Parasympathomimetic Drugs Cholinomimetics
parasympathomimetic drugscholinomimetic drugsmuscarinic agonistsnicotinic agonistsbethanechol side effectspilocarpine adverse effectsneostigmine toxicitypyridostigmine overdoserivastigmine side effectsdonepezil bradycardiacholinergic crisisedrophonium testphysostigmine seizuresorganophosphate poisoningcholinergic toxicitymuscarinic effectsnicotinic effectsM3 receptor stimulationcholinesterase inhibitorsautonomic pharmacologyglaucoma drugs adverse effectsMG treatment complicationsparasympathetic overstimulationbronchospasm side effectmiosis side effectsGI hypermotility effectsmuscarinic receptor adverse reactionspharmacology MCQsNEET PG pharmacologymedical case scenariosdrug-induced side effectshigh-yield pharmacology
Below is a **complete, concise-but-exhaustive medical note on *Parasympathomimetic Drugs*** following your preferred NEET-PG/MBBS/MD style.
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# **Parasympathomimetic Drugs (Cholinomimetics) – Complete Detailed Note**
Parasympathomimetic drugs **mimic the actions of the parasympathetic nervous system**, primarily by **stimulating muscarinic and/or nicotinic acetylcholine receptors** or by **inhibiting acetylcholinesterase** → ↑ ACh at synapse.
They are classified into **direct-acting** (act on receptors) and **indirect-acting** (AChE inhibitors).
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# **1. PHYSIOLOGY & MECHANISM**
Parasympathetic activation =
* **M1**: CNS, gastric glands → cognitive effects, secretion.
* **M2**: Heart → ↓ HR, ↓ AV conduction.
* **M3**: Smooth muscle & glands → miosis, bronchoconstriction, ↑ secretions, ↑ urination, ↑ GI motility.
* **Nn**: Ganglia.
* **Nm**: Neuromuscular junction.
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# **2. CLASSIFICATION**
## **A. Direct-Acting Parasympathomimetics (Muscarinic agonists)**
1. **Choline esters**
* Acetylcholine
* **Bethanechol**
* Carbachol
* Methacholine
2. **Alkaloids**
* **Pilocarpine**
* Muscarine
* Arecoline
3. **Synthetic agonists**
* Cevimeline (for Sjögren)
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## **B. Indirect-Acting Parasympathomimetics (AChE Inhibitors)**
### **Reversible**
* **Edrophonium**
* **Neostigmine**
* **Pyridostigmine**
* **Physostigmine**
* **Rivastigmine**, Donepezil, Galantamine (Alzheimer’s)
### **Irreversible (Organophosphates)**
* **Echothiophate** (clinical)
* **Parathion, malathion**
* Novichok, VX, Sarin (toxins)
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# **3. DRUG DETAILS (MECHANISM, USES, DOSE, EFFECTS, CONTRAINDICATIONS)**
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## **A. DIRECT ACTING**
### **1. Bethanechol**
**MOA:** M3 agonist → ↑ detrusor tone, ↑ GI motility.
**Uses:**
* **Urinary retention** (postpartum, post-op)
* **Neurogenic bladder**
**Dose:** 10–50 mg PO 3–4×/day
**SE:** sweating, salivation, bronchospasm, hypotension, diarrhea
**Contra:** Asthma, peptic ulcer, CAD, obstruction
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### **2. Carbachol**
**MOA:** Nicotinic + muscarinic agonist
**Uses:**
* Glaucoma (rare now)
**SE:** Severe miosis, bronchospasm
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### **3. Pilocarpine**
**MOA:** M3 agonist, ↑ secretion, miosis
**Uses:**
* **Acute angle-closure glaucoma**
* **Chronic glaucoma**
* **Sjögren syndrome** (dry mouth)
**Dose:**
* Ophthalmic drops: 1–4%
* Oral: 5–10 mg TID
**SE:** headache, brow ache, sweating
**Contra:** uncontrolled asthma
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### **4. Cevimeline**
**MOA:** M3 selective agonist
**Uses:** Sjögren syndrome
**SE:** sweating, visual disturbance
---
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## **B. INDIRECT ACTING – REVERSIBLE**
### **1. Edrophonium (Very short acting)**
**MOA:** AChE inhibition
**Uses:**
* Tensilon test for MG
* Differentiate MG crisis vs cholinergic crisis
**SE:** bradycardia, diarrhea
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### **2. Neostigmine**
**MOA:** AChE inhibitor + some direct Nm action
**Uses:**
* **Myasthenia gravis**
* Post-operative **ileus**
* **Urinary retention**
* Reversal of **non-depolarizing muscle relaxants**
