What is the Difference Between Clarithromycin and Erythromycin?

Clarithromycin and erythromycin are both macrolide antibiotics used to treat various bacterial infections. They share similarities, but there are some differences between the two medications:

1. Pharmacokinetics: Clarithromycin has a longer serum half-life and better tissue penetration than erythromycin. This allows for twice-a-day dosing for most common infections, while erythromycin has a shorter half-life.
2. Activity against pathogens: Clarithromycin is several-fold more active in vitro than erythromycin against gram-positive bacteria, while azithromycin is 2- to 4-fold less potent. Both clarithromycin and erythromycin are effective for the treatment of common respiratory and skin infections, as well as nongonococcal urethritis.
3. Pregnancy category: Both erythromycin and azithromycin are pregnancy category B drugs, while clarithromycin is a category C drug.
4. Tolerability and drug interactions: Compared with erythromycin, clarithromycin and azithromycin offer improved tolerability. However, clarithromycin is more similar to erythromycin in pharmacokinetic measures such as half-life, tissue distribution, and drug interactions.
5. Efficacy in community-acquired pneumonia: Erythromycin was found to be less effective compared with clarithromycin for the treatment of community-acquired pneumonia (CAP) in a systematic review and meta-analysis. The increased efficacy of clarithromycin may result from a longer half-life, increased plasma concentration, and increased activity against a wider spectrum of pathogens related to CAP, such as H. influenzae.

Comparative Table: Clarithromycin vs Erythromycin

Clarithromycin and erythromycin are both antibiotics used to treat bacterial infections, but they have some differences in their pharmacokinetic properties, antibacterial spectrum, and tolerability. Here is a comparison table of the differences between clarithromycin and erythromycin:

Clarithromycin is an acid-stable analogue of erythromycin with a methoxy substitution at C-6. It has been shown to have an antibacterial spectrum and pharmacokinetic profiles superior to that of erythromycin. Both clarithromycin and azithromycin, another macrolide antibiotic, offer improved tolerability compared to erythromycin. However, clarithromycin is more similar to erythromycin in pharmacokinetic measures such as half-life, tissue distribution, and drug interactions.