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

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

Frequently Asked Questions

1. Are all anticholinergic drugs associated with cognitive decline?
   • Understanding the nuances of cognitive effects.
2. Can anticholinergic medications be stopped abruptly?
   • Exploring the challenges and recommended withdrawal strategies.
3. What are some natural alternatives to anticholinergic drugs?
   • Exploring lifestyle changes and natural remedies.
4. How do regulatory guidelines ensure the safety of anticholinergic prescriptions?
   • Understanding the role of regulations in healthcare.
5. Where can I find more resources on anticholinergic drug research?
   • Exploring reliable sources for up-to-date information.

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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