Which of the following drug can be given inhalationally for the diagnosis of bronchial hyperactivity in patients who do not have clinically apparent asthma?

DIRECTLY ACTING DRUGS These are the esters of choline and may be natural alkaloids (ACh, muscarine, nicotine, pilocarpine and arecoline) or synthetic derivatives (methacoline, carbachol and bethanechol). Acetylcholine is not used clinically, because it is metabolized very quickly by cholinesterases in the plasma and is not effective even by i.v. route. Methacholine has maximum action on myocardium. It can be given inhalationally for the diagnosis of bronchial hyper-reactivity in patients who do not have clinically apparent asthma - methacholine challenge test. Bethanechol is mainly used for its action on urinary bladder and has no nicotinic activity. Pilocarpine is used in glaucoma, due to its pupillary constrictor (miotic) action. However, because of its very short duration of action, intraocular tension may increase, even if one or two doses are missed.