Medicine & USMLE


Anti-Infective Drugs
  1. Vancomycin
  2. Metronidazole
  3. Penicillins
  4. Cephalosporins
  5. Macrolides
  6. Fluoroquinolones
  7. Aminoglycosides
  8. Tetracyclines
  9. Sulfonamides
  10. Rifampin
  11. Isoniazid
  12. Ethambutol
  13. Chloroquine
  14. Acyclovir
  15. Oseltamivir
  16. Azoles
  17. Nystatin
  18. Amphotericin B


Macrolides are drugs recognizable by their common ending of “-thromycin”, including erythromycin, azithromycin, and clarithromycin. Macrolides are antibiotics and can be used clinically to treat a wide spectrum of bacterial infections. Macrolides have the potential to cause QT prolongation, which could lead to the potentially fatal torsades de pointes, so keep an eye on the patient’s cardiac rhythm. Another side effect of taking macrolides is GI distress. Macrolides are hepatotoxic, meaning they can cause liver damage. Closely monitor the patient’s liver enzymes while they are taking the drug.

Key Points

  • Macrolides
    • Key Drugs
      • -thromycin
        • Erythromycin
        • Azithromycin
        • Clarithromycin
    • Mechanism
      • Broad-spectrum antibiotic
        • Bind to the 50S subunit of bacterial ribosomes to inhibit protein synthesis
        • Low doses have a bacteriostatic effect; high doses have a bactericidal effect
        • Given IV or PO; not given IM because it can cause painful tissue irritation
    • Clinical Uses
      • Bacterial Infections
        • Respiratory infections
        • Sinus infections
        • GI infections
        • Skin infections
        • Otitis media
        • Bacterial conjunctivitis
        • Diphtheria
        • STIs
      • Commonly used in patients allergic to penicillins
    • Side Effects and Adverse Reactions
      • Prolonged QT interval
        • May lead to torsade de pointes and sudden cardiac death
      • Hepatotoxicity
        • Liver damage is usually reversible by discontinuation of the drug
        • Monitor liver function tests (AST, ALT), especially if patient is also taking another hepatotoxic medication (e.g. acetaminophen)
      • GI distress
        • Macrolide antibiotics may stimulate motilin receptors in the gut to increase GI motility (causing diarrhea)
        • Nausea, vomiting, diarrhea, abdominal cramping
        • May be taken with food, however antacids should be avoided
      • Clostridium Difficile overgrowth
        • Superinfection caused by broad-spectrum antibiotics destroying existing gut flora to open a niche for C. difficile
        • Report severe diarrhea, as it is the main manifestation of c. diff.
      • Drug interactions
        • Mediated by CYP450 enzyme inhibition
        • Can increases drug levels of warfarin, carbamazepine, and theophylline