Current and future prospects for drugs to suppress cough.

Cough is an important defensive reflex of the airway and a common symptom of respiratory disease. After an upper respiratory tract virus infection, cough is transient, but is more persistent with conditions such as asthma, rhinosinusitis, gastroesophageal reflux, chronic obstructive pulmonary disease (COPD) and lung cancer. Treatment directed at these conditions may improve cough, but there remains a need to control cough directly. The most effective antitussives are opioids, such as morphine, codeine or pholcodeine, but they produce side effects including drowsiness, nausea, constipation and physical dependence. Opioids such as k- and d-opioid receptor agonists, non-opioids such as nociceptin, neurokinin and bradykinin receptor antagonists, vanilloid receptor VR(1) antagonists, blockers of sodium-dependent channels, and maxi-K calcium-dependent channel activators of afferent nerves may all represent novel antitussives and this needs to be confirmed in clinical trials.