Longest acting β–agonist is :
**Core Concept**
The question is testing the knowledge of long-acting beta-agonists (LABAs), a class of bronchodilators used in the management of asthma and chronic obstructive pulmonary disease (COPD). LABAs work by activating beta-2 adrenergic receptors in the lungs, causing bronchodilation.
**Why the Correct Answer is Right**
The longest acting β–agonist is Salmeterol, which has a duration of action of approximately 12 hours. Salmeterol is a selective beta-2 adrenergic receptor agonist that binds to the receptor with high affinity, leading to prolonged bronchodilation. Its long duration of action is due to its slow onset of action and slow dissociation from the receptor.
**Why Each Wrong Option is Incorrect**
* **Option A:** Terbutaline is a short-acting beta-agonist (SABA) with a duration of action of approximately 4-6 hours, making it an incorrect choice.
* **Option B:** Formoterol is a long-acting beta-agonist (LABA) but has a shorter duration of action compared to Salmeterol, typically around 12 hours but can be less in some cases.
* **Option D:** Albuterol (also known as Salbutamol) is a SABA, similar to Terbutaline, with a short duration of action.
**Clinical Pearl / High-Yield Fact**
When prescribing LABAs, it's essential to remember that they should not be used as monotherapy in asthma, but rather in combination with inhaled corticosteroids (ICS) to reduce the risk of exacerbations and improve lung function.
**Correct Answer: C. Salmeterol.**