Anticholinergic Drugs – Pharmacology B. Pharma 5th Semester PDF Notes

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,
bronchial, sweat secretion

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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