Therapeutic Uses of Cholinergic Receptor Blockers

• Pre-anesthetic medication – inhibit mouth, bronchial, and pharyngeal secretion which reduce reflex laryngospasm during general anesthesia.

• Management of intra-operative bradycardia.

• Use in antagonism of nondepolarizing neuromuscular-blocking agents

2. Central Nervous System Uses

• Antimuscarinics are used clinically as preanesthetic medication to reduce vagal effects secondary to visceral manipulation during surgery.

• Centrally acting antimuscarinics like benztropine, benzhexol etc are used in Parkinson's disease & in treating extrapyramidal side effects induced by antipsychotic drugs.

• Scopolamine (transdermal) is effective in preventing motion sickness.

• Atropine is an effective specific antidote to excessive cholinergic stimulation following organophosphate intoxication.

• By blocking muscarinic receptors, the consequence of cholinesterase inhibition is attentuated.

• Atropine may be used in conjunction with Pralidoxime which may reactivate phosphorylated & inhibited acetylcholinesterase.
  

• Treatment of Reflex-Mediated Bradycardia
• Anticholinergic drugs: drugs of choice for management of intraoperative bradycardia --especially if due to increased vagal tone
  
• Correction of Heart Block – 1^st, 2^nd & 3^rd Degree AV Block
  

4. Respiratory Uses

Bronchial Asthma

• Bronchodilation following anticholinergic drug administration is due to blockade of acetylcholine effects on airway smooth muscle muscarinic receptors-M3

• Preferred Route of Administration for bronchodilation: aerosol

• most effective in preventing/treating bronchospasm due to ß-adrenergic antagonists

• Ipratropium - synthetic quaternary ammonium atropine congener is the drug most commonly used for aerosol administration --

  • more effective than ß-adrenergic agonists in producing bronchodilation in patients with chronic bronchitis or emphysema (high cholinergic tone)

• Ipratropium has an advantage in asthma compared to atropine because:

  • Ipratropium does not inhibit mucociliary clearance (atropine does)

  • Ipratropium has no significant CNS effects.

5. Gastrointestinal Tract

• Vagal input affects gastrin release and may be blocked by atropine; however, gastric acid release is more effectively prevented by M₁ specific antimuscarinic drugs (pirenzapine) and H₂-selective histamine receptor blockers.

• Combined with Opioid antidiarrhoeal in traveller’s diarrhea.

6. Eye Disorders

• Opthalmoscopic examination of the retina –

  • Short acting drugs (Tropicamide, Cyclopentolate) prefered over atropine

  • Cyclopentolate –prefered in children

• To prevent adhesion formation in uveitis & iritis

7. Urinary Disorders

   • Provide symptomatic relief in the treatment of urinary urgency –inflammatory bladder disorders

   • Helps in reducing involuntary voiding in patients with neurologic diseases

8. Cholinergic drug poisoning

• Irreversible Anticholinesterase compounds poisoning either accidental or suicidal

  • Atropine 2mg every 5-15min till signs of atropinization –

  • Enzyme reactivator – like Pralidoxime are used to reactivate the enzyme acetylcholinesterase.

• Cholinergic Blockers:Adverse effects

  • Dry mouth (xerostromia), Blurred vision (cycloplegia), Photophobia (mydriasis), Tachycardia,

Category: Pharmacology Notes