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Cholinergics and Anti-cholinergics: Downloadable Resources (PDF & PPT)

Download comprehensive materials on cholinergics and anti-cholinergics in both PDF and PPT formats. These resources cover drugs that affect the cholinergic system, either by mimicking the action of acetylcholine (cholinergics) or by blocking its action (anti-cholinergics). Learn about their mechanisms of action, classifications, clinical uses, and potential side effects. Ideal for students, healthcare professionals, and anyone interested in pharmacology. Download now for convenient offline access.

Keywords: Cholinergics, Anti-cholinergics, PDF, PPT, Download, Acetylcholine, Muscarinic Receptors, Nicotinic Receptors, Parasympathetic, Pharmacology, Mechanism of Action, Side Effects, Cholinergic Agonists, Cholinergic Antagonists, Parasympathomimetics, Parasympatholytics, Muscarinic Agonists, Muscarinic Antagonists, Nicotinic Agonists, Nicotinic Antagonists.

Cholinergics and Anti-cholinergics: Mechanisms and Effects

Cholinergics and anti-cholinergics are two classes of drugs that interact with the cholinergic system, a part of the autonomic nervous system that uses acetylcholine (ACh) as its primary neurotransmitter. Cholinergics (also called parasympathomimetics) enhance cholinergic transmission, while anti-cholinergics (also called parasympatholytics) reduce it. This document provides a detailed overview of both drug classes.

The Cholinergic System

Acetylcholine (ACh) is synthesized from choline and acetyl-CoA by the enzyme choline acetyltransferase. After release from the presynaptic neuron, ACh binds to cholinergic receptors on the postsynaptic neuron or target tissue. ACh is rapidly broken down by the enzyme acetylcholinesterase (AChE), terminating its action.

There are two main types of cholinergic receptors:

• Muscarinic Receptors: G protein-coupled receptors. There are five subtypes (M1-M5), found in various locations:
  • M1: Nerves
  • M2: Heart, nerves, smooth muscle
  • M3: Glands, smooth muscle, endothelium
  • M4: CNS
  • M5: CNS

  Activation of muscarinic receptors produces a variety of effects, including:

  • Decreased heart rate (M2)
  • Increased smooth muscle contraction (e.g., in the GI tract, bladder, bronchi) (M3)
  • Increased glandular secretions (e.g., saliva, sweat, tears, gastric acid) (M3)
  • Vasodilation (M3, via release of nitric oxide from endothelium)
  • Miosis (constriction of the pupil) (M3)
• Nicotinic Receptors: Ligand-gated ion channels. Found at:
  • Neuromuscular junction (skeletal muscle)
  • Autonomic ganglia (both sympathetic and parasympathetic)
  • Adrenal medulla
  • Central nervous system (CNS)

  Activation of nicotinic receptors causes:

  • Skeletal muscle contraction
  • Stimulation of autonomic ganglia
  • Release of epinephrine from the adrenal medulla
  • Various CNS effects

Cholinergics (Parasympathomimetics)

Cholinergic drugs enhance cholinergic transmission. They can be classified based on their mechanism of action:

• Direct-Acting Cholinergic Agonists: Bind directly to and activate cholinergic receptors (muscarinic or nicotinic).
  • Muscarinic Agonists:
    • Acetylcholine (limited clinical use due to rapid breakdown)
    • Bethanechol (used to treat urinary retention and gastrointestinal atony)
    • Pilocarpine (used to treat glaucoma and dry mouth)
    • Cevimeline (used to treat dry mouth in Sjögren's syndrome)
  • Nicotinic Agonists:
    • Nicotine (found in tobacco; limited therapeutic use)
    • Varenicline (used for smoking cessation)
• Indirect-Acting Cholinergic Agonists (Cholinesterase Inhibitors): Inhibit the enzyme acetylcholinesterase (AChE), which breaks down ACh. This increases the concentration of ACh at cholinergic synapses, prolonging its action.
  • Reversible Cholinesterase Inhibitors:
    • Physostigmine (can cross the blood-brain barrier)
    • Neostigmine (does not cross the blood-brain barrier well)
    • Pyridostigmine (used to treat myasthenia gravis)
    • Edrophonium (short-acting; used to diagnose myasthenia gravis)
    • Donepezil, Rivastigmine, Galantamine (used to treat Alzheimer's disease)
  • Irreversible Cholinesterase Inhibitors: Form a very stable bond with AChE, leading to long-lasting inhibition. Many are highly toxic organophosphates (nerve gases, insecticides).
    • Echothiophate (used to treat glaucoma)
    • Malathion (insecticide)
    • Sarin, Soman, Tabun (nerve gases)

