[Antibiotic treatment of cystic fibrosis].

Lower respiratory tract superinfection is nearly constant in cystic fibrosis and has a significant impact on mortality. The three organisms which most often colonize the bronchial tree are Staphylococcus aureus, Haemophilus influenzae and Pseudomonas aeruginosa. The latter organism is found in 70% to 90% of older cystic fibrosis patients. P. aeruginosa infections are remarkably persistent and cause severe, extensive lung damage. Antimicrobial therapy is indicated in patients with clinical symptoms (fever, weight loss, changes in sputum and auscultation) and should be selected on the basis of cytobacteriologic studies of sputum. Oral antibiotics are usually successful in eradicating S. aureus and H. influenzae. Conversely, intravenous therapy is required in most cases of P. aeruginosa infection. Fifteen-day courses are given repeatedly, either on a routine basis every three months, or whenever new clinical symptoms develop. Antimicrobials usually fail to eradicate P. aeruginosa even when significant clinical improvement occurs. Two-drug therapy and judicious use of the various available anti-microbial agents should delay development of resistant strains, an event which is nearly inevitable as antimicrobial treatments are repeated.