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: N_N 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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