AZITHROMYCIN - REVIEW OF KEY CHEMICAL, PHARMACOKINETIC AND MICROBIOLOGICAL FEATURES

One of the chemical features that distinguishes the 15-membered ring a zalide azithromycin from the 14-membered ring macrolide compound eryth romycin is the former's increased stability at acid pH. Azithromycin a lso differs pharmacokinetically from erythromycin, an important featur e being azithromycin's ability to achieve high tissue concentrations, with the agent being delivered to the sites of infection by direct upt ake and by targeted delivery via phagocytes. High tissue concentration s are maintained for prolonged periods because of azithromycin's long half-life, leading to once-daily dosing for 3 or 5 days. Notable micro biological features of azithromycin are in-vitro activity against many pyogenic bacteria (e.g. Neisseria gonorrhoeae and Moraxella catarrhal is), as well as organisms against which beta-lactam antibiotics are us ually ineffective (e.g. Legionella and Chlamydia spp.), organisms that are resistant to benzylpenicillin and erythromycin (e.g. Haemophilus influenzae) and organisms for which satisfactory therapy is limited (e .g. Toxoplasma gondii and the Mycobacterium avium-intracellulare compl ex). These properties of azithromycin suggest that it might be a usefu l agent for the treatment of a wide range of bacterial infections.