MOA of Buscopan

Mechanism of Action of Buscopan (Hyoscine Butylbromide)

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Introduction

Buscopan (Hyoscine Butylbromide) is an antispasmodic drug widely used to relieve smooth muscle spasms in the gastrointestinal tract, biliary tract, urinary tract, and female reproductive system. It is commonly used for abdominal cramps, renal colic, biliary colic, irritable bowel syndrome (IBS), and dysmenorrhea.

The Mechanism of Action of Buscopan is primarily based on peripheral anticholinergic (muscarinic receptor–blocking) activity, which reduces smooth muscle contraction and alleviates spasms.

Mechanism of action of Buscopan
Buscopan antispasmodic mechanism
Stepwise mechanism of action of Buscopan
Buscopan MOA Flowchart

Mechanism of Action (Step-wise)

1. Competitive Antagonism of Muscarinic (M1–M5) Receptors – Primary Mechanism

Buscopan blocks muscarinic receptors, mainly M3 receptors located on smooth muscle cells in:

  • GI tract
  • Biliary tract
  • Urinary tract
  • Uterus

By blocking acetylcholine at these receptors, it prevents:

  • Smooth muscle contraction
  • GI motility increases
  • Spasmodic pain

Effect: Smooth muscle relaxation and spasm relief.

2. Poor CNS Penetration

Buscopan is a quaternary ammonium compound, meaning:

  • Does not cross the blood–brain barrier
  • Minimal central anticholinergic effects
  • Mainly acts peripherally

This makes it safer than atropine-like drugs.

3. Reduced GI Motility and Secretions

Muscarinic antagonism leads to:

  • ↓ Peristalsis
  • ↓ Intestinal spasms
  • ↓ GI secretions
  • ↓ Colicky pain

Useful in conditions like IBS and spastic dysmenorrhea.

4. Relief of Smooth Muscle Spasm in Urinary and Biliary Tracts

M3 receptors regulate contraction in:

  • Ureter
  • Bladder
  • Bile ducts
  • Gallbladder

Blocking these receptors provides relief in:

  • Renal colic
  • Biliary colic
  • Ureteric spasm

5. Summary of Mechanism

MechanismEffect
M3 receptor blockadeSmooth muscle relaxation
↓ Acetylcholine effectsLess spasm & pain
Peripheral-only actionNo central effects
↓ GI motilityRelief in IBS & cramps

Pharmacokinetics

  • Absorption: Incomplete oral absorption
  • CNS penetration: Minimal
  • Onset: Within 20–30 minutes
  • Duration: 4–6 hours
  • Metabolism: Hepatic
  • Excretion: Renal and fecal

Clinical Uses

  • Abdominal cramps
  • Irritable bowel syndrome (IBS)
  • Biliary colic
  • Renal colic (adjunct)
  • Dysmenorrhea
  • Spastic conditions of GI/urinary tracts
  • Diagnostic procedures (endoscopy/colonoscopy) for smooth muscle relaxation

Adverse Effects

  • Dry mouth
  • Constipation
  • Blurred vision
  • Tachycardia
  • Urinary retention
  • Flushing
  • Allergic reactions (rare)

Due to peripheral action, central effects like confusion or sedation are rare.

Contraindications

  • Myasthenia gravis
  • Megacolon
  • Narrow-angle glaucoma
  • Prostate hypertrophy (caution)
  • Obstructive uropathy

Comparative Analysis

FeatureBuscopanAtropineDicyclomine
CNS effectsMinimalHighModerate
GI spasm reliefStrongModerateStrong
Use in colicVery effectiveModerateLimited
DurationModerateLongModerate

MCQs

1. Buscopan relieves abdominal cramps by blocking:
a) Beta receptors
b) Muscarinic M3 receptors
c) Histamine receptors
d) Serotonin receptors
Answer: b) Muscarinic M3 receptors

2. Buscopan causes minimal central side effects because it:
a) Is not metabolized
b) Is a quaternary ammonium compound
c) Has high lipid solubility
d) Stimulates dopamine receptors
Answer: b) Is a quaternary ammonium compound

3. One main therapeutic use of Buscopan is:
a) Asthma
b) Renal and biliary colic
c) Hypertension
d) Depression
Answer: b) Renal and biliary colic

4. Buscopan decreases abdominal spasm by:
a) Increasing peristalsis
b) Blocking acetylcholine effects
c) Stimulating GI secretion
d) Blocking H2 receptors
Answer: b) Blocking acetylcholine effects

5. A common adverse effect of Buscopan is:
a) Hyperhidrosis
b) Dry mouth
c) Bradycardia
d) Sedation
Answer: b) Dry mouth

FAQs

Q1. Does Buscopan cause drowsiness?
No—minimal CNS penetration prevents sedation.

Q2. Can Buscopan be used for IBS?
Yes—effective for crampy abdominal pain associated with IBS.

Q3. Is Buscopan addictive?
No—it has no dependence potential.

Q4. Can Buscopan help in kidney stone pain?
Yes—it relieves ureteric spasms, improving symptoms.

Q5. Is Buscopan safe in pregnancy?
Generally considered safe, but use only under medical advice.

References

Goodman & Gilman’s Pharmacological Basis of Therapeutics
https://accesspharmacy.mhmedical.com/book.aspx?bookid=2189

Katzung: Basic and Clinical Pharmacology
https://accessmedicine.mhmedical.com/book.aspx?bookid=2464

Tripathi: Essentials of Medical Pharmacology
https://jaypeebrothers.com/

Harrison’s Principles of Internal Medicine
https://accessmedicine.mhmedical.com/book.aspx?bookid=2129

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