Anticholinergics in Respiratory Care

Inhaled anticholinergics are muscarinic receptor antagonists. They prevent acetylcholine from stimulating airway muscarinic receptors, especially M3 receptors on bronchial smooth muscle and secretory glands. The result is less vagally mediated bronchoconstriction, less mucus secretion, and bronchodilation. These drugs do not stimulate beta-2 receptors. That distinction matters clinically: a short-acting beta-2 agonist (SABA) rapidly relaxes airway smooth muscle through beta-2 stimulation, whereas an anticholinergic removes part of the cholinergic signal that keeps the airway narrowed. The mechanisms complement each other, which is why salbutamol and ipratropium may be used together during an acute COPD exacerbation or severe asthma episode. Ipratropium is a short-acting muscarinic antagonist (SAMA). Its effect begins within minutes and lasts several hours. Long-acting muscarinic antagonists (LAMAs), such as tiotropium, aclidinium, glycopyrronium, and umeclidinium, remain bound to M3 receptors longer and provide sustained bronchodilation for 12 to 24 hours. They are maintenance medicines, not rapid symptom relievers.