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Azithromycin, clarithromycin, and telithromycin

Amy L Graziani, PharmD
Section Editor
David C Hooper, MD
Deputy Editor
Sheila Bond, MD


Azithromycin (Zithromax) and clarithromycin (Biaxin) are macrolide antibiotics that are used in the treatment of community-acquired respiratory tract infections, particularly pneumonia. They are derivatives of the older macrolide antibiotic, erythromycin. Structural modifications of erythromycin cause a change in the spectrum of activity, dosing, and administration of the newer macrolides and ketolides. Telithromycin (Ketek) is the first member of the ketolide class of antimicrobials, which is related to the macrolide class. Concerns about postmarketing reports of hepatotoxicity and exacerbations of myasthenia gravis have led to significant restrictions on the use of telithromycin. (See 'Warnings about telithromycin' below.)

The spectrum of activity, mechanisms of action and resistance, pharmacokinetics, interactions with other drugs, and adverse effects of these newer macrolide antibiotics will be reviewed here. The use of these drugs for community-acquired pneumonia is discussed separately. (See "Treatment of community-acquired pneumonia in adults in the outpatient setting" and "Treatment of community-acquired pneumonia in adults who require hospitalization".)

The macrolides are sometimes used for their anti-inflammatory effects. This is discussed in detail separately. (See "Cystic fibrosis: Overview of the treatment of lung disease", section on 'Macrolide antibiotics' and "Chronic lung transplant rejection: Bronchiolitis obliterans", section on 'Treatment' and "Diffuse panbronchiolitis", section on 'Macrolide antibiotics'.)


The antibacterial mechanism of action of the newer macrolides is similar to that of erythromycin. They bind to the 50S subunit of bacterial ribosomes, leading to inhibition of transpeptidation, translocation, chain elongation, and, ultimately, bacterial protein synthesis [1,2].

Clarithromycin has the same macrolide 14-membered lactone ring as erythromycin; the only difference is that, at position six, a methoxy group replaces the hydroxyl group [1]. Azithromycin, in comparison, has a 15-membered ring and a methyl-substituted nitrogen replacing the 9A carbonyl group. For this reason, azithromycin is more precisely referred to as an azalide rather than a macrolide [2-4].

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Literature review current through: Nov 2017. | This topic last updated: May 31, 2017.
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