Cough is a common symptom of respiratory medicine clinic patients, which has complex etiology and wide-ranging. Cough is usually divided into three categories by time: acute cough, subacute cough and chronic cough. Subacute has a 3~8 weeks course of disease. Its main etiology is postinfectious cough, which is mostly secondary to viral infection.Considering its overexpression in postinfectious patient, Cysteinyl leukotriene (CysLTs) plays a role in gathering eosinophils to respiratory. The level of FENO has a significant correlation with inflammatory airway eosinophils. While CysLTs overexpressed in vivo, the level of FENO may increase. Montelukast, as CysLTs-receptor-1 antagonists， plays a role of controlling airway inflammation and decrease airway high activity by suppressing the biological activity of CysLTs. It is effective in theory to therapy sub-acute cough by Montelukast, to short the course and to relieve cough symptoms as soon as possible. The aim is to research whether FENO can be used as a biomarker to optimized treatment regimen of sub-acute cough.

This project is a prospective, open label, randomized and controlled trial. All subacute cough patients that met the inclusion/exclusion criteria were recruited after signing the consent form. Patients were randomized into biomarker treatment arm and standard treatment arm. Positive or negative biomarker expression was confirmed by assessing fractional concentration of exhaled NO (FENO) level, FENO<25ppb was regarded as negative and FENO≥25ppb was regarded as positive.

Patients in biomarker guided positive treatment arm were given Montelukast Sodium Tablets (p.o., 10mg, q.d.) . Patients in biomarker guided negative treatment arm were given placebo tablets(p.o., 10mg, q.d.). Patients in standard treatment arm were given Montelukast Sodium Tablets (p.o., 10mg, q.d.).All treatment regimens lasted for 10 days and no other antitussive/decongestant or bronchodilators are given to any patients.

Examine results of all patients from all arms were recorded before and after the 10 day treatment. The examine recorded are FENO levels, cough symptom assessment, cough visual assessment, Leicester cough questionnaire, total white blood cell count, neutrophil blood percentage, eosinophil blood percentage. Patient cough free days after treatment and Montelukast Sodium Tablets . Follow up was carried out at the 8th week after first record of symptom and 2 month after treatment.

Inclusion Criteria:

• Cough is the main or only clinical symptom and was persistent for 3-8 weeks
• Chest X-ray reveals no noticeable pathological changes
• ≥18 year old, regardless of gender and ethical background
• Not taking angiotensin-converting enzyme inhibitor
• Patients must join the programme voluntarily and are able to attend examination and follow-up sessions

Exclusion Criteria:

• Patients diagnosed with rhinallergosis, chronic nasosinusitis or bacterial respiratory tract infections
• Patients diagnosed with severe reportorial disease of other severe systemic disease
• Patients who are allergic to any drugs to be tested
• Patients who are non-cooperative during examination sessions or other steps of the trial
• Patients who are not able to or refuse to sign consent