Clinical Uses of Cholinergics:

• Glaucoma
• Myasthenia gravis
• Alzheimer's disease
• Urinary retention
• Postoperative ileus (intestinal paralysis)
• Reversal of neuromuscular blockade
• Antidote for anticholinergic poisoning
• Smoking cessation.

Side Effects of Cholinergics (Muscarinic Excess): "SLUDGE" (Salivation, Lacrimation, Urination, Defecation, Gastrointestinal distress, Emesis) and also bradycardia, bronchoconstriction, miosis, and sweating.

Anti-cholinergics (Parasympatholytics)

Anti-cholinergic drugs block the action of acetylcholine at cholinergic receptors. They are primarily classified based on their receptor selectivity:

• Muscarinic Antagonists (Antimuscarinics): Block muscarinic receptors. Examples include:
  • Atropine (non-selective; can cross the blood-brain barrier)
  • Scopolamine (used to treat motion sickness; can cross the blood-brain barrier)
  • Ipratropium, Tiotropium (used as bronchodilators in asthma and COPD)
  • Oxybutynin, Tolterodine, Solifenacin, Darifenacin (used to treat overactive bladder)
  • Benztropine, Trihexyphenidyl (used to treat Parkinson's disease and drug-induced extrapyramidal symptoms)
  • Homatropine, Cyclopentolate, Tropicamide: Induce mydriasis and cycloplegia for opthalmic examination.
• Nicotinic Antagonists: Block nicotinic receptors.
  • Ganglionic Blockers: Block nicotinic receptors at autonomic ganglia. Have many side effects due to blockade of both sympathetic and parasympathetic ganglia. Rarely used clinically. Example: Mecamylamine, Hexamethonium, Trimethaphan.
  • Neuromuscular Blockers: Block nicotinic receptors at the neuromuscular junction, causing muscle paralysis. Used during surgery to relax muscles.
    • Non-depolarizing Neuromuscular Blockers: (e.g., Tubocurarine, Atracurium, Cisatracurium, Vecuronium, Rocuronium). Competitive antagonists of ACh at the neuromuscular junction.
    • Depolarizing Neuromuscular Blockers: (e.g., Succinylcholine). Initially activate the nicotinic receptor, causing muscle fasciculations (twitching), followed by persistent depolarization and paralysis.

Clinical Uses of Anti-cholinergics:

• Asthma and COPD (ipratropium, tiotropium)
• Overactive bladder (oxybutynin, tolterodine)
• Motion sickness (scopolamine)
• Parkinson's disease (benztropine, trihexyphenidyl)
• Antidote for cholinergic poisoning (atropine)
• Bradycardia (atropine)
• Mydriasis and cycloplegia for eye exams (tropicamide, cyclopentolate)
• Preoperative medication to reduce secretions and prevent bradycardia (atropine, glycopyrrolate)
• Irritable bowel syndrome (dicyclomine, hyoscyamine)
• Neuromuscular blockade during surgery (neuromuscular blockers)

Side Effects of Anti-cholinergics (Antimuscarinic Effects): Dry mouth, blurred vision, constipation, urinary retention, tachycardia, confusion, drowsiness, and anhidrosis (decreased sweating). "Dry as a bone, red as a beet, blind as a bat, mad as a hatter, hot as a hare."

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