Macrolides
Summary
Bacteriostatic antibiotics (azithromycin, clarithromycin, erythromycin) that bind the 50S ribosomal subunit and inhibit protein synthesis. Cover atypicals, gram-positive cocci, and some gram-negatives.
Detail
Macrolides bind the 23S rRNA of the 50S ribosomal subunit, blocking translocation and inhibiting protein synthesis (bacteriostatic). Spectrum: atypical pneumonia organisms (Mycoplasma, Chlamydia, Legionella), gram-positive cocci, Bordetella pertussis, H. influenzae, and Mycobacterium avium complex (MAC). Resistance via methylation of the 23S rRNA binding site (erm gene). Key adverse effects: MACRO mnemonic — GI Motility issues (prokinetic via motilin), Arrhythmia (QT prolongation, torsades), Cholestatic hepatitis, Rash, eOsinophilia. Significant CYP450 inhibition (erythromycin > clarithromycin >> azithromycin), causing drug interactions with warfarin, statins, and theophylline. Boards: azithromycin = atypical pneumonia, single-dose chlamydia.
Sources
- First Aid for USMLE Step 1 2024
- Sketchy Micro
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