The parasympathetic nervous system plays a major role in regulating airway homeostasis and bronchomotor tone. A variety of noxious stimuli have been demonstrated to increase parasympathetic activity with resultant bronchoconstriction . Vagal nerve fibers that end on muscarinic receptors innervate the larger airway smooth muscles. Cholinergic irritant receptors are also located in the junction between airway mucosal cells. Anticholinergic agents are competitive inhibitors of acetylcholine at the muscarinic receptors and are effective in relieving cholinergic-mediated bronchoconstriction.
Aerosol administration is more bronchoselective and results in fewer systemic adverse effects.
Adverse effects include dry mouth, blurred vision, fever, bradycardia, tachycardia, urinary retention, central nervous system excitement, fever, and mucous plugging caused by its drying effect on secretions. One important benefit observed with ipratropium is its relative lack of effect on mucociliary clearance and ciliary function as compared with atropine. The use of ipratropium avoids accumulation of lower airway secretions. Quaternary compounds are poorly absorbed across mucosal membranes and the blood-brain barrier. Inhalation of ipratropium, therefore, results in local airway effects with minimal systemic effects.