Ipratropium bromide produces effective bronchodilation in COPD with negligible systemic anticholinergic side effects such as urinary retention or tachycardia. Which property of the molecule best explains this safety profile?
- A It is a quaternary ammonium derivative with poor absorption across biological membranes ✓
- B It is a partial agonist at muscarinic receptors
- C It is rapidly metabolised by plasma cholinesterase before reaching the circulation
- D It selectively antagonises M2 receptors in the airways only
Correct answer: A. It is a quaternary ammonium derivative with poor absorption across biological membranes
Explanation
Ipratropium carries a permanent positive charge as a quaternary ammonium compound, so it is poorly absorbed from the airway mucosa into the systemic circulation and does not cross the blood-brain barrier. This limits effects to local muscarinic blockade. It is a competitive antagonist, not an agonist, and it blocks M3 receptors chiefly, so options B, C and D are incorrect statements.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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