๐ง Acetylcholine and Cholinergic Drugs for USMLE Step 1: Direct & Indirect Agonists, Receptor Actions, and Toxicities
Acetylcholine (ACh) is a cornerstone neurotransmitter in both the central and peripheral nervous system, and the target of numerous drugs and toxins.
On Step 1, youโll encounter it in:
Pharmacology
Toxicology
Neuro and GI systems
Understanding the types of receptors, drug classes, and clinical applications will help you reason through complex vignettes.
๐ฌ ACh Receptors: Muscarinic vs Nicotinic
Receptor Type | Location | Mechanism | Effects |
---|---|---|---|
Muscarinic (M1โM5) | Parasympathetic target organs | G-protein coupled | SLUDGE effects |
Nicotinic (Nn, Nm) | Ganglia, NMJ, adrenal medulla | Ligand-gated ion channel | Sympathetic activation, muscle contraction |
๐ง Step 1 loves receptor type-to-organ and drug matchups
๐ Cholinergic Agonists
Drug | Type | Use |
---|---|---|
Bethanechol | Direct | Urinary retention |
Pilocarpine | Direct | Glaucoma, dry mouth |
Neostigmine | Indirect | Myasthenia, ileus |
Physostigmine | Indirect | Anticholinergic toxicity |
โ ๏ธ Cholinergic Toxicity
SLUDGE-M Mnemonic
Salivation
Lacrimation
Urination
Diarrhea
GI cramps
Emesis
Miosis, Muscle fasciculations
Organophosphates (e.g., parathion, sarin gas)
Irreversibly inhibit AChE โ toxic ACh buildup
๐งช Step 1 Case Clue: Farmer exposed to pesticide with pinpoint pupils, wheezing, bradycardia
๐ Antidote: Atropine + Pralidoxime
Drug | Mechanism | Notes |
---|---|---|
Atropine | Muscarinic antagonist | Treats SLUDGE; no effect on nicotinic symptoms |
Pralidoxime | Regenerates AChE | Effective before enzyme aging in organophosphate poisoning |
๐ง Step 1 Clinical Clue
A patient treated for myasthenia with neostigmine presents with diarrhea, salivation, and miosis. How do you distinguish cholinergic crisis from MG worsening?
โ Give edrophonium
If improves: MG exacerbation
If worsens/no change: Cholinergic crisis
๐ง Mnemonics
โHot as a hare, dry as a bone, blind as a batโฆโ โ Atropine toxicity
โDUMBELSโ for organophosphate symptoms
Diarrhea, Urination, Miosis, Bradycardia, Emesis, Lacrimation, Salivation
๐ฏ Final Review Table
Drug Class | Examples | Main Uses |
---|---|---|
Direct agonists | Bethanechol, Pilocarpine | Stimulate bladder, saliva, and eye drainage |
AChE inhibitors | Neostigmine, Donepezil | Myasthenia gravis, Alzheimerโs |
Anticholinergics | Atropine, Scopolamine | Bradycardia, motion sickness, GI cramping |
๐ Call-to-Action
Want to master neuropharm with visual-first learning?
๐ฏ Try the KOTC Visual QBank and Game-Based Learning Platform now:
๐ https://kingofthecurve.org/trial-sessions
๐ Or unlock all pharmacology illustrations with lifetime access:
๐ https://kingofthecurve.org/free-lifetime
Frequently Asked Questions (FAQs)
-
Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.
-
Practice mindfulness techniques, take practice exams under realistic conditions, and maintain a balanced lifestyle.
-
Set short-term goals, seek support from mentors, and reward yourself for small achievements.
-
Regular exercise improves focus, reduces stress, and enhances overall mental clarity.
-
KOTC offers personalized learning tools, gamification features, and adaptive question banks to help students stay on track without burnout.