Cholinoceptor-Blocking Drugs

• Introduction:

These drugs are classified as Anti-Muscarinic and Anti- Nicotinic drugs. Anti-nicotinic drugs are ganglion blockers and neuromuscular junction blockers. The ganglion blockers have a very little clinical use.

Muscarinic Receptor Antagonists/ Muscarinic Receptor Blockers

• Antimuscarinic agents were of plant origin.

• Belladonna (beautiful woman, a reference to the drug's mydriatic effects,) are found in many plants.

• Atropa belladonna (Solanaceae) or the deadly nightshade contains atropine (dl-hyoscyamine) as does Datura stramonium (Jamestown or jimsonweed, thorn-apple, etc.)

• Scopolamine, also an alkaloid, is found in the shrub Hyosyamus niger and Scopolia carniolica.

  • An alkaloid is one of a large group of organic, basic plant substances. They are usually pharmacologically active and bitter in taste

  • Alkaloids

    • atropine

    • caffeine

    • morphine

    • nicotine

    • quinine

    • strychnine

• Tertiary and Quaternary Antimuscarinic Agents

  • Tertiary amines: Eg Atropine, scopolamine, homatropine, Pirenzepine, Benztropine, are, generally well-absorbed and able to penetrate the CNS.

  • Quaternary muscarinic receptor antagonists: Eg-, Ipratropium, Glycopyrolate etc - tend to be more potent as muscarinic blockers and have increased ganglionic blocking action.

  • Quaternary (permanently charged) antagonists do not penetrate the CNS to a significant extent. Therefore, CNS activity is limited.

Category: Pharmacology Notes