics is crucial in clinical practice, as bactericidal antibiotics are often necessary for severe infections, immunocompromised patients, endocarditis, meningitis, and osteomyelitis, where rapid bacterial killing is essential.

• Bactericidal antibiotics work by disrupting cell wall synthesis, bacterial DNA, or protein synthesis at the 50S ribosomal subunit, resulting in the direct killing of bacteria.
• Bacteriostatic antibiotics, on the other hand, inhibit protein synthesis at the 30S ribosomal subunit or interfere with metabolic pathways, allowing the immune system to clear the infection. Some bacteriostatic antibiotics, such as clindamycin, can be bactericidal at higher concentrations or against certain organisms, highlighting the complexity of antibiotic mechanisms of action 2. In terms of specific antibiotics,
• penicillins, such as amoxicillin and piperacillin,
• cephalosporins, such as ceftriaxone and cefazolin,
• carbapenems, such as meropenem and imipenem,
• aminoglycosides, such as gentamicin and tobramycin,
• fluoroquinolones, such as ciprofloxacin and levofloxacin,
• vancomycin,
• daptomycin, and
• metronidazole are considered bactericidal 1. In contrast,
• tetracyclines, such as doxycycline and minocycline,
• macrolides, such as azithromycin and erythromycin,
• lincosamides, such as clindamycin,
• sulfonamides, such as trimethoprim-sulfamethoxazole,
• chloramphenicol, and
• linezolid are considered bacteriostatic 2.

From the FDA Drug Label

The results of time-kill studies have shown linezolid to be bacteriostatic against enterococci and staphylococci For streptococci, linezolid was found to be bactericidal for the majority of strains. The tetracyclines are primarily bacteriostatic and are thought to exert their antimicrobial effect by the inhibition of protein synthesis. The bactericidal action of vancomycin results primarily from inhibition of cell-wall biosynthesis.

Bacteriocidal vs Bacteriostatic Antibiotic List:

• Bactericidal: + Vancomycin 3 + Linezolid (against streptococci) 4
• Bacteriostatic: + Linezolid (against enterococci and staphylococci) 4 + Doxycycline 5

From the Research

Bacteriocidal vs Bacteriostatic Antibiotics

• The distinction between bactericidal and bacteriostatic agents is not always clear-cut, as it can vary depending on the specific bacteria and laboratory conditions 6, 7.
• Bacteriostatic agents, such as chloramphenicol, clindamycin, and linezolid, have been effectively used to treat serious infections like endocarditis, meningitis, and osteomyelitis 6.
• Studies have shown that bacteriostatic agents like linezolid and tigecycline are clinically non-inferior to bactericidal agents in treating multiple infections, including pneumonia, intra-abdominal infections, and skin and soft tissue infections 7, 8.

Examples of Bacteriostatic and Bactericidal Antibiotics

• Bacteriostatic agents:
  • Chloramphenicol
  • Clindamycin
  • Linezolid
  • Tigecycline
• Bactericidal agents:
  • Aminoglycosides (e.g., gentamicin, tobramycin)
  • Fluoroquinolones (e.g., ciprofloxacin, levofloxacin)
  • Penicillins (e.g., amoxicillin, penicillin G)
  • Cephalosporins (e.g., ceftriaxone, cefepime)

Clinical Significance of Bactericidal vs Bacteriostatic Antibiotics

• The choice between bactericidal and bacteriostatic antibiotics may not be as critical as previously thought, as clinical outcomes are often similar 6, 8.
• However, certain infections like endocarditis, neutropenia, and bacteraemia may still require bactericidal agents 7.
• The combination of bactericidal and bacteriostatic agents may not always be antagonistic, and some combinations like linezolid and rifampicin are already being used 7.