08 - Cholinoreceptor blockers

Question 1

Cholinoreceptor blocker types

Answer 1

anticholinergic drugs

• antimuscarinic
• –M1-selective (pirenzepine)
• –non-selective (atropine)
• antinicotinic
• –ganglion blockers (hexamethonium)
• –neuromuscular blockers (tubocurarine)

cholinesterase regenerators
- oximes (pralidoxime)

Question 2

ATROPINE
class
similar drug
MOA
uses
SE

Answer 2

• cholinergic antagonist (muscarinic)
• homatropine, cyclopentolate, tropicamide
• completely blocks ALL muscarinic receptors
  mydriatic, cyclopegic, antidote for organophosphate poisoning (first choice), bradycardia, hypersalivation
• tachycardia, mydriasis, cyclopegia, skin flushing, delirium, hallucinations

Question 3

BENZTROPINE
class
similar drug
MOA
uses
SE

Answer 3

• cholinergic antagonist (muscarinic)
• biperiden, trihexyphenidyl
• completely blocks all muscarinic receptors, restores neurotransmitter balance in the basal ganglia
• parkinson’s disease
• BOV, dry eyes, constipation, dry mouth, urinary retention

reduces tremors more than bradykinesia or rigidity

Question 4

Muscarinic antagonists for parkinsonism

Answer 4

trihexyphenidyl
benztropine
biperiden

Question 5

IPRATROPIUM
class
similar drug
MOA
uses
SE

Answer 5

• cholinergic antagonist (muscarinic)
• tiotropium
• blocks muscarinic receptors in bronchial smooth muscle, prevents vagal-stimulated bronchoconstriction
• asthma, COPD
• dry mouth, cough, nasal dryness

more effective and less toxic than beta-agonists in patients with COPD and heart disease

Question 6

SCOPOLAMINE
class
similar drug
MOA
uses
SE

Answer 6

• cholinergic antagonist (muscarinic)
• none
• completely blocks all muscarinic receptors, antagonizes histamine and serotonin
• motion sickness, decrease acid secretion in GIT
• drowsiness, BOV, dry eyes, constipation, dry mouth, urinary retention

applied as transdermal patch

Question 7

DICYLOMINE
class
similar drug
MOA
uses
SE

Answer 7

• cholinergic antagonist (muscarinic)
• hyoscyamine, glycopyrrolate
• completely blocks M3 receptors
• IBS, minor diarrhea, decrease acid secretion in GIT
• tachycardia, confusion, urinary retention, increased IOP

available PO and IV forms, relatively short t1/2 (6 hours)

Question 8

OXYBUTYNIN
class
similar drug
MOA
uses
SE

Answer 8

• cholinergic antagonist (muscarinic)
• darifenacin, solifenacin, tolteradine, trospium
• slightly blocks M3 receptors, reduces detrusor muscle tone
• urge incontinence, post-operative spasms
• tachycardia, constipation, xerostomia, increased IOP

Question 9

ATROPINE TOXICITY

Answer 9

atropine fever (hyperthermia)
atropine flush (cutaneous vasodilation)
decreased secretions
tachycardia
arrhythmias (intraventricular conduction block)
constipation
BOD
CNS toxicity

Question 10

Contraindications to muscarinic blockers

Answer 10

cautious use in infants - hyperthermia due to decreased sweating
acute angle closure glaucoma
BPH

Question 11

Ganglion blockers

Answer 11

competitive pharmacologic antagonists at nicotinic acetylcholine receptors
first successful agents for the treatment for hypertension but abandoned
adverse effects of ganglion blockade in hypertension are so severe

Question 12

HEXAMETHONIUM
class
similar drug
MOA
uses
SE

Answer 12

• cholinergic antagonist (nicotinic)
• trimethaphan
• competitively blocks Nn nicotinic ACh receptors
• hypertension (obsolete), hypertensive emergencies
• sympatholytic, orthostatic hypertension, sexual dysfunction, dry mouth, blurred vision, constipation

Question 13

Neuromuscular blockers

Answer 13

for complete skeletal muscle relaxation in surgery

Question 14

Neuromuscular blocker classification

Answer 14

• non depolarizing
• –tubocurarine, pancuronium, atracurium, vecuronium
• depolarizing
• –syccinylcholine