AZITHROMYCIN AND LOWER RESPIRATORY-TRACT INFECTIONS

Azithromycin is a molecule of the macrolide family, belonging to the azalides class. Several of its caracteristics allow for its use in the treatment of the community-acquired lower respiratory tract infections. Commonly isolated pathogens in branchial infections are most frequently H, influenzae, S. pneumoniae, M. catarrhalis, C. pneumoniae and M. pneumoniae, and more rarely or in the context of a particular background, S, aureus, Gram negative bacteria and L, pneumophila. MIC(90) of these germs is generally low or slightly elevated, displaying an inhibitory activity of the azithromycin on these bacteria. Nevertheless, the frequency of macrolide-resistant S. pneumoniae is not negligible and this germ must be considered as inconstantly susceptible to the macrolide family. Pharmacokinetics studies evidenced from high to very high azithromycin concentrations in the pulmonary tissues, reaching values well above MIC of pathogens commonly isolated. Given the long half-life, these concentrations persist a long time after oral administration. As azithromycin concentrates much in polymorphonuclear leucocytes, they release azithromycin after having migrated into the infectious site by chimiotactism, thus allowing to increase the antibiotic concentration at infection site. These requirements have been confirmed in vivo in animal models and in clinical studies. Two experimental models on macrolide susceptible S. pneumoniae, and Ii. influenzae evidenced a better activity of azithromycin in comparison to other macrolides tested against these two germs. Clinical trials testing the azithromycin given at the total dose of 1.5 g in 5 to 3 days for bronchitis (acute or in superinfection during chronic bronchitis of the type 1 Anthonisen stage) displayed an equivalence in terms of efficacy with regard to comparative molecules. Some trials done in intra and extracellular bacterial pneumopathies report cure-improvement results around 90 %. In practice, if attention should be drawn on S. pneumoniae which can be resistant to azithromycin, its activity on other germs frequently seen in lower respiratory tract infections, its peculiar pharmacokinetic profile to attain high tissular concentrations for a very prolonged period allows its use for treating infections in patients who do not have severe comorbidity factors with a simple treatment for 5 days, may be even 3 days.