Antibiotics: Classification, Killing Mechanisms, and Superinfection

• Beta-lactams: Inhibit bacterial cell wall synthesis. Examples: Penicillins (Amoxicillin), Cephalosporins (Ceftriaxone), Carbapenems (Imipenem).
• Macrolides: Inhibit bacterial protein synthesis. Examples: Erythromycin, Azithromycin, Clarithromycin.
• Aminoglycosides: Inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit. Examples: Gentamicin, Amikacin.
• Tetracyclines: Inhibit bacterial protein synthesis. Examples: Doxycycline, Minocycline.
• Fluoroquinolones: Inhibit bacterial DNA replication. Examples: Ciprofloxacin, Levofloxacin.
• Sulfonamides: Inhibit folic acid synthesis. Examples: Sulfamethoxazole, Sulfisoxazole.
• Glycopeptides: Inhibit cell wall synthesis. Examples: Vancomycin, Teicoplanin.
• Lincosamides: Inhibit protein synthesis. Example: Clindamycin.

Antibiotics work by targeting essential bacterial processes such as:

• Cell Wall Synthesis: Beta-lactams (e.g., Penicillins) inhibit bacterial cell wall formation.
• Protein Synthesis: Macrolides and Aminoglycosides prevent protein synthesis in bacteria.
• DNA Replication: Fluoroquinolones (e.g., Ciprofloxacin) inhibit DNA gyrase.
• Folic Acid Metabolism: Sulfonamides inhibit the synthesis of folic acid necessary for bacterial growth.

1. Time-Dependent Killing

Time-dependent killing refers to antibiotics whose efficacy is related to the duration of time the drug concentration stays above the minimum inhibitory concentration (MIC) of the pathogen.

• Examples: Beta-lactams (e.g., Penicillin).
• Clinical Importance: Dosing strategies for time-dependent killers focus on maintaining drug levels above the MIC for a prolonged period, often requiring frequent dosing.

2. Concentration-Dependent Killing

Concentration-dependent killing refers to antibiotics whose efficacy is maximized by achieving a high peak drug concentration relative to the MIC.

• Examples: Aminoglycosides (e.g., Gentamicin), Fluoroquinolones (e.g., Ciprofloxacin).
• Clinical Importance: For concentration-dependent antibiotics, high doses are often administered to maximize efficacy, typically with less frequent dosing.

1. Definition

A superinfection is a new infection that occurs during or after the treatment of an initial infection, typically caused by opportunistic pathogens that overgrow when normal flora is disrupted.

2. Causes of Superinfection

• Broad-spectrum antibiotics: Disrupt the normal microbial flora, leading to overgrowth of resistant organisms.
• Examples of drugs causing superinfection:
  • Penicillins (e.g., Amoxicillin)
  • Cephalosporins
  • Clindamycin (e.g., C. difficile infections)

3. Treatment

• Discontinuing the causative antibiotic: If the superinfection is due to the initial antibiotic therapy.
• Targeted antibiotic therapy: Based on culture and sensitivity testing.
• For C. difficile: Use Vancomycin or Fidaxomicin.
• For fungal superinfections: Use antifungals like Fluconazole.
• Restoration of normal flora: Probiotics may be used in some cases to restore microbial balance.