Capsaicin-induced cough in humans.

Area of Science:

• Pharmacology
• Respiratory Medicine
• Clinical Trials

Background:

• Cough is a common symptom with various causes.
• Existing methods for inducing cough in research, like citric acid, have limitations.
• A need exists for reliable and safe cough-inducing agents for human studies.

Purpose of the Study:

• To evaluate capsaicin as a selective cough-inducing agent in healthy human subjects.
• To compare the cough response to capsaicin with that of citric acid.
• To assess the potential of capsaicin in evaluating antitussive (cough-suppressing) agents.

Main Methods:

• Healthy subjects inhaled capsaicin aerosol at varying concentrations.
• Cough response, intensity, and duration were recorded.
• Specific airway conductance was measured.
• Comparisons were made with citric acid challenges.
• The effect of inhaled lidocaine on capsaicin-induced cough was assessed.

Main Results:

• Capsaicin induced immediate, reproducible, and concentration-dependent cough.
• Cough subsided promptly upon cessation of capsaicin inhalation.
• Higher capsaicin concentrations showed a plateau effect on cough.
• No changes in airway conductance or signs of pharyngitis/laryngitis were observed.
• Capsaicin-induced cough was inhibited by lidocaine, while citric acid-induced cough was also suppressed by lidocaine.
• No correlation was found between capsaicin and citric acid cough responses.

Conclusions:

• Capsaicin is a selective and effective cough-inducing agent in humans.
• Its reproducible and dose-dependent nature makes it suitable for cough research.
• Capsaicin offers potential advantages over citric acid for evaluating antitussive drugs.