Which statement about physostigmine is true?

Which statement about physostigmine is true?

• A. It does not cross the blood-brain barrier.
• B. It crosses the blood-brain barrier.
• C. It is not an acetylcholinesterase inhibitor.
• D. It is preferred over pyridostigmine due to longer duration.

Answer: (B)

Physostigmine can cross the blood-brain barrier because it is a tertiary amine acetylcholinesterase inhibitor, making it lipid-soluble. This CNS penetration is what lets it counteract central symptoms of anticholinergic toxicity (like delirium and agitation) in addition to its peripheral effects. In contrast, pyridostigmine is a quaternary ammonium compound that does not cross into the CNS and generally has a longer peripheral duration of action. Therefore, the statement that it crosses the blood-brain barrier is true.

Physostigmine can cross the blood-brain barrier because it is a tertiary amine acetylcholinesterase inhibitor, making it lipid-soluble. This CNS penetration is what lets it counteract central symptoms of anticholinergic toxicity (like delirium and agitation) in addition to its peripheral effects. In contrast, pyridostigmine is a quaternary ammonium compound that does not cross into the CNS and generally has a longer peripheral duration of action. Therefore, the statement that it crosses the blood-brain barrier is true.