Pharmacology

Cholinergic Antagonist

Anti-cholinergic drug

  • Anticholinergics are those antagonize the effect of neurotransmitter (Ach) on autonomic effectors and in the CNS.
  • The parasympatholytic drugs are bind to the cholinoreceptor (Muscarinic and nicotinic) and prevent the effect of Ach.

classification

Atropine

  • Atropine sulphate is a tertiary amine (belladonna alkaloid).
  • It binds competitively at binding site of the Ach.
  • Atropine acts both centrally and peripherally.

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 center in the hypothalamus.

Local anaesthetic

  • Mild anaesthetic 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 ½ 3-4 hours.
  • Hyoscine is more completely metabolized and has better blood-brain barrier penetration.

Therapeutic uses

Anti-secretory

  • Pre-anesthetic medication: reduce excessive salivation and respiratory secretions.
  • Peptic Ulcer: decrease gastric secretion and provide symptomatic relief in peptic ulcer.

Anti-spasmodic

  • Gastritis, gastric hypermotility 
  • Bronchial asthma
  • As Mydriatics and Cycloplegia
  • Parkinsonism as an adjuvant to Levodopa.
  • Antagonize muscarinic effects of anticholinesterase (Mushroom poisoning)

Scopolamine

  • Tertiary amine (alkaloid).
  • Produce peripheral effect as well as CNS effects.
  • Peripheral effect similar to Atropine, but greater action on CNS (longer action as compare to Atropine).

Action

  • Effective anti-motion sickness.
  • Produce sedation (higher dose) and excitement.
  • Euphoria (state of intense excitement and happiness)

Therapeutic uses

  • Motion sickness
  • Postoperative nausea and vomiting

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. Presently I am working as an Assistant Professor at The pharmaceutical college, Barpali.

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