Chronic cough: future directions in chronic cough: mechanisms and antitussives.

Cough is an important defensive reflex of the respiratory tract needed to clear and protect the upper airways; however, it may become exaggerated and interfere with quality of life. Although chronic cough may be successfully treated when associated with the common causes such as asthma and eosinophilic bronchitis, gastrooesophageal reflux disease and post-nasal drip syndrome or rhinosinusitis, increasingly, idiopathic cough or cough with no associated cause is recognised. Chronic cough is often associated with an increased response to tussive agents such as capsaicin, used as an index of the cough reflex. Some airway receptors mediate or influence cough through activation of vagal afferent pathways which converge on brain stem respiratory networks and of supramedullary centres. Plastic changes in intrinsic and synaptic excitability at the brain stem, spinal or ganglionic level may be the mechanism by which the cough reflex is enhanced in chronic cough. Subjective and objective measurements of cough in the clinic are now available but a major unmet need in chronic cough is the availability of effective antitussives. Future directions in chronic cough include the pathophysiological mechanisms of the enhanced cough reflex, and the discovery of effective antitussives that can successfully alleviate chronic cough.