antimuscarinic

An antimuscarinic is an inhaled bronchodilator that opens the airways by blocking a constriction signal rather than by stimulating a relaxation one. The body normally sends nerve messages, using a chemical called acetylcholine, that tell airway muscle to tighten; this drug intercepts that message so the muscle stays relaxed.

It does this by occupying the muscarinic receptors that acetylcholine would otherwise switch on, which keeps the airway smooth muscle from contracting and also reduces mucus secretion. Short-acting versions act as relievers and are often paired with a short-acting beta-agonist in acute attacks, while long-acting antimuscarinics are taken on a schedule for maintenance, most prominently in COPD.

This class is particularly central in COPD, where it is a first-line maintenance bronchodilator. It is generally well tolerated; because it works on a different pathway from beta-agonists, the two can be combined for additive airway opening. The most common nuisance side effect is a dry mouth, and it should be used cautiously in narrow-angle glaucoma and significant urinary obstruction.