**Core Concept**
Long-acting beta-2 agonists (LABAs) are bronchodilators that provide sustained bronchodilation by activating beta-2 adrenergic receptors in the lungs, with a duration of action typically exceeding 12 hours. They are used in combination with inhaled corticosteroids for chronic asthma and COPD management.

**Why the Correct Answer is Right**
Salmeterol is a selective, long-acting beta-2 agonist with a half-life of approximately 12–16 hours and a duration of action of up to 12 hours. It acts primarily on beta-2 receptors in the bronchial smooth muscle, leading to sustained relaxation and bronchodilation. Unlike short-acting agonists (e.g., albuterol), salmeterol does not cause rapid tachyphylaxis and is designed for maintenance therapy.

**Why Each Wrong Option is Incorrect**
Option A: Albuterol is a short-acting beta-2 agonist (SABA) with a duration of 3–4 hours; it is not considered long-acting.
Option C: Pirbuterol is also a short-acting beta-2 agonist with a short duration and limited clinical use.
Option D: Orciprenaline is a non-selective beta-agonist with a short duration and is primarily used in emergency settings, not as a long-acting agent.

**Clinical Pearl / High-Yield Fact**
Never use LABAs alone in asthma—always combine with inhaled corticosteroids to reduce exacerbation risk. Salmeterol is a classic example of a LABA and is often paired with fluticasone or budesonide.

✓ Correct Answer: B. Salmeterol