What is Which of the following is a parasympatholytic agent? and explain in detail?
ANSWER: (A) AtropineREF: KDT 6th edp. 103The question is simply based upon the classification of cholinergic drugsSUBTYPES AND CHARACTERISTICS OF CHOLINOCEPTORSReceptorTypeOther NamesLocationStructural FeaturesPost receptor MechanismMlMiaNervesSeven transmembrane segments G protein linkedIP3, DAG cascadeM2M2a, cardiac M2Heart, nerves smooth muscleSeven transmembrane segments, G protein linkedInhibition of cAMP production, activation of K+ channelsM3M2bGlands, smooth muscle, endotheliumSeven transmembrane segments, G protein linkedIP3, DAG cascadeNMMuscle type,end platereceptorSkeletal muscle neuromuscular junctionPentamerNa+, K+ depolarizing ion channelNNNeuronal type,ganglionreceptorPostganglionic cell body, dendritesAlpha and beta subunits onlyNa+, K+ depolarizing ion channelGenesCHOLINERGIC DRUGS:Direct-acting: These act by stimulating the nicotinic or muscarinic receptors.A. Choline estersAcetylcholine (all acetylcholine receptors)Bethanechol (M3 receptors)Carbachol (all muscarinic receptors and some nicotinic receptors)Methacholine (all muscarinic receptors)B. Plant alkaloidsArecolineNicotineMuscarinePilocarpine (M3 receptors)II. Indirect-acting: Indirect acting parasympathomimetic drugs may be reversible cholinesterase inhibitors, irreversible cholinesterase inhibitors or drugs that promote ACh release or anti-adrenergics. The latter inhibits the antagonistic system, the sympathetic nervous system.Reversible cholinesterase inhibitorsDonepezilEdrophoniumNeostigminePhysostigminePyridostigmineRivastigmineTacrineCaffeineIrreversible cholinesterase inhibitorsEchothiophateIsoflurophateMalathionParasympathetolytics or anti cholinergics and their uses:Natural alkaloids : atropine , scopolamineCentral anticholinergics : trihexyphenidyl, benztropine and biperidin are used for drug induced parkinsonismAtropine , homartropine , cyclopetntolate and tropicamide are used as mydriatic and cycloplegicsHyoscine induces twilight sleep and transdermal patch of scopolamine is used for motion sicknessAtropine is also used for treatment of AV block and digitalis poisoning, OPC poisoning, cobra bite, myasthenia, early mushroom poisoning.Glycopyrrolate is used as preanesthetic medicationIpratropium is used for COPDPirenzipine and telenzipine are Ml specific and used for peptic ulcer diseaseHyoscine , dicyclomine , propantheline, oxyphenonium , clinidium are used as anti spasmodicDarifenacin and solefenacin are M3 specific and used for irritable bowel and over reactive bladderDicyclomine, flavoxate, oxybutynin are useful for treatment of urinary incontinenceTolterodine, festerodine, darifenacin, solefenacin are used for urinary incontinence