Pharm 101: Azithromycin

Class

Macrolide antibiotic

Pharmacodynamics

• Inhibits bacterial protein synthesis by binding to 50S ribosomal RNA

Pharmacokinetics

• PO or IV administration
• Rapidly absorbed orally
• Penetrates into most tissues (except CSF) and phagocytic cells extremely well
  • Tissue concentrations exceed serum concentrations 10-100 fold
  • Drug is slowly released from tissues (tissue half life 2-4 days), elimination half-life thus ~3 days
  • Permits infrequent dosing and short courses of treatment
• No CYP interactions, unlike erythromycin and clarithromycin

Antimicrobial activity of macrolide antibiotics

• Gram positive organisms e.g. pneumococci, strep, staph
• Mycoplasma pneumoniae, L pneumophila, Chlamydophila pneumoniae, Listeria monocytogenes
• Gram negative organisms e.g. neisseria, bordatella pertussis, campylobacter
• Treponema pallidum
• Azithromycin specifically:
  • Highly active against Chlamydophila sp.
  • Active against Toxoplasma gondii
  • Slightly less active against staph and strep
  • Slightly more active against H influenzae

Adverse effects

• Prolonged QT interval

Further reading

• Buttner R. Pharm 101: Erythromycin. LITFL

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 820, 824