## Pharmacokinetic Distinction Between SABA and LABA ### Onset and Duration Profile **Key Point:** The defining pharmacokinetic difference between SABA and LABA is onset time and duration of action, not receptor selectivity or mechanism. | Feature | SABA | LABA | |---------|------|------| | **Onset** | 5–15 minutes | 30–60 minutes (requires 1–2 weeks for full effect) | | **Duration** | 4–6 hours | 12–24 hours | | **Receptor binding** | Reversible, rapid dissociation | Reversible, slow dissociation (lipophilic depot effect) | | **Clinical use** | Rescue therapy, acute bronchospasm | Maintenance therapy, chronic control | | **Frequency** | PRN or 2–4 times daily | Once or twice daily | ### Structural Basis for Duration Difference **Clinical Pearl:** LABAs (salmeterol, formoterol) are lipophilic molecules that partition into airway tissue, creating a depot effect. This slow release prolongs duration. SABAs (albuterol, terbutaline) are hydrophilic and rapidly absorbed/eliminated. **High-Yield:** LABA monotherapy is contraindicated in asthma without concurrent ICS because LABAs do not reduce airway inflammation — they only provide smooth muscle relaxation. SABAs, being rapid-onset, are ideal for acute relief. ### Clinical Implications 1. **SABA** = rescue inhaler for acute symptoms (blue reliever) 2. **LABA** = maintenance inhaler, always paired with ICS in asthma (combination inhalers like fluticasone–salmeterol) 3. Both are **reversible** agonists — neither irreversibly binds the receptor 4. Both are **beta-2 selective** — not beta-1 selective [cite:KD Tripathi 8e Ch 27]
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