Azithromycin is a new azalide antimicrobial agent which has a broad spectrum of activity against common lower respiratory tract pathogens including pneumococci, staphylococci, Legionella species, Mycoplasma and Chlamydia species. In particular, it is more active against Haemophilus influenzae than other macrolides. In comparison to other new macrolides, azithromycin achieves higher tissue and intracellular concentrations and these concentrations are sustained for several days after dosing due to a long elimination half-life. The efficacy of azithromycin against lower respiratory tract infections has been proven in several clinical studies. Once-daily dosing with azithromycin, over a 3- or 5- day period was as effective as a 10-day course of other commonly used antibiotics such as amoxycillin/clavulanic acid, erythromycin or cefaclor in lower respiratory tract infections. Azithromycin short-course therapy may offer an advantage in terms of patient compliance and the duration of treatment.