Clarithromycin is a new macrolide with a broad spectrum of activity against Gram-positive cocci,Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma, Chlamydiaand selectedMycobacteria, Legionellaand protozoa. The drug has a half-life of more than 4 hours and thus can be administered in a twice daily schedule. Clarithromycin is well-tolerated in children and adults and produces fewer gastrointestinal side effects than erythromycin. High concentrations of the drug are achieved in plasma and in cells and tissues including tonsil, lung and middle ear fluids. Clinical efficacy has been demonstrated in randomized multicenter trials of infants and children with acute otitis media, streptococcal pharyngitis and infections of skin and skin structures. Results of these comparative trials with randomized patients receiving clarithromycin or standard drugs identified equivalent clinical and bacteriologic outcomes. A higher rate of eradication of group AStreptococcusfrom the pharynx was achieved with clarithromycin than with penicillin VK. The potential advantages provided by high concentrations of clarithromycin in cells and tissues such as more rapid clinical improvement or shortened dosage schedules are still to be identified.