Which of the following beta-2 agonists is a selective short-acting agent with rapid onset and is commonly used for acute bronchospasm relief?

Explanation

## Short-Acting Beta-2 Agonists (SABAs) **Key Point:** Salbutamol (albuterol in the US) is the prototypical selective β₂-adrenergic agonist used for acute relief of bronchospasm. ### Mechanism of Action Salbutamol binds to β₂-adrenergic receptors on airway smooth muscle, activating adenylyl cyclase via G-protein coupling, increasing intracellular cAMP and causing bronchial smooth muscle relaxation. ### Pharmacokinetic Profile - **Onset:** 5–15 minutes (inhaled) - **Peak effect:** 30–60 minutes - **Duration:** 4–6 hours - **Route:** Inhaled (MDI, nebulizer), oral, IV - **Selectivity:** β₂ > β₁ (at therapeutic doses) ### Clinical Use - First-line agent for acute bronchospasm and asthma exacerbations - Rescue inhaler in all asthma patients - Useful in COPD acute episodes **High-Yield:** Salbutamol is the gold standard SABA and is universally available; it is the first-line reliever medication in all asthma guidelines. ### Comparison with Other Beta-2 Agonists | Agent | Type | Onset | Duration | Clinical Use | |-------|------|-------|----------|---------------| | Salbutamol | SABA | 5–15 min | 4–6 hrs | Acute relief, rescue | | Salmeterol | LABA | 10–20 min | 12 hrs | Maintenance, prevention | | Formoterol | LABA | 5–10 min | 12 hrs | Maintenance, can be used acutely | | Vilanterol | LABA | Slow | 24 hrs | Once-daily maintenance | **Clinical Pearl:** Salbutamol's rapid onset makes it ideal for acute symptom relief, whereas LABAs (salmeterol, formoterol, vilanterol) are reserved for maintenance therapy and should never be used as monotherapy in asthma due to increased mortality risk.