antimuscarinic bronchodilator
An antimuscarinic bronchodilator opens the airways by cutting the nerve signal that keeps them slightly squeezed. The lungs receive a constant 'tighten' message through the parasympathetic nerves; block that message and the airway muscle relaxes.
These inhaled anticholinergics — ipratropium (short-acting) and tiotropium, glycopyrronium and umeclidinium (long-acting) — block muscarinic M3 receptors on airway smooth muscle and mucus glands. Acetylcholine normally acts there to constrict airways and increase secretions, so blocking it produces bronchodilation and drier secretions. They are central to maintenance treatment of COPD and are also used as add-on therapy in asthma, often combined with a beta-2 agonist for greater effect.
Delivered by inhaler, very little is absorbed, so the classic anticholinergic side effects (dry mouth, blurred vision, urinary difficulty, constipation) are usually mild, though caution is advised in glaucoma and bladder outflow problems. They act more slowly than short-acting beta-2 agonists, so they are not the first reach in a sudden severe attack, where a fast beta-2 agonist takes the lead.
A patient with COPD inhales tiotropium once daily as long-acting maintenance to keep the airways open.
Tiotropium blocks airway muscarinic M3 receptors for sustained bronchodilation in COPD.
Because they act more slowly than beta-2 agonists, antimuscarinic bronchodilators are mainly for maintenance and add-on use rather than first-line rescue in a sudden attack.