CHOLINERGIC vs. ANTICHOLINERGIC DRUGS — STUDY NOTES

CHOLINERGIC DRUG

Cholinergic drugs are medications that mimic or enhance the actions of acetylcholine (ACh) — the main neurotransmitter of the parasympathetic nervous system (“rest and digest”).

These drugs stimulate cholinergic receptors or increase ACh at the synapse.

Types of Cholinergic Drugs

1. Direct-acting agonists
   → Bind directly to muscarinic (M) or nicotinic (N) receptors to activate them.
   Examples: Acetylcholine, Bethanechol, Pilocarpine, Methacholine, Carbachol.

2. Indirect-acting agonists (AChE inhibitors)
   → Inhibit acetylcholinesterase, the enzyme that breaks down ACh.
   → This increases ACh levels at synapses.
   Examples: Neostigmine, Physostigmine, Pyridostigmine, Donepezil, Organophosphates.

Main Effects (Parasympathomimetic)

Think “Rest and Digest” — everything slows down except digestion and urination.

System	Effect
Heart	↓ Heart rate (bradycardia)
Lungs	Bronchoconstriction, ↑ secretions
Eyes	Miosis (pupil constriction), ↑ lacrimation
GI tract	↑ Motility, ↑ salivation
Bladder	↑ Urination (contracts detrusor muscle)
Glands	↑ Sweat, tears, saliva

Common Uses

• Glaucoma → Pilocarpine, Carbachol

• Urinary retention → Bethanechol

• Myasthenia gravis → Neostigmine, Pyridostigmine

• Alzheimer’s disease → Donepezil, Rivastigmine

• Anticholinergic toxicity → Physostigmine

Toxicity (Cholinergic Crisis)

Mnemonic: DUMBBELLS

| D | Diarrhea |
| U | Urination |
| M | Miosis |
| B | Bradycardia |
| B | Bronchorrhea/Bronchospasm |
| E | Emesis |
| L | Lacrimation |
| L | Lethargy |
| S | Salivation / Sweating |

ANTICHOLINERGIC DRUGS

Definition

Anticholinergic drugs (also called parasympatholytics) block acetylcholine from binding to muscarinic receptors.
→ This inhibits the parasympathetic nervous system, producing sympathetic-like (“fight or flight”) effects.

Mechanism of Action

• Competitive antagonists at muscarinic receptors (M1–M5)

• Block ACh effects in smooth muscle, glands, and CNS

Main Effects (Opposite of Cholinergic)

System	Effect
Heart	↑ HR (tachycardia)
Lungs	Bronchodilation, ↓ secretions
Eyes	Mydriasis (pupil dilation), ↓ accommodation (blurred vision)
GI tract	↓ Motility, ↓ salivation (constipation, dry mouth)
Bladder	Urinary retention
CNS	Sedation or confusion (especially elderly)
Glands	↓ Sweating → ↑ body temperature (“hot as a hare”)

Common Anticholinergic Drugs

Drug	Use
Atropine	Bradycardia, organophosphate poisoning, pre-op secretion reduction
Scopolamine	Motion sickness (transdermal patch)
Ipratropium, Tiotropium	COPD, asthma (bronchodilation)
Oxybutynin, Tolterodine, Solifenacin	Overactive bladder
Benztropine, Trihexyphenidyl	Parkinson’s disease
Glycopyrrolate	Pre-op secretion control, reduces drooling

Anticholinergic Toxicity

Mnemonic: 😈 “Hot as a hare, dry as a bone, blind as a bat, red as a beet, mad as a hatter.”

Phrase	Meaning
Hot as a hare	Fever, hyperthermia
Dry as a bone	Dry mouth, no sweating
Blind as a bat	Mydriasis, blurred vision
Red as a beet	Flushed skin
Mad as a hatter	Confusion, delirium
+	Tachycardia, urinary retention

Antidote: Physostigmine (AChE inhibitor that crosses BBB)

CHOLINERGIC vs. ANTICHOLINERGIC — QUICK COMPARISON

Feature	Cholinergic (Parasympathomimetic)	Anticholinergic (Parasympatholytic)
Neurotransmitter	Mimics or ↑ ACh	Blocks ACh
Heart	↓ HR	↑ HR
Lungs	Bronchoconstriction	Bronchodilation
Eyes	Miosis (pupil constrict)	Mydriasis (pupil dilate)
GI Tract	↑ Motility	↓ Motility
Bladder	↑ Urination	Urinary retention
Sweat/Skin	↑ Sweat	↓ Sweat, dry skin
CNS	Stimulation or sedation	Sedation, delirium (high dose)
Examples	Bethanechol, Pilocarpine, Neostigmine	Atropine, Scopolamine, Ipratropium