Ipratropium bromide, unlike atropine, does not cross the blood-brain barrier primarily because it:

• A Is an ester that is rapidly hydrolysed in plasma
• B Is a quaternary ammonium compound with low lipid solubility ✓
• C Binds exclusively to M3 receptors on bronchial smooth muscle
• D Undergoes first-pass metabolism by lung amine oxidases

Explanation

Ipratropium is a quaternary ammonium derivative of atropine; the permanent positive charge greatly reduces its lipid solubility, preventing significant CNS penetration. Atropine is a tertiary amine and crosses the BBB readily. Ipratropium does not have receptor subtype exclusivity, nor is it hydrolysed in plasma to any clinically relevant degree.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.