A repeat-dose open label randomized incomplete block design in pediatric subjects with asthma, ages 4-11 years, to compare systemic exposure and pharmacodynamics of fluticasone propionate and salmeterol following ADVAIR HFA 45/21mcg(2 inhalations), ADVAIR HFA 45/21mcg(2 inhalations) with Aerochamber Plus Spacer and ADVAIR DISKUS 100/50 twice daily
