Cough is an adverse effect that may hinder the delivery of drugs into
the lungs. Chemical or mechanical stimulants activate the transient
receptor potential in some airway afferent nerves (C or A fibres) to
trigger cough. Types of inhaler device and drug, dose, excipients,
formulation characteristics including pH, tonicity, aerosol output and
particle size may trigger cough by stimulating the cough receptors.
Release of inflammatory mediators may increase the sensitivity of the
cough receptors to stimulants. The cough-provoking effect of aerosols is
enhanced by bronchoconstriction in diseased airways and reduces drug
deposition in the target pulmonary regions. In this article, we review
the factors by which inhalation products may cause cough.