ATP and Capsaicin Cough Provocation Test in Chronic Cough and Bronchiectasis

Adenosine Triphosphate and Capsaicin Cough Provocation Test for Identifing Patients With Chronic Cough Who Have Differential Responses to Purinergic Receptor Antagonists: a Randomized, Cross-over, Single-blind Trial

This is a randomized, cross-over, single-blind trial. Eligible patients will be randomly assigned to undergo either capsaicin or adenosine triphosphate (ATP) cough provocation test, followed by a washout period of 2 to 14 days. Participants will be crossed-over to undergo another cough provocation test. Patient would be under observation in the out-patient clinics for ~2 hours following the cough provocation tests in case of severe adverse events.

This is a randomized, cross-over, single-blind trial. After verification of the entry criteria, eligible patients will be, based on the randomization codes, randomly assigned to undergo either capsaicin or ATP cough provocation test (the participants will inhale capasaicin or ATP incremental concentration to induce cough, meanwhile the number of coughs and adverse events will be recorded in each concentration during the first 30 seconds), followed by a washout period of 2 to 14 days (no major changes in the use of concomitant medications are allowed,especially the medcines which are not allowed before test ). Participants will be crossed-over to undergo another cough provocation test. Patient would be under observation in the out-patient clinics for ~2 hours following the cough provocation tests in case of severe adverse events. Twenty four hours after each test, a follow-up telephone visit will be scheduled for all patients to record any response which may be related to the test.

Inclusion Criteria:

• Out-patients of either gender, ex- or never-smokers, aged between 18 and 60 years
• Cough symptoms lasting for more than 8 weeks
• Remaining free of acute upper respiratory tract infection for at least 4 weeks
• Agreed to participate in the trial and signed informed consent.

Exclusion Criteria:

• Patients with serious systemic diseases (such as malignant tumors), bullae, severe uncontrolled asthma, and a history of major hemoptysis
• Systemic antibiotic use (except for maintenance low-dose macrolides) within 4 weeks
• Pregnancy or lactation
• Any known history of sensitivity to ATP or capsaicin
• Poor understanding of the test procedure
• Diagnosed with cough variant asthma or Eosinophilic bronchitis