3rd August 2023

Macrolides

Mechanism of action

Bacteriostatic drugs inhibit bacterial growth by binding to the 50s subunit of the bacterial ribosome, rather than directly killing the bacteria.

Spectrum of activity

Macrolides have a similar spectrum of activity to many penicillins, so they are a common alternative agent for patients allergic to penicillin.

Common indications include respiratory tract infections (including atypical pneumonia(, skin and soft tissue infections, and gastroenteritis caused by Campylobacter species.

The three most commonly used macrolides are erythromycin, clarithromycin and azithromycin. Claithromycin is derived from erythromycin and has a broader spectrum of activity. Azithromycin has not as good Gram positive activity but better Gram negative activity. It has a long half life, so it’s amenable to once daily dosing.

Important side effects, interactions and monitoring

GI upset is a common side effect, especially with erythromycin and clarithromycin; this is dose-dependent, so it may be avoided by giving lower doses when possible. This is also a therapeutic effect of erythromycin, which can treat vomiting caused by gastric stasis.

Macrolides are also known to be QT interval prolongers.