Name a cholinergic agent that can be used as an antidote for poisoning from anticholinergic agents.

Physostigmine is a reversible acetylcholinesterase inhibitor that increases the concentration of acetylcholine in the synaptic cleft. In cases of anticholinergic poisoning, which can result from overdose of drugs that block acetylcholine receptors, physostigmine can help restore balance by promoting the action of acetylcholine. It enhances cholinergic transmission, thereby counteracting the effects of anticholinergic agents, such as confusion, agitation, and delirium.

While atropine, a commonly known anticholinergic agent, is used to treat bradycardia and reduce secretions, it would not serve as an antidote for anticholinergic poisoning since it has similar mechanisms of action as those being targeted in anticholinergic toxicity. Pyridostigmine, primarily used in the treatment of myasthenia gravis, and donepezil, used for Alzheimer's disease, are also in this category of medications that act more specifically on skeletal muscle and cognitive function, respectively, rather than effectively reversing symptoms of anticholinergic toxicity. Thus, physostigmine stands out as the appropriate antidote for this type of poisoning.