Clarithromycin, sold under the brand name Biaxin among others, is an antibiotic used to treat various bacterial infections. This includes strep throat, pneumonia, skin infections, H. pylori infection, and Lyme disease, among others. Clarithromycin can be taken by mouth as a tablet or liquid or can be infused intravenously.

Common side effects include nausea, vomiting, headaches, and diarrhea. Severe allergic reactions are rare. Liver problems have been reported. It may cause harm if taken during pregnancy. It is in the macrolide class and works by slowing down bacterial protein synthesis. Clarithromycin resistance is already a major challenge to healthcare systems and such resistance is spreading, leading to recommendations to test the susceptibility of pathogenic organisms to the antibiotic before commencing clarithromycin therapy.

Clarithromycin was developed in 1980 and approved for medical use in 1990. It is on the World Health Organization's List of Essential Medicines. Clarithromycin is available as a generic medication. It is made from erythromycin and is chemically known as 6-O-methylerythromycin.

Clarithromycin is primarily used to treat a number of bacterial infections including pneumonia, Helicobacter pylori, and as an alternative to penicillin in strep throat. Other uses include cat scratch disease and other infections due to Bartonella, cryptosporidiosis, as a second line agent in Lyme disease and toxoplasmosis. It may also be used to prevent bacterial endocarditis in those who cannot take penicillin. It is effective against upper and lower respiratory tract infections, skin and soft tissue infections and helicobacter pylori infections associated with duodenal ulcers.^{[citation needed]}

Aerobic Gram-positive bacteria

Aerobic Gram-negative bacteria

Helicobacter

Mycobacteria