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Antihistaminic Agents (Med Chem: 2) Notes Download

Keywords: Download PDF, Notes, PPT, Antihistaminic Agents, Histamine, H1-Antihistamines, H2-Antihistamines, First Generation Antihistamines, Second Generation Antihistamines, Histamine Receptors, Diphenhydramine, Dimenhydrinate, