PULM Module 1 Infographic — Bronchodilators

Bronchodilators: Beta-2 Agonists and Anticholinergics

Airway signaling, drug classes, and clinical positioning in asthma and COPD

Airway Smooth Muscle Signaling

Bronchoconstriction

Gq-coupled receptors
(M3 muscarinic, CysLT1, H1)

↓ Phospholipase C → IP3

↓ Calcium release → MLCK activated

↓ Myosin phosphorylation → Contraction

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Bronchodilation

Gs-coupled beta-2 receptors
(epinephrine, beta-2 agonists)

↓ Adenylyl cyclase → cyclic AMP

↓ Protein kinase A → MLCK inhibited

↓ Myosin dephosphorylation → Relaxation

Beta-2 Agonist Comparison

	Albuterol	Salmeterol	Formoterol	Indacaterol
Class	SABA	LABA	LABA	Ultra-LABA
Onset	5–15 min	10–20 min	1–3 min	<5 min
Duration	4–6 h	12 h	12 h	24 h
Agonist type	Full	Partial	Full	Full
Rescue use?	Yes	No	Yes (SMART)	No

Anticholinergic Bronchodilators

SAMA

Ipratropium

Non-selective: M1, M2, M3
Onset 15–30 min | Duration 4–8 h
Add-on in acute severe asthma
Minimal systemic absorption (quaternary N)

LAMA

Tiotropium

Kinetic M3 selectivity (slow M3 dissociation)
Once-daily | 24 h bronchodilation
First-line COPD maintenance
Contraindicated: angle-closure glaucoma

Safety and Clinical Positioning

LABA Safety Rule in Asthma

LABA monotherapy is absolutely contraindicated in asthma. The SMART trial demonstrated excess asthma mortality with salmeterol without inhaled corticosteroids. In asthma, LABAs are prescribed only as fixed-dose ICS/LABA combinations. LABA monotherapy is appropriate in COPD.