Chemotherapy Study Notes

The History of Chemotherapy

Introduction to Antibiotics

An antibiotic is defined as a substance produced by a microbe that, in small amounts, inhibits the growth of another microbe. Understanding antibiotics is crucial in the context of chemotherapy.

Representative Sources of Antibiotics
  • Streptomyces: A significant source of antibiotics. This genus produces several well-known antibiotics such as:
      - Streptomycin
      - Erythromycin
      - Chloramphenicol
    These antibiotics are effective against a wide range of infections, including bacterial, fungal, and respiratory system infections.
Categories of Antibiotics

  1. Natural Penicillins:
       - Examples include:
         - Penicillin G: Administered by injection.
         - Penicillin V: Administered orally (orally active).
       - Spectrum: Have a narrow spectrum of activity and are susceptible to penicillinases, which are enzymes that can inactivate penicillin.

  2. Polypeptide Antibiotics:
       - Vancomycin: Considered a last resort antibiotic against antibiotic-resistant strains like Methicillin-resistant Staphylococcus aureus (MRSA).
       - Teixobactin: Functions against resistant Gram-positive bacteria.

  3. Antimycobacterial Antibiotics:
       - Isoniazid: Inhibits the synthesis of mycolic acid, which is crucial for the cell wall of mycobacteria.

Spectrum of Antimicrobial Activity
  • Narrow-Spectrum Antibiotics: Target a limited range of microbial types.
  • Broad-Spectrum Antibiotics: Effective against a broad range of Gram-positive and Gram-negative bacteria.

Mechanism of Action of Antimicrobial Drugs

Antimicrobial drugs work primarily through two mechanisms:

  • Bactericidal: These drugs kill microbes directly.
  • Bacteriostatic: These drugs prevent microbes from growing.
Specific Actions of Antimicrobial Drugs
  • Penicillins: Prevent the synthesis of peptidoglycan, a vital component of bacterial cell walls, leading to cell lysis.
  • Inhibitors of Protein Synthesis:
      - Target bacterial 70S ribosomes, which are distinct from the 80S ribosomes of eukaryotic cells.
      - Examples include:
        - Chloramphenicol: Binds to the 50S subunit of the ribosome and inhibits peptide bond formation; broad spectrum.
        - Aminoglycosides: Such as Streptomycin.
Injury to Cell Membranes
  • Polymyxin B: Disrupts bacterial cell membrane integrity and is often combined with bacitracin and neomycin in nonprescription ointments.