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Understanding Macrolide Antibiotics

Nov 17, 2024

Lecture on Macrolide Antibiotics

Introduction

  • Macrolide Antibiotics: End with the suffix -thromycin
    • Examples: Erythromycin, Azithromycin, Clarithromycin
    • Erythromycin: The original macrolide
    • Azithromycin and Clarithromycin: Derivatives of Erythromycin

Absorption

  • Good absorption across the body
  • Do not cross the blood-brain barrier
  • Clarithromycin and Azithromycin have better oral absorption

Bacterial Targets

  • Gram-Positive Aerobes:
    • Effective against: Strep pneumoniae, Methicillin-sensitive Staphylococcus aureus (MSSA), Corynebacterium, Diphtheria
    • Not effective against: Enterococcus
  • Gram-Negative Aerobes:
    • Effective against: Moraxella catarrhalis, H. influenza, Legionella, Bordetella pertussis, Gonorrhea, Campylobacter, Salmonella typhi
    • Not effective against: Enterobacteriaceae
  • Others:
    • Effective against: Helicobacter pylori

Clinical Uses

  • Respiratory Infections:
    • Good for pneumonia (especially community-acquired)
    • Azithromycin often combined with third-generation cephalosporins like ceftriaxone
  • Pertussis and Bacterial Bronchitis
  • Sexually Transmitted Infections (STIs)
    • Azithromycin is used for Gonorrhea
  • H. pylori Infections:
    • Clarithromycin is part of the triple therapy
  • Typhoid Fever:
    • Active against Salmonella typhi

Mechanism of Action

  • Bacteriostatic
    • Inhibit protein synthesis by binding to the bacterial 50S ribosomal subunits
    • Similar mechanism to Clindamycin

Side Effects and Risks

  • Hepatotoxicity:
    • Causes hepatitis, cholestatic jaundice, hepatic necrosis, and failure
    • Contraindicated in patients with hepatic dysfunction
  • Gastrointestinal Toxicity:
    • Causes nausea and diarrhea by activating motillin receptors
  • QT Prolongation:
    • Avoid with other QT prolonging drugs
  • Other Adverse Reactions:
    • Anaphylaxis, Stevens-Johnson syndrome, DRESS, pseudomembranous colitis

Specific Drug Interactions

  • Clarithromycin:
    • Interacts with colchicine: Avoid use together
    • Reacts with calcium channel blockers: Increases risk of acute kidney injury

Conclusion

  • Recap on the utility and limitations of macrolides
  • Encouragement to review more lessons on antibiotics in the infectious disease playlist

Note: This lecture covers the key points on the use, mechanism, and side effects of macrolides, which are an important class of antibiotics used to treat a variety of infections.

Full transcript