Lecture: Antibiotics and Their Mechanisms

Categories of Antibiotics

1. Plasma Membrane Injury

   • Polymyxin B is a common antibiotic used for plasma membrane injury.
   • Lipopeptide is effective for gram-positive bacteria but is less common.
   • Antibiotics targeting plasma membranes are hard to develop due to potential human cell damage.
   • Neosporin contains polymyxin B.

2. Nucleic Acid Synthesis Inhibitors

   • Important drugs include Rifampin (also known as Ripa myosin) that inhibit mRNA synthesis and transcription.
   • Quinolones and fluoroquinolones inhibit DNA gyrase, preventing DNA replication.
     • Ciprofloxacin (Cipro): used prophylactically during anthrax exposure; common treatment for urinary tract infections.
     • Resistance to ciprofloxacin can develop rapidly.

3. Competitive Inhibitors of Metabolism

   • Focus on folic acid pathway inhibition.
   • Sulfonamides:
     • Bind to enzymes in the folic acid synthesis pathway, resembling para-aminobenzoic acid to prevent its binding.
   • Trimethoprim:
     • Resembles dihydrofolic acid and inhibits another enzyme in the pathway.
   • Both drugs prevent nucleotide synthesis by blocking folic acid production.

Antibiotics and Viral Infections

• Antibiotics do not work on viruses because:

  • Viruses lack cell walls, do not perform protein synthesis, lack plasma membranes, and do not produce DNA/RNA or folic acid.
  • Antibiotics target structures and processes found in bacteria, not viruses.

• Misconceptions:

  • People often misattribute improvement while taking antibiotics to the medication, rather than the natural course of the viral illness.
  • True causation should not be confused with mere correlation.

• When to Consider Antibiotics for Viral Infections:

  • In cases of pre-existing conditions or risk of secondary bacterial infections (e.g., bacterial pneumonia), prophylactic antibiotics may be necessary.

Conclusion and Important Considerations

• Educating patients on the ineffectiveness of antibiotics for viral infections is crucial, despite challenges.
• Avoid over-prescribing antibiotics to prevent antibiotic resistance.
• Upcoming lectures will cover the impact of environmental presence of antibiotics on resistance.
• Historical importance: Antibiotics have significantly reduced infant mortality and increased life expectancy.

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These notes cover the key points and ideas from the lecture on antibiotics, their categories, their effectiveness, and common misconceptions. It is essential to understand the mechanisms of antibiotics to make informed decisions in medical practice, particularly regarding viral infections.