Table 1.

Summary of possible mechanisms by which antihistamines could suppress cough due to UACS

Mechanism	Description
Peripheral direct	Histamine receptors on sensory afferents may promote the production of cough
Peripheral indirect	Nasal mucus secretion induced by histamine receptors promotes cough by a mechanical action on pharyngeal or laryngeal mechanoreceptors that elicit cough Nasal mucus secretion induced by cholinergic mechanisms produces cough by a mechanical action on pharyngeal or laryngeal mechanoreceptors that elicit cough
Central direct	Histamine H1 receptors in the central nervous system may directly promote the production of cough. Access to these receptors would require a centrally penetrant H1 antihistamine Centrally penetrant H1 antihistamines may bind to nonhistaminergic receptors in the central nervous system that control cough excitability
Central indirect	Histamine H1 receptors in the central nervous system may regulate nasal mucus secretion. Access to these receptors would require a centrally penetrant H1 antihistamine Centrally penetrant antihistamines may bind to nonhistaminergic receptors that regulate mucus secretion Centrally penetrant antihistamines induce sedation that could result in a reduction in cough excitability