A patient on long-term inhaled ipratropium for COPD complains of dry mouth but no tachycardia. The absence of tachycardia with ipratium compared to atropine is best explained by which property?

• A Ipratropium selectively blocks M1 and M3 receptors without affecting cardiac M2 receptors
• B Ipratropium has beta-blocking properties that counteract tachycardia
• C Ipratropium blocks nicotinic ganglionic transmission preventing reflex tachycardia
• D Ipratropium is a quaternary amine with minimal systemic absorption from the airways ✓

Explanation

Ipratropium is a quaternary ammonium compound that, when inhaled, has poor systemic absorption. It acts locally in the airways with limited systemic muscarinic blockade, thus avoiding the cardiac M2 blockade that causes tachycardia with atropine. It is not receptor subtype selective; its therapeutic advantage is pharmacokinetic, not pharmacodynamic.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.