Both salmeterol and formoterol are long-acting beta-2 agonists combined with inhaled corticosteroids in asthma. Which statement correctly distinguishes them?
- A Formoterol has slower onset because of greater lipophilicity
- B Salmeterol is short acting while formoterol lasts 24 hours
- C Salmeterol has slower onset because its lipophilic tail anchors it in the membrane away from the receptor ✓
- D Formoterol is a partial agonist whereas salmeterol is a full agonist
Correct answer: C. Salmeterol has slower onset because its lipophilic tail anchors it in the membrane away from the receptor
Explanation
Salmeterol's long lipophilic side chain anchors it within the plasma membrane adjacent to the receptor, producing a persistent 'exo-site' effect but slow access to the active site, hence delayed onset of about 20 to 30 minutes. Formoterol is moderately lipophilic with faster receptor association, giving near-immediate onset comparable to salbutamol. Both are full agonists with durations around 12 hours.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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