6 years.Montelukast is a cysteinyl leukotriene receptor antagonist used to treat persistent asthma in patients aged 6 years.
The drug has a rapid onset of action. Improvements in lung function and reductions in as-needed 
-agonist usage are apparent within 1 day of initiating montelukast treatment in adults and adolescents (aged 15 years treated with 10 mg/day) or children (aged 6 to 14 years treated with 5 mg/day) with persistent asthma as shown in clinical trials.
In two 12-week, multicentre, randomised, double-blind studies in adults and adolescents aged 15 years with persistent asthma [forced expiratory volume in 1 second (FEV) = 50 to 85% predicted] there was significantly (p 
0.05) greater improvement in FEV, symptom scores, peak expiratory flow (PEF), as-needed -agonist use, peripheral eosinophil counts and health-related quality of life (QOL) in patients treated with montelukast 10 mg/day than in recipients of placebo. Improvements were significantly greater in patients treated with inhaled beclomethasone 400 µg/day than in recipients of montelukast 10 mg/day in 1 of these studies. Nonetheless, 42% of montelukast recipients experienced 11% improvement in FEV, the median improvement in this parameter in beclomethasone-treated patients.
In an 8-week multicentre, randomised, double-blind, study in children aged 6 to 14 years with persistent asthma (FEV 50 to 85% predicted), montelukast 5 mg/day produced significantly greater improvements in FEV, clinic PEF, as-needed -agonist use, peripheral eosinophil counts, asthma exacerbations and QOL scores than placebo.
The combination of montelukast 10 mg/day plus inhaled beclomethasone 200µg twice daily provided significantly better asthma control than inhaled beclomethasone 200µg twice daily in adults with poorly controlled asthma (mean FEV = 72% predicted) despite 4 weeks treatment with inhaled beclomethasone. Patients receiving the combination experienced significant improvements in FEV and morning PEF, significant reductions in daytime symptom scores, as-needed agonist usage and night-time awakenings with asthma, and had significantly lower peripheral blood eosinophil counts after 16 weeks in this multicentre, randomised, double-blind, placebo-controlled study.
Among adults (FEV 70%) treated with montelukast 10 mg/day for 12 weeks, inhaled corticosteroid dosages were titrated downward by 47% (vs 30% in placebo recipients), 40% of patients were tapered off of inhaled corticosteroids (vs 29%), and significantly fewer patients (16 vs 30%) experienced failed corticosteroid rescues in a multicentre, randomised, double-blind study.
During clinical studies, the frequency of adverse events in montelukast-treated adults, adolescents and children was similar to that in placebo recipients.
In conclusion, montelukast is well tolerated and effective in adults and children aged 6 years with persistent asthma including those with exercise-induced bronchoconstriction and/or aspirin sensitivity. Furthermore, montelukast has glucocorticoid sparing properties. Hence, montelukast, as monotherapy in patients with mild persistent asthma, or as an adjunct to inhaled corticosteroids is useful across a broad spectrum of patients with persistent asthma.