Final answer:
Physostigmine (Antilirum) is a parasympathomimetic drug that inhibits acetylcholinesterase, thereby enhancing acetylcholine activity at muscarinic receptors. Its effect is short to medium-acting and it is absorbed in the gastrointestinal tract. It serves as an antidote to anticholinergic drugs like atropine by stimulating muscarinic receptors.
Step-by-step explanation:
Physostigmine (Antilirum) acts as a parasympathomimetic drug. It works by inhibiting acetylcholinesterase, an enzyme responsible for breaking down the neurotransmitter acetylcholine. This inhibition increases acetylcholine levels at synapses, thus enhancing cholinergic transmission.
Physostigmine stimulates muscarinic acetylcholine receptors which are metabotropic receptors. By augmenting acetylcholine activity, its effect mimics parasympathetic postganglionic impulses, increasing parasympathetic outflows to various organs. The duration of action for Physostigmine is generally considered to be short to medium. It is absorbed in various tissues but predominantly in the gastrointestinal tract during oral administration. The increased absorption in undesired tissues can lead to an array of side effects, such as muscarinic effects in the heart or gastrointestinal system.
As for an antidote to atropine poisoning, which is an anticholinergic drug, a muscarinic agonist such as Physostigmine would be the correct choice (answer to question 24).