U01.05.021 Muscarinic antagonists

Muscarinic antagonists block the action of acetylcholine on muscarinic receptors, leading to a variety of therapeutic effects across different organ systems. These drugs are widely used in clinical practice for diverse applications ranging from ophthalmic procedures to managing motion sickness.

Overview of Muscarinic Antagonists

Drug	Organ System	Clinical Applications
Atropine, Homatropine, Tropicamide	Eye	Induces mydriasis (pupil dilation) and cycloplegia (paralysis of ciliary muscle).
Benztropine, Trihexyphenidyl	Central Nervous System (CNS)	Used in Parkinson disease (“Park my Benz”) and acute dystonia.
Glycopyrrolate	Gastrointestinal (GI), Respiratory	Parenteral: Preoperative reduction of airway secretions. Oral: Treats drooling and peptic ulcers.
Hyoscyamine, Dicyclomine	GI	Antispasmodics for irritable bowel syndrome (IBS).
Ipratropium, Tiotropium	Respiratory	Management of chronic obstructive pulmonary disease (COPD) and asthma (“I pray I can breathe soon!”).
Oxybutynin, Solifenacin, Tolterodine	Genitourinary	Reduces bladder spasms and urge urinary incontinence associated with an overactive bladder.
Scopolamine	CNS	Prevention and treatment of motion sickness.

Important Drugs and Applications by Organ System

1. Eye

Drugs: Atropine, Homatropine, Tropicamide
Applications:
- Mydriasis (for eye examinations).
- Cycloplegia (useful in refraction assessment).

2. Central Nervous System (CNS)

Drugs: Benztropine, Trihexyphenidyl
Applications:
- Parkinson’s disease symptom management (e.g., tremors, rigidity).
- Acute dystonia (as seen in extrapyramidal side effects of antipsychotics).

3. Gastrointestinal (GI) and Respiratory Systems

Drugs: Glycopyrrolate
Applications:
- Parenteral: Reduces airway secretions before surgery.
- Oral: Treats excessive drooling and peptic ulcers.

4. Gastrointestinal System

Drugs: Hyoscyamine, Dicyclomine
Applications:
- Reduces smooth muscle spasms in irritable bowel syndrome (IBS).

5. Respiratory System

Drugs: Ipratropium, Tiotropium
Applications:
- Improves airflow in patients with COPD or asthma.
- Provides long-lasting bronchodilation.

6. Genitourinary System

Drugs: Oxybutynin, Solifenacin, Tolterodine
Applications:
- Relieves symptoms of overactive bladder.
- Reduces urgency, frequency, and bladder spasms.

7. Motion Sickness

Drug: Scopolamine
Application:
- Prevents and treats motion sickness.

Points to Remember

Muscarinic antagonists block parasympathetic activity, leading to their diverse effects.
Mnemonics like “Park my Benz” (for Parkinson’s drugs) and “I pray I can breathe soon” (for respiratory drugs) help recall specific applications.
Side effects such as dry mouth, blurred vision, and urinary retention are common due to anticholinergic activity.
Use with caution in elderly patients to avoid exacerbating cognitive impairments.

Suggested Study Tips

Group drugs by their target organ systems to simplify memorization.
Practice clinical scenarios to understand their real-world applications.
Create flashcards with drug names, key actions, and uses.

Bibliography

Katzung, B. G., & Trevor, A. J. Basic and Clinical Pharmacology.
Goodman & Gilman’s The Pharmacological Basis of Therapeutics.

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