Muscarinic Antagonists (Anti-Muscarinic Medications)

Overview

Muscarinic Antagonists prevent muscarinic receptors in the parasympathetic nervous system from being stimulated by acetylcholine (ACh).

Central Nervous System (CNS): Brain and Spinal Cord.
Peripheral Nervous System (PNS):
- Somatic Nervous System: Controls voluntary movement of skeletal muscles.
- Autonomic Nervous System: Divided into sympathetic and parasympathetic nervous systems.

Function: Controls involuntary actions like digestion, urination, etc.
Pathway:
- Signals originate in hypothalamus and synapse in brain stem or spinal cord.
- Preganglionic neurons target parasympathetic ganglions near target organs.
- Postganglionic neurons release acetylcholine (ACh), stimulating muscarinic receptors for 'rest and digest' effects.

Heart: Slows heart rate.
Gastrointestinal: Increases motility for digestion.
Bladder: Causes detrusor muscle contraction (urination).
Glands: Increases salivary/sweat/lacrimal secretions.
Liver: Triggers glucose storage.
Lungs: Causes bronchoconstriction.
Eyes: Causes pupil constriction (miosis) and reduces intraocular pressure.
Brain: Generally stimulant effects, controlling movement and preventing vomiting.

Mechanism: Block ACh on muscarinic receptors.
Atropine:
- Uses: Treat bradycardia, nocturnal enuresis, pupil dilation, antidote for organophosphate poisoning.
- Side Effects: Tachycardia, constipation, urinary retention, dry mouth/skin/eyes, blurry vision, hypothermia, dizziness, confusion.
- Contraindications: Narrow-angle glaucoma.

Oxybutynin: Targets bladder, reduces detrusor muscle spasms, treats urge incontinence.
Ipratropium & Tiotropium:
- Use: Bronchodilators for COPD and asthma.
- Characteristics: Ipratropium is short-acting; Tiotropium is long-acting.

Scopolamine: Prevents motion sickness by acting on the brain's vomiting center.
Benztropine & Trihexyphenidyl: Used in Parkinson’s disease to restore cholinergic-dopaminergic balance, reducing tremors.
- CNS Side Effects: Sedation, mental confusion.

Atropine Mnemonic: Tropical island setting with a boy covering enuresis with a heart (bradycardia), empty water bottle (dryness), and a closed porta-potty (urinary retention).
Organ-Specific Mnemonics:
- Oxybutynin: Oxygen tank inflating a bladder.
- Ipratropium: Short palm tree with a rat (short-acting).
- Tiotropium: Tall palm tree with ties (long-acting).
- Parkinson’s: Parking spot with a Mercedes-Benz.
- Scopolamine: Scallop vomiting from motion sickness.

Inhibition: Muscarinic antagonists inhibit ACh effects.
Main Drugs: Atropine, Oxybutynin, Ipratropium, Tiotropium, Scopolamine, Benztropine, Trihexyphenidyl.
Side Effects: Tachycardia, constipation, dry mouth/skin/eyes, blurry vision, hypothermia, confusion.
Contraindication: Narrow-angle glaucoma.

Stay tuned for a mind map and more mnemonics to help remember pharmacological details.