The purpose of this study is to assess the effect of one of five possible study medications used in the treatment of asthma on blood plasma cortisol levels in children aged 5-11 years with persistent asthma.

Inclusion Criteria:

• diagnosis of persistent asthma of ≥6 months duration
• body weight ≥18 kg
• able to discontinue prescribed inhaled corticosteroid (ICS) or ICS combined with long-acting beta-agonist (LABA) before starting study medication
• use of a low or medium daily dose of ICS (either alone or in combination with a LABA) with no use of oral corticosteroids within 3 months prior to Screening Visit
• stable asthma regimen (daily dose unchanged) for ≥2 weeks prior to Screening Visit
• documented positive responsiveness to bronchodilators
• ability to use a peak flow meter correctly and to perform spirometry and PEF measurements
• ability to use an inhaler correctly
• consent/assent for the trial and for pharmacogenetic testing (Note: If unwilling to consent/assent for pharmacogenetic testing, inclusion in the study is still allowed, but no pharmacogenetic samples will be obtained.)

Exclusion Criteria:

• use of a high dose of ICS for ≥30 days within 6 months prior to Screening Visit
• treatment in the emergency room (for a severe asthma exacerbation requiring systemic corticosteroid treatment) or hospitalization for management of airway obstruction within 3 months prior to Screening Visit
• ever required ventilator support for respiratory failure secondary to asthma
• upper or lower respiratory tract infection (viral or bacterial) within 2 weeks prior to Screening Visit
• clinically significant abnormal vital sign
• evidence of oropharyngeal candidiasis
• history of clinically significant renal, hepatic, cardiovascular, metabolic, neurologic, hematologic, ophthalmologic, respiratory, gastrointestinal, cerebrovascular, or other significant medical illness or disorder that may interfere with study participation. Specific examples include but are not limited to insulin-dependent diabetes, active hepatitis, cardiovascular disease including hypertension, or conditions that may interfere with respiratory function such as, bronchiectasis, and cystic fibrosis
• allergy to or intolerance of corticoids, beta-2 agonists, montelukast or any of the inactive ingredients in the medications used in this study
• participation in this same study at another study site
• previous randomization into this study
• participation in another investigational study for the duration of this study
• use of any investigational drug within one month prior to Screening Visit
• previous participation in a study with MF/F or montelukast
• direct association with or family member of one of the investigators or study staff
• sibling of a participant in this study