Pharmacology

Anticholinergic drug

Anticholinergic drug

  • Anticholinergics are those antagonize the effect of neurotransmitter (Ach) on autonomic effectors and in the CNS.

Classification

  1. Natural alkaloid

e.g. Atropine, Hyoscine (Scopolamine)

  • Semisynthetic derivatives

e.g. Homatropine, Atropine Methonitrate, Hyoscine butyl bromide, Ipratropium bromide, Tiotropium bromide

  • Synthetic derivatives

A. Mydriatics: e.g. Cyclopentolate, Tropicamide

B. Quaternary Compound: e.g. Propantheline, Oxyphenonium, Clidinum, Pipenzolate, Methylbromide, Isopropamide, Glycopyrolate.

C. Tertiary amine: e.g. Dicyclomine, Valethamate, Pirenzepine.

D. Vasicoselective: e.g. Oxybutynin, Flavoxate, Tolterodine.

E. Anti-parkinsonian: e.g. Bipiridine, Procyclidine, Trihexyphenidyl (Benzhexol)

Mechanism of action

  • Anticholinergics are the class of drugs that blocks the neurotransmitter (Ach) in CNS and PNS.
  • It combine reversibly with muscarinic cholinergic receptor thus preventing access of neurotransmitter (Ach) in these sites.

Atropine

  • Atropine sulphate is a tertiary amine.
  • Administered i.v./i.m. in a range of 0.01-0.02mg/kg up to 0.4-0.6mg (Adult dose)
  • Cardiac vagal nerve is completely blocked with larger dose (severe bradycardia).

Pharmacological action

  • CNS
    • It shows CNS stimulant action, but not appropriate at low dose.
    • Stimulate many medullary centres, vagal respiratory, vasomotor (controlling the internal diameter of blood volume).
    • In high dose causes: Cortical excitation, Restlessness, Disorientation (A state of mental confusion), Hallucination and delirium (mental confusion).
  • CVS
    • Tachycardia (Most prominent), due to blockade of M2 receptor at SA node.
  • Eye
    • Topical ingestion of Atropine causes Mydriasis (Paralysis of sphincter pupillae).
    • Paralysis of Accommodation (Cycloplegia)
    • Increase in IOP.
  • Smooth muscle
    • GIT relaxation: Mediated by M3 blockade.
    • Contraction of stomach and intestine is reduced leads to constipation.
    • Bronchodilation: Especially COPD and Asthma patient.
    • Also antagonizes histamine, prostaglandin, leukotrienes, mediated vagal over activity.
    • Relaxation of ureter and bladder.
  • Glands
    • Atropine markedly decrease sweat, salivary tracheobronchial and lacrimal secretion by M3 blockade.
    • Skin and eyes becomes dry, talking and swallowing may be difficult.
  • Body temperature
    • Increase temperature, due to inhibition of sweating as well as stimulation of temperature regulating centre in the hypothalamus.
  • Local anesthetic
    • Mild anesthetic action on the cornea.
    • Sensitive to different organs and tissue: saliva, sweat, bronchial smooth muscle, heart smooth muscle, intestine, GIT.

Pharmacokinetics

  • Rapidly absorbed from g.i.t.
  • Freely penetrate cornea.
  • Crosses BBB is somewhat restricted.
  • About 50% metabolized in liver.
  • Excreted unchanged in urine.
  • t Ā½ 3-4 hours.
  • Hyoscine is more completely metabolized and has better blood-brain barrier penetration.

Hello! My name is Smrutiranjan Dash, a pharmacy professional. belonging from, Bargarh, Odisha. I have acquired Master degree in Pharmacy (Pharmacology) form B.P.U.T, Rourkela, Odisha. Currently I am working as an Assistant Professor at The pharmaceutical college, Barpali.

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