Fractional Concentration of Exhaled NO(FeNO) to Direct The Treatment of Sub-acute Cough：A Prospective, Open Label, Randomized and Placebo-Controlled Trial

Cough is a common symptom that leads patients worldwide to seek medical attention. Subacute cough refers to a cough of 3-8-week duration, and is typically refractory to standard anti-tussive therapy, and a tendency to spontaneous healing was common. Few clinical trials have evaluated therapeutic options for subacute cough. Airway inflammation is an important feature of most of subacute cough, Cysteinyl leukotrienes and FeNO correlates with airway inflammation. Subacute cough often represents a prolonged post-viral response. Cysteinyl leukotrienes increase in virus infection. Airway inflammation induce epithelial cells produce iNOS(inducible nitric oxide synthase,iNOS), and FeNO increase in theory. Montelukast is a cysteinyl leukotriene type 1 receptor antagonist that is reported to improve cough16 and reduces FENO and prevents increases in FENO during reduction of inhaled corticosteroid dose, But A meta-analysis of the effectiveness of LTRA( leukotriene receptor antagonist,LTRA)in treating children with prolonged non-specific cough concluded that, with the lack of evidence, the routine use of LTRA in treating children with non-specific cough cannot be recommended. A randomised, placebo-controlled trial showed montelukast is not an effective treatment for postinfectious cough. Non-specialists or general practitioners of Japan prescribe LTRA very often, which increase. The aim is to research whether FeNO can be used as a biomarker to direct montelukast treatment and optimize treatment regimen of sub-acute cough.