Parasympatholytic Drugs

• Parasympatholytic Drugs block acetylcholine action in the parasympathetic system, reducing secretions, relaxing smooth muscles, and increasing heart rate (Also called Anticholinergics or Cholinergic Antagonists)

Definition of Parasympatholytic Drugs:

• These drugs block the effects of the parasympathetic nervous system by inhibiting acetylcholine at muscarinic receptors.

Examples of Parasympatholytic Drugs:

• Atropine – prototype drug
• Scopolamine – used for motion sickness
• Ipratropium bromide – used in asthma and COPD
• Oxybutynin – used in overactive bladder

Mechanism:

• Competitive inhibition of muscarinic receptors (e.g., atropine, scopolamine)

Pharmacological Effects:

1. Eye

   • Mydriasis (pupil dilation): Relaxation of sphincter muscle.
   • Cycloplegia: Paralysis of accommodation → blurred near vision.
   • Risk of acute angle-closure glaucoma in predisposed patients.

2. Cardiovascular System

   • Tachycardia: Blockade of M2 receptors at SA node → increased heart rate.
   • Little direct effect on blood pressure.

3. Respiratory System

   • Bronchodilation: Blocking M3 receptors on bronchial smooth muscle.
   • Decreased secretions: Dry airway and reduced mucous.

4. Gastrointestinal Tract

   • Reduced motility and tone: Antispasmodic effect (useful in IBS).
   • Decreased secretions: Dry mouth (xerostomia), constipation, delayed gastric emptying.

5. Urinary Tract

   • Relaxation of detrusor muscle: Reduces urgency, frequency (used in overactive bladder).
   • Increased internal sphincter tone: Leads to urinary retention.

6. Glands

   • Dry mouth, dry eyes, dry skin: Due to suppressed secretions.

Effects:

• Increased heart rate
• Decreased gland secretion
• Bronchodilation
• Decreased GI motility and urinary retention
• Pupil dilation (mydriasis)

Clinical Uses:

• Bradycardia
• Pre-anesthetic to reduce secretions
• Motion sickness (Scopolamine)
• COPD/asthma (Ipratropium, Tiotropium)
• Overactive bladder
• Mydriasis induction for eye examination

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