A 60-year-old man with Alzheimer's disease is prescribed rivastigmine. The drug inhibits acetylcholinesterase and butyrylcholinesterase. Which property best explains the PREFERENTIAL central action of rivastigmine compared to neostigmine?

• A Rivastigmine is a quaternary ammonium compound
• B Rivastigmine undergoes extensive first-pass hepatic metabolism
• C Rivastigmine has a longer plasma half-life than neostigmine
• D Rivastigmine is a lipid-soluble tertiary amine that crosses the blood-brain barrier ✓

Explanation

Rivastigmine is a lipophilic tertiary amine that readily crosses the blood-brain barrier, enabling central cholinesterase inhibition for Alzheimer's therapy. Neostigmine is a quaternary ammonium compound with a permanent positive charge that cannot cross the blood-brain barrier, restricting it to peripheral actions. This physicochemical difference, not half-life, underlies the selectivity for central versus peripheral effects.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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