Amoxicillin vs Azithromycin: what is the difference?

How they differ

Both are common antibiotics and they belong to different classes with different targets. Amoxicillin is a penicillin: it carries the four-membered beta-lactam ring that blocks bacterial cell wall construction, which is why it is inactivated by beta-lactamase enzymes and why it is often paired with clavulanic acid. Azithromycin is a macrolide, a large 15-membered ring that binds the bacterial ribosome and stops protein synthesis. Azithromycin accumulates inside tissue and clears very slowly, which is why a short course keeps working for days after the last dose, while amoxicillin clears in hours and must be taken repeatedly. Azithromycin is far the larger molecule at 749.0 against 365.4. Penicillin allergy is the usual reason a prescriber reaches for one class over the other.

Side by side

Common questions

What is the difference between Amoxicillin and Azithromycin?

Both are common antibiotics and they belong to different classes with different targets. Amoxicillin is a penicillin: it carries the four-membered beta-lactam ring that blocks bacterial cell wall construction, which is why it is inactivated by beta-lactamase enzymes and why it is often paired with clavulanic acid. Azithromycin is a macrolide, a large 15-membered ring that binds the bacterial ribosome and stops protein synthesis.

Is Amoxicillin bigger than Azithromycin?

Azithromycin is the heavier molecule, 749 g/mol against 365.4 g/mol for Amoxicillin. Amoxicillin is C16H19N3O5S and Azithromycin is C38H72N2O12.