Ipratropium bromide produces bronchodilation in COPD without causing the systemic anticholinergic effects seen with atropine, such as urinary retention and tachycardia. The property responsible for this safety profile is:

• A It is a tertiary amine that is rapidly metabolised by plasma esterases
• B It undergoes extensive first-pass metabolism in the liver
• C It selectively blocks M3 receptors while sparing M1 and M2 receptors
• D It is a quaternary ammonium derivative with poor systemic absorption across biological membranes ✓

Explanation

Ipratropium is a quaternary ammonium derivative of atropine. Its permanently charged nitrogen prevents significant absorption from the airway mucosa into the circulation, so it acts topically with negligible systemic anticholinergic effects. It is not receptor subtype selective, blocking all muscarinic subtypes locally, and its safety is unrelated to esterase metabolism or first-pass clearance since it is given by inhalation.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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