## Long-Acting Beta-2 Agonists in Asthma **Key Point:** Formoterol is the preferred LABA for ICS/LABA combination therapy in asthma because of its rapid onset of action (within 1–3 minutes) and suitability for both maintenance and reliever therapy. ### Comparison of LABAs | LABA | Onset | Duration | Key Feature | Role in Asthma | | --- | --- | --- | --- | --- | | Formoterol | 1–3 min | 12 hrs | Rapid onset, can be used as reliever | Preferred for ICS/LABA combination | | Salmeterol | 10–20 min | 12 hrs | Slower onset | Maintenance only, not as reliever | | Vilanterol | 4–5 min | 24 hrs | Ultra-long-acting | Used in triple therapy (ICS/LABA/LAMA) | | Bambuterol | 30–60 min | 12–24 hrs | Prodrug of terbutaline | Rarely used in modern asthma management | **High-Yield:** Formoterol's rapid onset allows it to be used as both a maintenance agent AND a reliever in the "budesonide–formoterol as needed" regimen (MART — Maintenance and Reliever Therapy), which is now endorsed by GINA guidelines for mild-to-moderate persistent asthma. **Clinical Pearl:** Salmeterol, despite being a LABA, should NEVER be used as a reliever because of its slow onset; patients may incorrectly assume it is working and delay use of a true rescue bronchodilator, risking severe exacerbation. **Mnemonic:** FORM = **F**ast **O**nset **R**apid **M**echanism (Formoterol) — remember it for rapid-onset LABA. 
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