Action of physiostigmine and neostigmine
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Finding Sources
Reading File
Reading File
Reading File
Loading Image
I now have comprehensive information. Let me compile the full answer.
Physostigmine vs. Neostigmine: Mechanism and Actions
Both are reversible anticholinesterase (AChE inhibitor) agents - they inhibit the enzyme acetylcholinesterase, preventing the breakdown of acetylcholine (ACh). This leads to accumulation of ACh at all cholinergic synapses.
Physostigmine
Chemical Nature
- A naturally occurring nitrogenous carbamic acid ester found in the Calabar bean (Physostigma venenosum)
- Tertiary amine - lipid soluble
Mechanism
- Acts as a substrate for AChE, forming a relatively stable carbamoylated intermediate that reversibly inactivates the enzyme
- This potentiates cholinergic activity throughout the body
Actions
| System | Effect |
|---|---|
| GI tract | Increased smooth muscle contraction, increased motility, increased salivary/gastric secretions |
| Eye | Miosis (constriction of pupil), ciliary muscle contraction (spasm of accommodation) |
| Cardiovascular | Bradycardia, hypotension |
| Skeletal muscle | Fasciculations and twitches (nicotinic NMJ stimulation); paralysis at high doses |
| CNS | Stimulates CNS cholinergic sites - can reverse anticholinergic CNS toxicity |
Because of its tertiary amine structure, physostigmine crosses the blood-brain barrier and acts centrally.
Therapeutic Uses
- Treatment of anticholinergic drug overdose (e.g., atropine toxicity) - especially where CNS effects need reversal
- Open-angle glaucoma (historically, as eye drops)
Duration of Action
- 30 minutes to 2 hours (intermediate-acting)
Adverse Effects
- Bradycardia, decreased cardiac output
- Convulsions at high doses
- Skeletal muscle paralysis (theoretical at therapeutic doses, rarely seen)
Neostigmine
Chemical Nature
- A synthetic carbamic acid ester
- Quaternary amine - polar and water soluble
Mechanism
- Reversibly inhibits AChE in a manner similar to physostigmine (carbamoylation of AChE)
Actions
| System | Effect |
|---|---|
| GI/Bladder | Stimulates smooth muscle, increases motility, promotes urination |
| Skeletal muscle | More pronounced effect than physostigmine - stimulates contractility before paralysis |
| CNS | No CNS effects - cannot cross the blood-brain barrier (quaternary amine) |
| Cardiovascular | Bradycardia, hypotension (peripheral muscarinic) |
Therapeutic Uses
- Reversal of non-depolarizing (competitive) neuromuscular blockade (e.g., reversal of vecuronium, pancuronium)
- Myasthenia gravis - symptomatic management
- Bladder atony and GI atony (post-operative ileus, urinary retention)
Duration of Action
- 30 minutes to 2 hours (intermediate-acting)
Adverse Effects
- Generalized cholinergic stimulation: salivation, flushing, hypotension, nausea, diarrhea, bronchospasm
- No CNS side effects
- Contraindicated in intestinal or urinary bladder obstruction
Key Differences at a Glance
| Feature | Physostigmine | Neostigmine |
|---|---|---|
| Source | Natural (Calabar bean) | Synthetic |
| Amine type | Tertiary amine | Quaternary amine |
| BBB penetration | Yes (CNS active) | No (peripherally restricted) |
| Skeletal muscle effect | Moderate | Greater (stimulates before paralysis) |
| Main clinical use | Anticholinergic overdose (CNS reversal) | NMJ block reversal; myasthenia gravis |
| GI absorption | Good | Poor |
| CNS toxicity reversal | Yes | No |
| Duration | 30 min - 2 hr | 30 min - 2 hr |
Key exam point: Physostigmine = tertiary amine = crosses BBB = used for central anticholinergic toxicity. Neostigmine = quaternary amine = does NOT cross BBB = used for peripheral NMJ reversal and myasthenia gravis.
Sources: Lippincott Illustrated Reviews: Pharmacology, pp. 161-163; Katzung's Basic and Clinical Pharmacology, 16e; Goodman & Gilman's Pharmacological Basis of Therapeutics
6880f82f-2324-4411-95ae-b2c00e82d39f.jpeg
Give answer with explanation
analyse_media
Reading File
Here is a clean summary of all answers:
Surgery MCQ - Answer Sheet
| Q | Answer | Key Point |
|---|---|---|
| 1 | (b) Sacrum | Most common site of pressure sore in supine patients |
| 2 | (b) Proximal jejunum | Ileum/colon critical for fluid-electrolyte; proximal jejunum resection best tolerated |
| 3 | (c) Bicarbonate / Base deficit | Best ABG marker of systemic perfusion - reflects anaerobic metabolism |
| 4 | (c) I, II and III | Phrygian cap, floating GB, absent GB are congenital; Sngalian is not standard |
| 5 | (d) I, III and IV | GB = reservoir, mucus secretion, bile concentration; bile PRODUCTION is by liver |
| 6 | (d) Abdominal discomfort and ascites | BCS presents with abdominal pain, ascites, hepatomegaly; caudate lobe hypertrophies |
| 7 | (b) Usually in main arterial trunk | Splenic artery aneurysm - distal/mid artery; more common in women |
| 8 | (b) I, II and IV | Head injury primary survey: oxygenation + circulation, exclude hypoglycemia, pupils |
| 9 | (d) I, II, III and IV | All ABCDE components correct: Airway, Breathing, Circulation, Disability |
| 10 | (c) II, III and IV | Inguinal hernia in children: more in premature boys, repair promptly, may transilluminate |
| 11 | (a) I, II and III | Late dumping: 1-3 hrs post meal, tremor/faintness (hypoglycemia), lasts ~30 min |
| 12 | (c) Medical therapy has no role | This is FALSE - fluids, NGT, PPIs, H. pylori eradication all have a role |
Note: The image resolution made a few options slightly difficult to read precisely. If any answer doesn't match your answer key, let me know the specific question and I'll re-examine it.
This is a shared conversation. Sign in to Orris to start your own chat.