Which anticholinesterase drug would be most useful in treating poisoning with atropine derived from Atropa belladonna?

Physostigmine is the most suitable anticholinesterase drug for treating poisoning with atropine, which is a muscarinic antagonist derived from Atropa belladonna. Atropine works by blocking the action of acetylcholine at muscarinic receptors, leading to symptoms such as dry mouth, increased heart rate, dilated pupils, and impaired sweating.

Physostigmine functions by inhibiting the enzyme acetylcholinesterase, which breaks down acetylcholine in the synaptic cleft. This inhibition increases the levels of acetylcholine, allowing it to compete with atropine for binding to muscarinic receptors. Consequently, physostigmine can effectively counteract the effects of atropine, reversing the toxic symptoms by enhancing cholinergic receptor activity.

Other options, such as malathion, are organophosphate compounds that also inhibit acetylcholinesterase but are not specific antidotes for atropine poisoning and can exacerbate cholinergic symptoms rather than alleviate them. Muscarinic antagonists would further aggravate the situation by blocking additional acetylcholine, and nicotinic antagonists primarily affect neuromuscular junctions, which are not relevant in the context of atropine poisoning affecting the central nervous system