Azithromycin vs. Clarithromycin: Choosing the Right Macrolide

Both are macrolides that inhibit the bacterial 50S ribosomal subunit, blocking protein synthesis. Key pharmacologic differences drive clinical selection:

Feature	Azithromycin	Clarithromycin
Half-life	68 hrs (tissue)	3–7 hrs
Dosing	Once daily (3–5 day course)	BID (7–14 days)
Gram-positive	+++	+++
Gram-negative (H. influenzae, M. catarrhalis)	++	+++
Atypicals (Legionella, Mycoplasma, Chlamydia)	+++	+++
H. pylori	Weak	+++ (regimen cornerstone)
MAC Prophylaxis (HIV)	+++ (weekly)	+++ (BID)
CYP3A4 Inhibition	Minimal	Strong (major DDIs: statins, DOACs, CCBs, tacrolimus)
Hepatotoxicity	Higher risk (cholestatic)	Lower
QT Prolongation	Low-moderate	Moderate
Generic Cost	Higher	Lower

Clinical Pearls

• CAP: Both effective; azithromycin preferred for adherence and atypical coverage.
• H. pylori: Clarithromycin essential (unless resistance documented).
• Drug Interactions: Avoid clarithromycin with strong CYP3A4 substrates; azithromycin is safer.
• Pregnancy: Azithromycin Category B; clarithromycin Category C (animal fetal loss).
• Resistance: Macrolide resistance rising (erm, mef genes); susceptibility testing if treatment fails.

Select based on infection type, comorbidities, comedications, and local resistance patterns.