respiratory:beta2_agonists
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β2-Agonists (SABA / LABA)
respiratory bronchodilator beta2_agonist
β2-agonists relax bronchial smooth muscle and are the primary bronchodilators used in obstructive lung disease.
They do NOT treat inflammation — they only open the airway.
SABA = rescue (fast relief)
LABA = maintenance (prevention)
Mechanism of Action
β2 receptor activation → ↑ cAMP → smooth muscle relaxation → bronchodilation
Additional effects:
- ↓ mast cell mediator release
- ↑ mucociliary clearance
- ↓ airway resistance
Onset and duration determine clinical use.
Drug Classification
| Class | Onset | Duration | Clinical Role |
|---|---|---|---|
| SABA | Minutes | 3–6 hr | Rescue inhaler |
| LABA | 5–20 min | 12–24 hr | Controller therapy |
Short-Acting β2 Agonists (Rescue)
Rapid symptom relief — used PRN for bronchospasm
Clinical Uses:
- Acute asthma symptoms
- Exercise-induced bronchospasm
- COPD rescue therapy
Long-Acting β2 Agonists (Maintenance)
Prevent bronchospasm — NOT rescue therapy
Clinical Uses:
- Asthma maintenance (must be combined with ICS)
- COPD maintenance therapy
High-Yield Safety Rule
LABA monotherapy in asthma increases mortality Always combine with inhaled corticosteroid
Adverse Effects
| Effect | Mechanism |
|---|---|
| Tremor | Skeletal muscle β2 stimulation |
| Tachycardia | β1 spillover at high dose |
| Hypokalemia | Cellular potassium shift |
| Hyperglycemia | Hepatic glycogenolysis |
| Anxiety | Adrenergic stimulation |
Clinical Pearls
- Frequent SABA use = uncontrolled asthma
- Formoterol acts fast → used in SMART therapy
- LABA improves nighttime symptoms
- COPD relies heavily on bronchodilation vs inflammation control
Think: β2 agonists open the airway — steroids calm the airway
respiratory/beta2_agonists.1771167374.txt.gz · Last modified: by andrew2393cns