**Dose:** 15 mg PO every 6 hours; IV 0.04–0.07 mg/kg
**SE:** salivation, diarrhea, bronchospasm
**Contra:** asthma, obstruction
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### **3. Pyridostigmine**
**MOA:** AChE inhibitor
**Uses:**
* **Chronic MG treatment (first line)**
**Dose:** 30–60 mg PO 3–6×/day
**SE:** same as neostigmine
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### **4. Physostigmine**
**MOA:** Lipid soluble, crosses BBB
**Uses:**
* **Anticholinergic toxicity antidote** (atropine, antihistamines, TCA)
**SE:** seizures (important)
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### **5. Rivastigmine / Donepezil / Galantamine**
**Uses:**
* **Alzheimer’s disease**
**SE:** nausea, bradycardia, syncope
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---
## **C. INDIRECT ACTING – IRREVERSIBLE**
### **Organophosphates**
**MOA:** Permanently inhibit AChE → cholinergic crisis
**Effects:** DUMBBELSS
* Diarrhea
* Urination
* Miosis
* Bronchospasm
* Bradycardia
* Emesis
* Lacrimation
* Salivation
* Sweating
**Management:**
* **Atropine** (blocks muscarinic)
* **Pralidoxime (2-PAM)** before aging
* Benzodiazepines for seizures
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# **4. CLINICAL EFFECTS OF PARASYMPATHOMIMETICS**
### **Eyes**
* Miosis
* ↑ aqueous outflow → ↓ IOP
### **Heart**
* ↓ HR
* ↓ AV conduction
### **Respiratory**
* **Bronchoconstriction**
* ↑ secretions
### **GI**
* ↑ motility
* ↑ secretions
### **GU**
* ↑ detrusor contraction
* Relax sphincters → urination
### **Glands**
* Profuse sweating, lacrimation, salivation
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# **5. CONTRAINDICATIONS**
* **Asthma/COPD** (bronchospasm)
* **Peptic ulcer** (↑ acid)
* **Coronary artery disease / hypotension**
* **GI obstruction / urinary obstruction**
* Parkinsonism (for some agents)
* Hyperthyroidism (risk of arrhythmia)
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# **6. IMPORTANT DRUG–DRUG INTERACTIONS**
* β-blockers → severe bradycardia
* Anticholinergics → antagonize effect
* Depolarizing relaxants (succinylcholine) → prolonged paralysis
* TCA/antihistamine toxicity → physostigmine useful
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# **7. CHOLINERGIC TOXICITY (CLINICAL FEATURES)**
### **Muscarinic signs (DUMBBELSS)**
* Diarrhea
* Urination
* Miosis
* Bronchospasm
* Bradycardia
* Emesis
* Lacrimation
* Salivation
* Sweating
### **Nicotinic signs**
* Muscle fasciculations → paralysis
* Hypertension (early)
### **CNS**
* Anxiety → seizures → coma
### **Treatment**
* **Atropine + Pralidoxime + Diazepam**
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# **8. HIGH-YIELD EXAM POINTS**
* **Bethanechol → urinary retention**
* **Pilocarpine → acute glaucoma**
* **Physostigmine → antidote for atropine overdose**
* **Edrophonium → MG diagnosis**
* **Pyridostigmine → MG long term**
* **Organophosphate poisoning → treat with atropine first**
* **Cevimeline → Sjögren (M3 selective)**
---
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Below are **20 high-yield, exam-style, real-life–based case scenarios** on **Parasympathomimetic Drugs**.
Each scenario includes **presentation → analysis → final diagnosis / drug logic**.
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# **20 Case Scenarios – Parasympathomimetic Drugs**
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### **1. Postpartum urinary retention**
A 26-yo woman delivered 12 hours ago and has not voided since. Bladder scan shows 780 mL urine. No obstruction.
**Management:** Start **Bethanechol** to stimulate M3 → detrusor contraction → initiate urination.
**Reason:** Most appropriate parasympathomimetic for urinary retention.
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### **2. Neurogenic bladder after spinal injury**
A 32-yo man with spinal cord injury passes very small amounts of urine with incomplete emptying.
**Management:** **Bethanechol** for neurogenic atonic bladder.
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### **3. Myasthenia gravis – morning fatigability**
A 28-yo woman presents with ptosis worsening toward evening, improved after rest. Ice test positive.
