Which statement about physostigmine is true?

Which statement about physostigmine is true?

• A. It is a reversible anticholinesterase
• B. It acts exclusively peripherally
• C. It cannot cross the blood-brain barrier
• D. It is not used for xerostomia

Answer: (A)

Physostigmine is a reversible acetylcholinesterase inhibitor. As a carbamate, it binds AChE temporarily and is hydrolyzed, so the enzyme activity eventually returns and the effect wears off. By blocking AChE, it raises acetylcholine levels at synapses, enhancing transmission at both muscarinic and nicotinic receptors in the peripheral and central nervous systems. Its lipophilic, tertiary amine structure lets it cross the blood–brain barrier, giving central cholinergic effects that are useful for reversing anticholinergic toxicity. This contrasts with statements that it acts only peripherally or that it cannot enter the CNS. Because its action is reversible, it is not like irreversible organophosphate poisons that form long-lasting covalent bonds with AChE. In practice, physostigmine is used to counteract anticholinergic toxicity and for some ocular indications; it is not a routine treatment for xerostomia, which reflects the fact that sialogogues like pilocarpine are typically preferred for stimulating saliva.

Physostigmine is a reversible acetylcholinesterase inhibitor. As a carbamate, it binds AChE temporarily and is hydrolyzed, so the enzyme activity eventually returns and the effect wears off. By blocking AChE, it raises acetylcholine levels at synapses, enhancing transmission at both muscarinic and nicotinic receptors in the peripheral and central nervous systems. Its lipophilic, tertiary amine structure lets it cross the blood–brain barrier, giving central cholinergic effects that are useful for reversing anticholinergic toxicity. This contrasts with statements that it acts only peripherally or that it cannot enter the CNS. Because its action is reversible, it is not like irreversible organophosphate poisons that form long-lasting covalent bonds with AChE. In practice, physostigmine is used to counteract anticholinergic toxicity and for some ocular indications; it is not a routine treatment for xerostomia, which reflects the fact that sialogogues like pilocarpine are typically preferred for stimulating saliva.