Infectious disease

Macrolides song

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Macrolides

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Key points in this song11

Macrolides (azithromycin, clarithromycin, erythromycin) inhibit bacterial protein synthesis by binding the 50S ribosomal subunit and blocking translocation.
Azithromycin is first-line for community-acquired pneumonia in outpatients, atypical pneumonia (Mycoplasma, Chlamydophila, Legionella), and chlamydial urethritis/cervicitis.
Erythromycin is the drug of choice for Bordetella pertussis (whooping cough) and is used as a prokinetic agent by stimulating motilin receptors in the gut.
Clarithromycin is a key component of triple therapy for H. pylori eradication (PPI + clarithromycin + amoxicillin) and is used for MAC prophylaxis and treatment in HIV patients.
Macrolides inhibit CYP3A4 (especially erythromycin and clarithromycin), causing dangerous drug interactions with statins, warfarin, and cyclosporine; azithromycin does NOT inhibit CYP3A
A classic adverse effect of macrolides is QT prolongation, increasing the risk of Torsades de Pointes, particularly when combined with other QT-prolonging drugs.
Erythromycin causes cholestatic hepatitis and is associated with hypertrophic pyloric stenosis when used in neonates under 2 weeks of age.
Macrolides are bacteriostatic, but can be bactericidal at high concentrations; they are not effective against gram-negative enteric rods due to poor outer membrane penetration.
Azithromycin has an exceptionally long half-life (~68 hours) and high tissue penetration, allowing a 5-day or even single-dose treatment course for many infections.
Resistance to macrolides commonly occurs via methylation of the 23S rRNA (erm gene), efflux pumps, or enzymatic inactivation, and cross-resistance with clindamycin (D-zone test positive) is clinically important.