Lecture on Anti-Muscarinic Agents

Introduction

• Topic: Anti-muscarinic agents
• Purpose: Discuss physiology and pharmacology of anti-muscarinic agents
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Overview of Parasympathetic Nervous System

• Acetylcholine: Main neurotransmitter
• Receptors:
  • Muscarinic Receptors
  • Nicotinic Receptors
• Function:
  • Modulate movement (Basal Ganglia)
  • Control vomiting (Emetic Center)
  • Pupil constriction & accommodation (Eye)
  • Secretion (Lacrimal & Salivary Glands)
  • Heart rate control
  • Bronchoconstriction
  • GI motility and secretion
  • Sweat production
  • Bladder contraction

Physiological Mechanism

• Balance of movement: Dopamine vs. Acetylcholine
• Muscarinic Receptors:
  • M2 & M4 (Inhibitory): Primarily in the heart
  • M1, M3, M5 (Stimulatory): Other organs

Anti-Muscarinic Agents

• Mechanism: Block acetylcholine at muscarinic receptors, opposing parasympathetic actions.

Drug Examples

1. Atropine

   • Induces pupil dilation (used in ‘lazy eye’ aka amblyopia)
   • Increases heart rate (used in bradycardia)
   • Reduces secretions (pre-intubation)
   • Antidote for cholinergic crisis

2. Scopolamine

   • Prevents motion sickness
   • Reduces post-operative nausea and vomiting

3. Benztropine & Trihexyphenidyl

   • Used in Parkinson's disease to manage tremors
   • Address extrapyramidal symptoms from antipsychotics

4. Oxybutynin, Tolterodine, Solifenacin

   • Treat urinary incontinence
   • Manage overactive bladder

5. Dicyclomine (Bentyl) & Hyoscyamine

   • Used in IBS-D to reduce GI spasms

6. Glycopyrrolate

   • Reduces drooling and respiratory secretions

7. Ipratropium (Atrovent) & Tiotropium (Spiriva)

   • Bronchodilators for COPD and asthma
   • Ipratropium (short-acting), Tiotropium (long-acting)

Toxicity and Contraindications

• Anti-cholinergic Toxicity:
  • Causes: Overdose of anti-muscarinic agents, antipsychotics
  • Symptoms: Delirium, pupil dilation (mydriasis), tachycardia, fever
  • Treatment: Physostigmine (acetylcholinesterase inhibitor)
• Contraindications: Glaucoma, GI obstructions, urinary retention.