bronchodilator

During an asthma attack, the muscle wrapped around the airways tightens like a fist, narrowing the tubes you breathe through. A bronchodilator tells that muscle to relax and open up, so air can move freely again. It is a rescue from breathlessness rather than a cure for the underlying inflammation.

The main class are beta-2 agonists: they activate the beta-2 adrenergic receptor, a G-protein-coupled receptor on airway smooth muscle, triggering a signal that relaxes the muscle. They are essentially the mirror image of a beta-blocker, switching the same kind of receptor on rather than off.

Chemically these drugs descend from adrenaline itself, keeping a catechol-like or modified aromatic head and a basic amine, then tuning the structure for beta-2 selectivity and duration. Short-acting agents such as salbutamol act within minutes; long-acting ones such as salmeterol and formoterol are anchored to last many hours. A separate group, the muscarinic antagonists (such as tiotropium), relaxes airways by a different receptor, and theophylline acts on intracellular enzymes.

An honest caveat: because perfect beta-2 selectivity is impossible, high doses can spill over onto beta-1 receptors and cause a racing heart or tremor, and a bronchodilator relieves symptoms without treating the inflammation that drives chronic asthma.