CHOLINOCEPTOR-BLOCKING DRUGS Flashcards Preview

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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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effect of nicotinic antagonists on the GLANDS

Reduction in salivation, lacrimation, sweating and
gastric secretion

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