## Long-Acting Beta-2 Agonists (LABAs) **Key Point:** Salmeterol is a long-acting beta-2 agonist (LABA) with a duration of action of 12 hours, making it ideal for maintenance therapy in COPD and asthma. ### Mechanism of Prolonged Action Salmeterol has a long lipophilic side chain that allows: 1. Depot formation in airway tissues 2. Gradual release from the depot over 12 hours 3. Sustained beta-2 receptor stimulation ### Comparison of Beta-2 Agonists | Agent | Type | Duration | Clinical Use | |-------|------|----------|---------------| | Salbutamol | Short-acting (SABA) | 4–6 hours | Acute relief, rescue | | Terbutaline | Short-acting (SABA) | 4–6 hours | Acute relief | | Salmeterol | Long-acting (LABA) | 12 hours | Maintenance therapy | | Isoproterenol | Short-acting (SABA) | 1–3 hours | Rarely used; non-selective | **High-Yield:** LABAs like salmeterol should NEVER be used as monotherapy in asthma; they must be combined with an inhaled corticosteroid (ICS) due to increased risk of asthma-related deaths when used alone. **Clinical Pearl:** Salmeterol takes 10–20 minutes to reach peak effect, so it is NOT suitable for acute relief; salbutamol is the rescue agent of choice. **Mnemonic:** LABAs = **L**ong-**A**cting **B**eta-2 **A**gonists — think "maintenance" (salmeterol, formoterol, vilanterol).
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