autonomics:antimuscarinics
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Antimuscarinics (Muscarinic Antagonists)
autonomics parasympathetic anticholinergic
Antimuscarinics block acetylcholine at muscarinic receptors and therefore inhibit parasympathetic activity.
They produce predictable organ effects — remembering the physiology is more important than memorizing drugs.
Antimuscarinics = “Turn OFF rest-and-digest” → Sympathetic-like effects
Muscarinic Receptors
| Receptor | Location | Normal Function |
|---|---|---|
| M1 | CNS, gastric parietal cells | Cognition, acid secretion |
| M2 | Heart | ↓ Heart rate |
| M3 | Smooth muscle & glands | Contraction & secretion |
Blocking these receptors produces opposite physiologic effects.
Core Physiologic Effects
- Dry as a bone → ↓ secretions
- Blind as a bat → mydriasis + cycloplegia
- Hot as a hare → ↓ sweating
- Red as a beet → vasodilation
- Mad as a hatter → delirium
Organ System Effects
| Organ | Parasympathetic Action | Antimuscarinic Effect |
|---|---|---|
| Eye | Constrict pupil | Mydriasis |
| Heart | Slow heart | Tachycardia |
| Lungs | Bronchoconstriction | Bronchodilation |
| GI | Motility & secretion | Constipation |
| Bladder | Detrusor contraction | Urinary retention |
| Glands | Salivation | Dry mouth |
Major Clinical Uses
Bronchodilation
Overactive Bladder
GI Antispasmodic
Motion Sickness / CNS
Ophthalmic Mydriasis
Adverse Effects
All antimuscarinics share predictable toxicity:
- Dry mouth
- Constipation
- Urinary retention
- Blurred vision
- Tachycardia
- Delirium (elderly)
Contraindications
- Narrow-angle glaucoma
- Urinary retention / BPH
- Elderly with cognitive impairment
Clinical Pearls
If a symptom involves excessive secretion or smooth muscle contraction → antimuscarinics treat it.
Common real-world uses:
- COPD bronchodilation
- Overactive bladder
- Motion sickness
- Organophosphate poisoning antidote (atropine)
Related Systems
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