Erythromycin was the first macrolide used clinically. Newer examples include clarithromycin and azithromycin.

Mechanism of action

Macrolides act by blocking the 50s subunit of the bacterial ribosome which in turn inhibits bacterial protein synthesis.

Mechanism of resistance
  • Post-transcriptional methylation of the 23S bacterial ribosomal RNA

Adverse effects

  • Gastrointestinal side-effects are common. Nausea is less common with clarithromycin than erythromycin
  • Cholestatic jaundice: risk may be reduced if erythromycin stearate is used
  • P450 inhibitor


Common interactions
  • Statins should be stopped whilst taking a course of macrolides. Macrolides inhibit the cytochrome P450 isoenzyme CYP3A4 that metabolises statins. Taking macrolides concurrently with statins significantly increases the risk of myopathy and rhabdomyolysis.