Evidence Level B
Randomized controlled trials (RCTs) of <200 participants, methodologically flawed RCTs of >200 participants, methodologically flawed systematic reviews (SRs) or good quality observational (cohort) studies.
Symptom severity: there is medium-quality evidence that leukotriene antagonists plus inhaled corticosteroids are no more effective than increasing inhaled corticosteroids at decreasing daytime symptoms and days with asthma exacerbations or nocturnal wakening, or at improving peak expiratory flow rate (PEFR) in people with mild to moderate persistent asthma.
More info from BMJ Clinical Evidence
