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Pharma-Cholinoceptor-blocking drugs.pptx
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- 2. Overview • The cholinergicantagonists bind to cholinoceptors, but they do not trigger the usual receptor-mediated intracellular effects • Also called cholinergic blockers, parasympatholytics or anticholinergic drugs • Cholinoceptor antagonists are divided into muscarinic and nicotinic subgroups on the basis of their receptor affinities
- 3. Overview • Cholinergic antagonistsare subdivided according to their physiological site of action: • Muscarin antagonists (antamuscarinics, parasympatholytic drugs) • Ganglionic blockers • Neuromuscular-blocking drugs
- 4. Neuromuscular junction Effector organ Sympathatic Neuromuscular junction Adre nal medu lla Ganglionic transmittio n Neuroeffect or transmittio n Parasympathatic Sympathatic innervation of adrenal medulla Somatic Effectororgan α or β Adrenergic receptor Ganglion ic blockers antimuscarin ics Neuromuscular blockers NN receptor NN receptor NN receptor Acetylcholine Norepinephri ne
- 5. Muscarinic antagonists (antimuscarinics) •These are reversible (surmountable) competitive antagonists that compete with ACh and other muscarinic agonists for a common binding site on the muscarinic receptor • These drugs block sympathetic neurons that are cholinergic innervating salivary and sweat glands • The antimuscarinics are beneficial in a variety of clinical situations, because they do not block nicotinic receptors
- 6. Muscarinic antagonists (antimuscarinics) •The class of drugs includes: • Naturally occurring alkaloids (atropine & scopolamine) • Semisynthetic derivatives of the naturally occurring alkaloids, which primarily differ from the parent compounds in their disposition in the body or their duration of action • Synthetic muscarinic antagonists (homatropine & tropicamide) , some of which show selectivity for particular subtypes of muscarinic receptors
- 7. Muscarinic antagonists • Atropine(prototype) does not distinguish among the M1, M2, and M3 subgroups of muscarinic receptors • Few synthetic antimuscarinic drugs demonstrate selectivity for one or another of these subgroups: • M1 selective agents: pirenzepine, telenzepine • M3 selective agents: darifenacin, solifenacin
- 8. Organ Effect Mechanism CNSSedation, anti-motion sickness action, antiparkinson action, amnesia, delirium Block of muscarinic receptors, several subtypes Eye Cycloplegia (paralysis of the ciliary muscle of the eye), mydriasis Block of M3 receptors Bronchi Bronchodilation, especially if constricted Block of M3 receptors GIT Relaxation, slowed peristalsis, reduced salivation Block of M1, M3 receptors Genitourinary tract Relaxation of bladder wall, urinary retention Block of M3 and possibly M1 receptors Heart Bradycardia (at low doses) Tachycardia (at high doses) Block of presynaptic M1 receptors Block of M2 receptors in the sinoatrial node Blood vessels Block of muscarinic vasodilation; not manifest unless a muscarinic agonist is present Block of M3 receptors on endothelium of vessels Glands Marked reduction of salivation; moderate reduction of lacrimation, sweating; less reduction of gastric secretion Block of M1, M3 receptors Effects of muscarinic blocking drugs
- 9. Muscarinic antagonists Clinical uses CentralNervous System Disorders 1. Parkinson's Disease: Benzotropine, biperiden, and trihexylphenidyl 2. Motion Sickness: Scopolamine (injection or by mouth or as a transdermal patch)
- 10. Muscarinic antagonists Clinical uses •Ophthalmologic Disorders • Examination of the retina and optic disc and for the accurate measurement of refractive error administered topically as eye drops or ointment • Agents used: Atropine, scopolamine, cyclopentolate and tropicamide, homatropin • Short-acting drugs (e.g cyclopentolate and tropicamide) are favoured for ophthalmic application b/c complete recovery of accommodation occurs within 6 to 24 hours and 2 to 6 hours, respectively
- 11. Muscarinic antagonists Clinical uses •Respiratory disorders: Ipratropium, tiotropium are used as an inhalational drug in asthma & chronic obstruction pulmonary disease (COPD) • Gastrointestinal disorders Treatment of traveler's diarrhea: in combination with an opioid antidiarrheal drug (e.g. atropine & diphenoxylate combination • Urinary Disorders Symptomatic relief in the treatment of urinary urgency caused by minor inflammatory bladder disorders Relief bladder spasm after urologic surgery eg. prostatectomy: Oxybutynin , darifenacin, solifenacin , tolterodine, fesoterodine (all are selective M3 antagonists), trospium (a nonselective antagonist)
- 12. Muscarinic antagonists Clinical uses •Cholinergic poisoning • Used for the treatment of poisoning caused by anticholinesterase organophosphorus insecticides or by the ingestion of mushrooms of Inocybe genus • Atropine is used to antagonize/reverse the central and parasympathomimetic effects of the organophosphate anticholinesterase inhibitors
- 13. Toxicity (Adverse effect)of antimuscarinic agents • Depend on the dose • Includes: dry mouth, blurred vision ‘sandy eyes’, tachycardia, and constipation • In children-Atropine fever (hyperthermic effects of atropine) • In elderly are susceptible to antimuscarinic toxicities including the eye and the bladder especially those with a history of prostatic hyperplasia
- 14. Contraindications • Contraindications tothe use of antimuscarinic drugs are relative, not absolute • Antimuscarinic drugs are contraindicated in patients with glaucoma and elderly patients with a history of prostatic hyperplasia • Because the antimuscarinic drugs slow gastric emptying, they may increase symptoms in patients with gastric ulcer • (nonselective antimuscarinic agents should never be used to treat acid-peptic disease)