**Best chronic drug:** **Pyridostigmine** (long acting AChE inhibitor).
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### **4. Myasthenic crisis vs cholinergic crisis**
A known MG patient develops sudden respiratory weakness. You need to differentiate cause.
**Test:** **Edrophonium test** (short-acting).
Improvement → **Myasthenic crisis**
Worsening → **Cholinergic crisis**
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### **5. Reversal of non-depolarizing muscle relaxant**
During surgery vecuronium was used. After the procedure, the patient has inadequate spontaneous breathing.
**Drug to reverse:** **Neostigmine + atropine**.
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### **6. Anticholinergic toxicity (atropine overdose)**
A child accidentally ingests atropine tablets: dilated pupils, flushing, hyperthermia, tachycardia, dry mucosa, delirium.
**Antidote:** **Physostigmine** (crosses BBB).
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### **7. Acute angle-closure glaucoma attack**
A 60-yo man presents with severe ocular pain, halos, fixed mid-dilated pupil, high IOP.
**Immediate drug:** **Pilocarpine** to produce miosis → opens angle → ↑ drainage.
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### **8. Sjögren syndrome – severe dry mouth**
A 52-yo woman has dry mouth, dental caries, difficulty swallowing dry food.
**Best drug:** **Cevimeline** or Pilocarpine (M3 agonists → ↑ salivation).
---
### **9. Alzheimer’s disease – mild cognitive decline**
A 70-yo male has progressive memory loss, MMSE 22/30.
**Next step:** Start **Donepezil / Rivastigmine** (central AChE inhibitors).
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### **10. Organophosphate poisoning – farmer**
A farmer exposed to pesticides presents with sweating, salivation, pinpoint pupils, vomiting, muscle fasciculations, wheezing, bradycardia.
**Management:**
1. **Atropine** IV (repeat till secretions dry)
2. **Pralidoxime (2-PAM)**
3. Diazepam for seizures.
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### **11. COPD patient mistakenly given pilocarpine**
A 70-yo COPD patient develops severe bronchospasm after using a “new eye drop.”
**Cause:** **Pilocarpine** can trigger bronchoconstriction → contraindicated in asthma/COPD.
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### **12. Post-operative ileus**
A 55-yo man after abdominal surgery has absent bowel sounds, abdominal distension.
**Management:** **Neostigmine** (stimulates peristalsis).
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### **13. Elderly with bradycardia after pyridostigmine**
A patient on pyridostigmine for MG develops dizziness, syncope, low pulse.
**Explanation:** Excessive cholinergic effect → bradycardia.
**Management:** Dose reduction or add atropine if severe.
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### **14. Nerve agent exposure in civilian**
Victim in subway with pinpoint pupils, frothy secretions, apnea, seizures → suspected sarin exposure.
**Management:**
* High-dose **Atropine**
* **Pralidoxime** ASAP
* Mechanical ventilation
* Diazepam
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### **15. Glaucoma patient sees black shadows after pilocarpine**
A patient complains of difficulty seeing in dark after starting pilocarpine.
**Cause:** Miosis reduces night vision.
---
### **16. Child with congenital megacolon (Hirschsprung)**
A child with chronic constipation is suspected to have functional obstruction.
**Avoid:** **Bethanechol** because obstruction must be ruled out (risk of perforation).
---
### **17. Elderly dementia patient with bradycardia after donepezil**
A 78-yo man on Donepezil for Alzheimer’s develops syncope and pulse 44 bpm.
**Next step:** Stop drug → donepezil can cause **severe bradycardia**.
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### **18. Woman with peptic ulcer – worsened symptoms**
A patient with PUD is started on bethanechol for urinary retention. She develops epigastric pain.
**Mechanism:** M3 activation → ↑ gastric acid secretion → worsens ulcer.
**Drug contraindicated**.
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### **19. Patient with asthma given neostigmine**
A patient with bowel pseudo-obstruction is given neostigmine and develops breathlessness.
**Reason:** Muscarinic agonism → bronchoconstriction.
---
### **20. Mushroom poisoning – muscarinic**
A 25-yo man eats mushrooms → severe abdominal cramps, salivation, sweating, diarrhea, bradycardia.
**Likely toxin:** **Muscarine** (direct muscarinic agonist).
**Treatment:** **Atropine**.
---
If you want, I can now generate:
✅ **20 Hard Case-Based MCQs**
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Below are **20 high-yield, clinically realistic case scenarios focusing ONLY on *side-effects* of parasympathomimetic drugs**.
Each case clearly shows: **drug → side-effect → mechanism → corrective action**.
