This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Which of the following drug can be given inhalationally for the diagnosis of bronchial hyperactivity in patients who do not have clinically apparent asthma? \nSelect and explain. \nA. Methacholine, B. Bethanechol, C. Pilocarpine, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: DIRECTLY ACTING DRUGS\nThese are the esters of choline and may be natural alkaloids (ACh, muscarine, nicotine,\xa0pilocarpine and arecoline) or synthetic derivatives (methacoline, carbachol and bethanechol).\n\nAcetylcholine is not used clinically, because it is metabolized very quickly by\xa0cholinesterases in the plasma and is not effective even by i.v. route.\nMethacholine has maximum action on myocardium. It can be given inhalationally\xa0for the diagnosis of bronchial hyper-reactivity\xa0in patients who do not have clinically\xa0apparent asthma -\xa0methacholine challenge test.\nBethanechol is mainly used for its action on urinary bladder and has no nicotinic\xa0activity.\nPilocarpine is used in glaucoma, due to its pupillary\xa0constrictor (miotic) action. However, because of its very short duration of action, intraocular tension may increase, even if one or two doses are missed.', 'role': 'assistant'}]