J Clin Microbiol. 2011 Jul;49(7):2772-3. Epub 2011 May 4.

randomized, placebo-controlled multicenter trial

260 children and adolescents with CF. The study enrolled relatively healthy children and adolescents with CF but uninfected with P. aeruginosa

Respiratory tract specimens were obtained at baseline, day 84, and day 168

azithromycin

At baseline, 74% of both azithromycin and placebo participants harbored S. aureus (3) and 4.6% of participants harbored SCV S. aureus. There was no association between treatment with azithromycin and emergence of SCV S. aureus. Treatment-emergent azithromycin-resistant non-SCV strains of methicillin-susceptible and/or methicillin-resistant S. aureus were detected in 37% of azithromycin and 11% of placebo participants (P < 0.001) but there was no association between azithromycin resistance and SCVs. Among 57 participants with azithromycin-resistant non-SCV S. aureus at baseline, 4 harbored SCV strains, and among 135 participants without azithromycin resistance, 8 harbored SCV strains (difference in proportions, 0.01; 95% confidence interval [CI95], −0.06, 0.11; P = 0.75). Among 51 participants with azithromycin-resistant S. aureus at baseline, 2 had treatment-emergent SCV strains, and among 123 participants without azithromycin resistance, 3 had treatment-emergent SCV strains (difference in proportions, 0.01; CI95, −0.04, 0.11; P = 0.63). Finally, emergence of azithromycin-resistant S. aureus was not associated with treatment-emergent SCV strains; 0 SCV strains emerged among 34 participants with emergence of azithromycin resistance, and 3 SCV strains emerged among 89 participants without azithromycin resistance (difference in proportions, −0.03; CI95, −0.09, 0.07; P = 0.56).

despite treatment-emergent azithromycin-resistant S. aureus, long-term treatment with azithromycin among children and adolescents with CF, most of whom were infected with S. aureus at baseline, was not associated with treatment-emergent SCV strains