Anticholinergic Drugs
Content
ANS
•
Anticholinergic
drugs
•
Pharmacology
of atropine
•
Atropine
poisoning and its treatment
At the
end of this lecture, student will be able to
• List
the anticholinergic drugs
• Explain
the pharmacology of atropine
• Explain
atropine poisoning and its treatment
Anticholinergic drugs (Parasympatholytics)
Muscarinic Receptor Blockers
• Atropine
& related alkaloids from Atropa
belladonna
Belladonna Alkaloids
• Atropine
(dl – hyoscyamine)
– Ester
of tropic acid + Tropine
• Scopolamine
(Hyoscine)
– Ester
of tropic acid + Scopine
MOA of
Atropine
• Block
peripheral and central effects of Ach
• Competitive
antagonism
• Dose
for M blockade varies from organ to organ
• Salivary,
bronchial secretion – extremely sensitive
• Vagal
stimulation: Not completely abolished
• Large
doses: NN Blockade
Differences
between Atropine and Scopolamine
|
Atropine |
Scopolamine |
|
CNS stimulation |
CNS depression |
|
More active on heart, gut, bronchial smooth muscle |
Prominent effects on iris, ciliary body, salivary, |
|
Longer duration |
Shorter |
Pharmacological actions of Atropine
• Secretion:
Decreases (except milk)
• Salivary:
Dryness of mouth, difficulty in swallowing
• Gastric:
Decrease volume and acidity, mucous and gastric enzymes
• Other
secretions:
– Bronchial
secretions become viscid
– Inhibits
sweat secretion
– Not
significant on lacrimal secretion
Pharmacological actions of Atropine on smooth muscle
• GIT:
Decreases tone and motility, Antispasmodic
• Biliary
tract: Weak antispasmodic
• Urinary
tract: Decreases ureteral peristalsis, urinary retention
• Bronchi:
Relax bronchi and bronchioles, dries up secretion
• Uterus:
No significant effect
Pharmacological actions of Atropine on eye
• Mydriasis
(Blocks cholinergic nerves of sphincter if iris)
• Photophobia
(Sphincter paralysis)
• Ciliary
smooth muscle paralysis – cycloplegia
• No
changes in i.o.t in normal individuals
• In
narrow angle glaucoma: increases
• Due
to relaxation of ciliary muscle and crowding of iris
Pharmacological Actions of Atropine on CVS
CVS
• Initially
decreases HR – ++ of vagal nuclei
• Tachycardia:
X of M2 R in SA node
• Counters
the vasodilation and hypotension of cholinergic agents
• Toxic
dose: Dilation of cutaneous blood vessels – atropine flush+ hypotension
Pharmacological Actions of Acetylcholine on CNS
Atropine
• Mild + of medullary vagal nuclei & higher
cerebral centers
• Produces
bradycardia and increase rate, depth of respiration
Scopolamine
• Depress
RAS
• Euphoria,
drowsiness, amnesia, dreamless sleep
• Motion
sickness (Vestibular function)
ADME
• All
route: Satisfactory absorption
• From
eye, intact skin: Not significant
• Partly
detoxified by liver, partly unchanged
• Cross
placental barrier, sec in milk and saliva
• Excreted
through urine
ADR
• Infants,
children – CNS toxicity
• Elderly
– Glaucoma, urinary retension
• Locally
– Allergic dermatitis, conjunctivitis,
swelling of eyelids
• Mild
– Xerostomia, flushing, constipation
• Acute
atropine poisoning
• Children:
10-20 mg, Adults: 80 – 130 mg
• Wide
margin of safety
Acute Atropine Poisoning
Peripheral blockade
• Dry
mouth, difficulty in swallowing, intense thirst
• Tachycardia,
palpitation, flushing
• Hyperpyrexia
• Dilation
of pupils, blurred vision, photophobia
• Urinary
urgency, difficulty in micturition, urinary retention
• Rash
– Face, neck, upper part of trunk
Acute Atropine Poisoning – Mydriasis
Central effects
• Initial
stimulation subsequent depression
• Excitement,
restlessness, motor in co-ordination
• Slurring
of speech
• Disturbance
of memory, confusion, hallucination
• Severe
poisoning: Depress vasomotor centre
Treatment of Atropine poisoning
• Gastric
lavage
• Universal
antidote
• Slow
IV – physostigmine (1 – 4 mg) – cross BBB
• SC
– neostigmine (2-5mg)
• Restlessness,
delirium – Diazepam
• Darkroom
– photophobia
• Catheter
– for urinary retention
• Tepid
sponging – pyrexia
Therapeutic uses
• Gastrointestinal
colic
• Ocular
conditions
• Preanesthetic
medication
• OPC
poisoning
• PD
• To
abolish AV block
• Urinary
incontinence
• Motion
sickness
Contraindications
• With
caution: above 40 years (Acute angle glaucoma)
• Enlarged
prostate – urinary retention
• Chronic
lung diseases
• CHF
with tachycardia
Summary
• Block
peripheral and central effects of Ach
• Atropine
(dl – hyoscyamine)
– Ester
of tropic acid + Tropine
– Mild stimulation of medullary vagal nuclei &
higher cerebral centers
• Scopolamine
(Hyoscine)
– Ester
of tropic acid + Scopine
– Depress
RAS
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