Learning Objective
Recall the major direct-acting muscarinic agonists, their receptor selectivity, AChE sensitivity, and clinical uses.
Key Drugs and Properties
| Drug | Receptor Activity | AChE Hydrolysis | Clinical Use |
|---|---|---|---|
| ACh | M & N | +++ | Short half-life → no clinical use |
| Bethanechol | M | − | Postoperative/neurogenic ileus, urinary retention |
| Methacholine | M > N | + | Diagnosis of bronchial hyperreactivity |
| Pilocarpine, Cevimeline | M | − | Pilocarpine → glaucoma; Pilocarpine/Cevimeline → xerostomia |
Activity
Clinical Correlation
High-Yield Notes
- ACh: Rapidly hydrolyzed → impractical for therapy.
- Bethanechol: Resistant to AChE → useful for bladder and bowel atony.
- Methacholine: Slightly resistant → diagnostic only.
- Pilocarpine/Cevimeline: Resistant → used for secretory disorders and glaucoma.
- Alzheimer therapy: Focuses on AChE inhibition, not direct agonists.
