Macrolides

Macrolides — azithromycin, erythromycin, clarithromycin — work by binding the 50S ribosomal subunit of bacteria, blocking protein synthesis. This makes them bacteriostatic at standard doses. They cover gram-positive cocci, atypical organisms (Mycoplasma pneumoniae, Chlamydia, Legionella), and some gram-negatives like H. influenzae. Azithromycin is the most commonly prescribed; its long tissue half-life allows the classic Z-pack (5-day course). Erythromycin is used in neonatal eye prophylaxis (0.5% ophthalmic ointment applied within 1 hour of birth to prevent gonococcal ophthalmia neonatorum). A critical adverse effect is QT prolongation, which increases the risk of torsades de pointes — always assess the client's cardiac history and concurrent QT-prolonging medications before administration. GI distress (nausea, abdominal cramping, diarrhea) is the most common side effect, especially with erythromycin, because macrolides stimulate motilin receptors in the gut. Hepatotoxicity can occur; monitor for jaundice, dark urine, and elevated liver enzymes. Erythromycin and clarithromycin are potent CYP3A4 inhibitors, creating dangerous drug interactions — particularly with warfarin, statins, and carbamazepine (azithromycin has minimal CYP3A4 activity). Teach the client to report palpitations, syncope, or severe diarrhea immediately.