Which agent acts exclusively peripherally as a reversible anticholinesterase?

Which agent acts exclusively peripherally as a reversible anticholinesterase?

• A. Neostigmine
• B. Physostigmine
• C. Organophosphates
• D. Succinylcholine

Answer: (A)

The main idea is that some acetylcholinesterase inhibitors act only in the periphery and do so reversibly. Neostigmine is a quaternary ammonium compound, so it doesn’t cross the blood–brain barrier well and mainly affects peripheral cholinergic sites like the neuromuscular junction and autonomic synapses. It reversibly inhibits acetylcholinesterase, so acetylcholine levels rise temporarily. This makes it useful for reversing nondepolarizing neuromuscular blockers after surgery and for treating myasthenia gravis, where more acetylcholine is needed at the NMJ to overcome receptor loss. In contrast, physostigmine can enter the CNS because it’s a tertiary amine, so it has central as well as peripheral effects. Organophosphates inhibit acetylcholinesterase irreversibly, leading to prolonged cholinergic effects and toxicity. Succinylcholine isn’t an acetylcholinesterase inhibitor at all; it’s a depolarizing neuromuscular blocker that activates nicotinic receptors.

The main idea is that some acetylcholinesterase inhibitors act only in the periphery and do so reversibly. Neostigmine is a quaternary ammonium compound, so it doesn’t cross the blood–brain barrier well and mainly affects peripheral cholinergic sites like the neuromuscular junction and autonomic synapses. It reversibly inhibits acetylcholinesterase, so acetylcholine levels rise temporarily. This makes it useful for reversing nondepolarizing neuromuscular blockers after surgery and for treating myasthenia gravis, where more acetylcholine is needed at the NMJ to overcome receptor loss.

In contrast, physostigmine can enter the CNS because it’s a tertiary amine, so it has central as well as peripheral effects. Organophosphates inhibit acetylcholinesterase irreversibly, leading to prolonged cholinergic effects and toxicity. Succinylcholine isn’t an acetylcholinesterase inhibitor at all; it’s a depolarizing neuromuscular blocker that activates nicotinic receptors.