Antibiotic Treatment Of Staphylococcus Aureus In Stable People With CF

This is a randomized, double-blinded study that aims to assess the effect of an oral antibiotic called Cephalexin (150 mg/kg/day) compared to placebo in clinically stable children with cystic fibrosis who have grown a bacteria called MSSA (methicillin-susceptible Staphylococcus aureus) over the course of 2 weeks. A sensitive technique called MBW (multiple breath washout) will be used to look at how well the participants lungs are functioning during the study and to see if the antibiotic improves function. The primary outcome of the study will be the relative change in the MBW measurement (LCI2.5) between day 0 and day 14 of study treatment.