A topic in Clinical Evidence summarizes the evidence on leukotriene receptor antagonists in persistent childhood asthma. One crossover RCT (n=279) on children aged 6 - 14 years previously treated with inhaled corticosteroids for at least 6 weeks, with mean FEV1 78% predicted after 1 month run-in with budesodine 200 ug compared adding oral montelukast 5 mg versus placebo to inhaled budesonide over 4 weeks. There was a slight increase in FEV1 (4.6% vs 3.3%, 95% CI for difference -0.1 to 2.7%, p=0.06). There were fewer asthma exacerbation days with montelukast (12.2% vs 15.9%, p=0.01). No significant difference was found in quality of life measurements, global evaluation or asthma attacks requiring unschedulded medical intervention or treatment with oral corticosteroids.