Efficacy of Fluticasone Propionate Associated With Salmeterol Using Inhalation Chamber Versus Placebo to Improve the Respiratory Function in Children Over Six Years of Age Who Underwent Allogeneic Hematopoietic Stem Cell Transplantation With a Decline of FEV1 ≥10% From Pre Transplantation

"For children between 6 to 11 years (\< 12 years): 50 μg inhaled fluticasone propionate and 25 μg salmeterol (SERETIDE® 50/25) :two puffs twice a day from randomisation during 6 months using inhalation chamber~\- For children between 12 to 17 years (\> or = 12 years) : 125 μg inhaled fluticasone propionate and 25 μg salmeterol (SERETIDE® 125/25): two puffs twice a day from randomisation during 6 months using inhalation chamber"

For children between 6 to 11 years (\< 12 years): placebo of SERETIDE® 50/25 :two puffs twice a day from randomisation during 6 months using inhalation chamber For children between 12 to 17 years (\> or = 12 years) : placebo of SERETIDE® 125/25: two puffs twice a day from randomisation during 6 months using inhalation chamber