Flashcards in CHOLINOCEPTOR-BLOCKING DRUGS Deck (44):
1
MUSCARINIC ANTAGONISTS
Selective
Only a few receptor-selective
--- antagonists have reached clinical trial
Pirenzipine
M1
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MUSCARINIC ANTAGONISTS
A. CLASSIFICATION AND PHARMACOKINETICS
Subdivided into
Most of the drugs in the market
2. Nonselective
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Cholinoreceptor antagotists are divided into two:
-Muscarinic, blocks parasympathetic autonomic discharge. Atropine is the prototype of these drugs.
-Nicotinic, competitively block the actions of acetylcholine at nicotinic receptors of both parasympathetic and sympathetic ganglia.
MUSCARINIC
NICOTINIC
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Cholinoreceptor antagotists are divided into two:
blocks parasympathetic autonomic discharge. Atropine is the prototype of these drugs.
Muscarinic
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Cholinoreceptor antagotists are divided into two:
competitively block the actions of acetylcholine at nicotinic receptors of both parasympathetic and sympathetic ganglia.
Nicotinic
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Prototype nonselective muscarinic
blocker
Derivative of a deadly night shade
Atropa belladona and other plants
ATROPINE
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Tertiary amine
Relatively lipid soluble
Crosses membrane barriers
Well distributed in the CNS and other
organs
ATROPINE
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Eliminated partially by metabolism in
the liver
Partially by renal excretion
Elimination half-life is 2 hours
ATROPINE
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Duration of action of normal doses is
4-8 hours in all organs
For the eye, it last for 72 hours
Salivary or bronchial glands are
sensitive to the effect of atropine
ATROPINE
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organ affected by muscarinic antagonists
Sedation, hallucination, drowsiness, antimotion sickness action, antiparkinson action, amnesia
CNS
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organ affected by muscarinic antagonists
Mydriasis, cyclopegia, lacrimal glands become dry and sandy
eye
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organ affected by muscarinic antagonists
Initial bradycardia at low doses then tachycardia
heart
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organ affected by muscarinic antagonists
Bronchodilation, decrease in bronchial secretions
Respiratory
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organ affected by muscarinic antagonists
Relaxation, decrease motility, antidiarrheal, prolongs gastric
emptying time
GIT
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organ affected by muscarinic antagonists
Relaxation of the bladder wall, urinary retention
gut
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organ affected by muscarinic antagonists
Decrease secretion, salivation, lacrimation, sweating
gland
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organ affected by muscarinic antagonists
None
skeletal muscle
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EFFECTS OF INCREASING DOSE OF
ATROPINE
(7)
Decrease bronchial and salivary
secretions
Decrease sweating
Mydriasis
Tachycardia
Urinary hesitancy
Decrease intestinal motility
Decrease gastric secretion
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MUSCARINIC ANTAGONISTS
D. CLINICAL USES
1. CNS
Parkinson’s disease
Decrease dopamine and cholinergic
transmission
Benztrypine, biperiden,
trihexyphenidyl
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MUSCARINIC ANTAGONISTS
D. CLINICAL USES
2. EYE
Used to dilate the pupil
Paralyze accommodation
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D. CLINICAL USES
1. CNS
Widely distributed
Excreted rapidly
Standard therapy for motion sickness
Dicyclomine
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Used to reduce airway secretions
during general anesthesia
IV atropine
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Quaternary antimuscarinic agent
Used by inhalation
Promote bronchodilation
Asthma and COPD
Ipratropium
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Used for peptic ulcer
M1-selective inhibitor pirenzipine
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Used to reduce acid secretion
Not as effective as the H
2 antagonists
Atropine
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MUSCARINIC ANTAGONISTS
D. CLINICAL USES
5. GUT
Used to reduce urgency in mild cystitis
Used to reduce bladder spasm following
urologic surgery
Treatment of enuresis
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MUSCARINIC ANTAGONISTS
D. CLINICAL USES
6. CHOLINERGIC POISONING
Antidote for organophosphate insecticide poisoning
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Blockade of thermoregulatory
sweating
Can result to hyperthermia
“Atropine fever”
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Dilation of the cutaneous vessels
of the arm, head, neck and trunk
“Atropine flush”
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NICOTINIC ANTAGONISTS
A. CLASSIFICATION
Subdivided into
Act like competitive pharmacologic
antagonists
First successful agents for the treatment
of hypertension
1. GANGLION-BLOCKING DRUGS
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1. GANGLION-BLOCKING DRUGS
Tetraethylammonium, hexamethonium
Mecamylamine (increase oral absorption)
Trimethaphan (hypertensive emergencies)
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NICOTINIC ANTAGONISTS
A. CLASSIFICATION
Adverse effects in hypertension are so
severe
Both sympathetic and parasympathetic
are blocked
1. GANGLION-BLOCKING DRUGS
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1. GANGLION-BLOCKING DRUGS
Adverse effects
Dry mouth
Blurred vision
Severe sexual dysfunction
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NICOTINIC ANTAGONISTS
A. CLASSIFICATION
Important for producing complete
muscle skeletal relaxation in surgery
Classified into two
2. NEUROMUSCULAR-BLOCKING DRUGS
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NEUROMUSCULAR-BLOCKING DRUGS
Tubocurarine is the prototype
Competitive block at the end plate
nicotinic receptor
a. NONDEPOLARIZING GROUP
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NEUROMUSCULAR-BLOCKING DRUGS
Causes flaccid paralysis
Last for 30-60 minutes
Pancuronium, atracurium, vecuronium
a. NONDEPOLARIZING GROUP
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NEUROMUSCULAR-BLOCKING DRUGS
Nicotinic agonists not antagonists that
cause flaccid paralysis
Succinylcholine is the only member
b. DEPOLARIZING GROUP
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effect of nicotinic antagonists on the CNS
Sedation, tremor
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effect of nicotinic antagonists on the EYE
Mydriasis and cycloplegia
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effect of nicotinic antagonists on the GIT
Marked reduced motility, constipation
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effect of nicotinic antagonists on the GUT
Reduced contractility of the bladder, urinary
hesitancy, impairment of erection and ejaculation
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effect of nicotinic antagonists on the HEART
Vasodilator, antihypertensive, tachycardia
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effect of nicotinic antagonists on the BLOOD VESSELS
Reduction in arteriolar and venous tone, BP decrease,
orthostatic hypotension
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