cholinergic vs anticholinergic - brief explanation
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I have enough from the textbooks to give a clear, concise answer. Here's the breakdown:
Cholinergic vs Anticholinergic
The Core Concept
Both act on receptors activated by acetylcholine (ACh) — the neurotransmitter of the parasympathetic nervous system (and somatic motor neurons, autonomic ganglia, and some sympathetic fibers like sweat glands).
- Cholinergic = mimics or enhances ACh activity
- Anticholinergic = blocks ACh activity (specifically muscarinic receptors, so often called "antimuscarinic")
Receptors Involved
| Receptor | Location | Notes |
|---|---|---|
| Muscarinic (M1–M5) | Heart, smooth muscle, glands, CNS | Main target of anticholinergics |
| Nicotinic (NM, NN) | Skeletal muscle, autonomic ganglia | Less targeted by classic anticholinergics |
Cholinergic Effects (SLUDGE / DUMBELS mnemonic)
Activation of muscarinic + nicotinic receptors produces:
| System | Effect |
|---|---|
| Salivary/lacrimal/sweat glands | Increased secretions |
| GI | ↑ motility, nausea, vomiting, diarrhea, cramps |
| Urinary | Increased urination (detrusor contraction) |
| Eyes | Miosis (pupil constriction), ↑ lacrimation |
| Heart | Bradycardia, ↓ BP |
| Lungs | Bronchoconstriction, ↑ secretions |
| Skeletal muscle (nicotinic) | Fasciculations → paralysis (in excess) |
| CNS | Seizures (in toxicity) |
Classic causes: Organophosphate poisoning, nerve agents, cholinesterase inhibitor overdose (e.g. neostigmine, physostigmine)
Anticholinergic Effects ("Hot as a hare, dry as a bone, red as a beet, mad as a hatter, blind as a bat")
Blockade of muscarinic receptors produces the opposite:
| System | Effect |
|---|---|
| Glands | Dry mouth, dry skin, ↓ sweating |
| GI | ↓ motility, constipation |
| Urinary | Urinary retention |
| Eyes | Mydriasis (pupil dilation), blurred vision |
| Heart | Tachycardia |
| Lungs | Bronchodilation, ↓ secretions |
| Skin | Flushed, hot |
| CNS | Confusion, delirium, agitation, hallucinations |
Classic causes: Atropine, scopolamine, antihistamines (diphenhydramine), TCAs, antipsychotics, plants (belladonna, jimsonweed)
Drug Classes
| Category | Mechanism | Examples |
|---|---|---|
| Direct cholinergic agonists | Bind ACh receptors directly | Bethanechol, pilocarpine, carbachol |
| Indirect cholinergic agonists (AChE inhibitors) | Block acetylcholinesterase → ↑ ACh | Neostigmine, donepezil, pyridostigmine |
| Irreversible AChE inhibitors | Organophosphates | Echothiophate, nerve agents |
| Anticholinergics | Block muscarinic receptors | Atropine, ipratropium, oxybutynin, benztropine |
Clinical Pearl: Toxidromes
In emergency medicine, these two toxidromes are classically opposed:
- Cholinergic toxidrome: wet, bradycardic, miotic — treat with atropine (+ pralidoxime for organophosphates)
- Anticholinergic toxidrome: dry, tachycardic, mydriatic, flushed, delirious — treat with physostigmine (a cholinesterase inhibitor)
— Rosen's Emergency Medicine; Lippincott Illustrated Reviews: Pharmacology
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