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# **20 Case Scenarios – Side Effects of Parasympathomimetic Drugs**
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### **1. Bethanechol causing severe abdominal cramps**
A postpartum woman receives bethanechol for urinary retention. Within 30 minutes she develops **intense abdominal cramps + diarrhea**.
**Cause:** Excessive M3 stimulation → ↑ GI motility.
**Action:** Reduce dose / stop drug.
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### **2. Bethanechol causing bronchospasm in an asthmatic**
A 28-year-old asthmatic woman given bethanechol develops **wheezing and dyspnea**.
**Mechanism:** M3 stimulation → bronchoconstriction.
**Action:** Stop drug; give bronchodilators.
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### **3. Pilocarpine eye drops → headache + brow ache**
A glaucoma patient reports **frontal headache and brow pain** after pilocarpine drops.
**Reason:** Ciliary muscle spasm.
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### **4. Pilocarpine → excessive sweating**
A patient on oral pilocarpine for Sjögren syndrome develops **profuse sweating**.
**Mechanism:** M3 on sweat glands.
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### **5. Pilocarpine → worsened night vision**
A 62-yo patient reports **poor night vision** after pilocarpine.
**Reason:** Miosis → reduced light entry.
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### **6. Pilocarpine in COPD patient → acute bronchospasm**
A COPD patient given pilocarpine eye drops develops **severe breathlessness**.
**Mechanism:** Systemic absorption → bronchoconstriction.
**Contraindicated.**
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### **7. Neostigmine IV → bradycardia**
A 40-year-old male receiving neostigmine for ileus develops **pulse 42/min**.
**Reason:** Muscarinic activation of SA/AV nodes.
**Action:** Give **atropine**.
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### **8. Neostigmine → excessive salivation & diarrhea**
A patient on neostigmine for MG reports **profuse salivation, watery stool**.
**Mechanism:** Cholinergic excess.
**Action:** Reduce dose.
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### **9. Pyridostigmine overdose → muscle fasciculations**
MG patient starts self-increasing dose and develops **muscle twitching + weakness**.
**Reason:** Nicotinic receptor overactivation → depolarizing block (cholinergic crisis).
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### **10. Pyridostigmine → severe abdominal cramps**
A 32-year-old MG patient complains of **repeated abdominal cramping** after starting pyridostigmine.
**Mechanism:** ↑ GI motility due to M3 stimulation.
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### **11. Edrophonium test → worsening weakness**
During Tensilon test, patient develops **more muscle weakness + vomiting**.
**Interpretation:** **Cholinergic crisis** caused by edrophonium.
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### **12. Physostigmine → seizures**
A patient treated with physostigmine for atropine overdose develops **generalized seizures**.
**Reason:** CNS penetration → cholinergic overactivity in brain.
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### **13. Donepezil → syncope**
An elderly Alzheimer's patient on donepezil presents with **syncope + bradycardia (HR 46)**.
**Cause:** Vagal overstimulation.
**Action:** Stop drug.
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### **14. Rivastigmine patch → nausea and weight loss**
A 70-year-old on rivastigmine patch reports **persistent nausea, vomiting, weight loss**.
**Mechanism:** Muscarinic GI stimulation.
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### **15. Galantamine → urinary frequency**
Patient on galantamine develops **frequent urination + urgency**.
**Reason:** Increased detrusor contraction (M3 effect).
---
### **16. Echothiophate (irreversible AChE inhibitor) eye drops → cataract**
Long-term echothiophate use in glaucoma results in **iris pigmentation + thickened lens (cataract)**.
**Mechanism:** Chronic miosis → lens changes.
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### **17. Organophosphate exposure – pinpoint pupils**
A farmer exposed to parathion has **extreme miosis → blurred vision**, interfering with work.
**Mechanism:** Muscarinic overstimulation.
---
### **18. Organophosphate poisoning → bronchorrhea**
A patient develops **massive airway secretions** requiring suction.
**Mechanism:** M3 stimulation of glandular secretion.
---
### **19. Organophosphate toxicity → muscle paralysis**
Victim develops **progressive paralysis** after initial fasciculations.
**Mechanism:** Sustained nicotinic depolarization → paralysis.
---
### **20. Cevimeline → visual blurring**
A 52-yo Sjögren patient on cevimeline reports **difficulty focusing and blurry near vision**.
**Reason:** Ciliary muscle overcontraction (accommodation spasm).
---
If you want, I can continue with:
✅ **20 HARD MCQs (side-effects only)**
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✅ **Tags**
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