Which cholinesterase inhibitor is similar to neostigmine?

• A. Demecarium
• B. Physostigmine
• C. Neostigmine
• D. Pyridostigmine

Answer: (B)

Cholinesterase inhibitors that are carbamates work by reversibly inhibiting acetylcholinesterase through carbamylation of the enzyme, which raises acetylcholine levels at both nicotinic (neuromuscular) and muscarinic sites.

Physostigmine fits this pattern because it is a carbamate acetylcholinesterase inhibitor with a reversible mechanism similar to neostigmine. Both increase acetylcholine at the neuromuscular junction, helping restore function in conditions like myasthenia gravis and enabling reversal of certain blocks, though physostigmine is the tertiary-amine form that can cross the blood-brain barrier and has central effects, unlike neostigmine which is quaternary and largely excludes the CNS. The other options are either longer-acting or used in different contexts (such as ocular glaucoma) or have different central/peripheral profiles, making physostigmine the closest pharmacologic relative to neostigmine in mechanism and class.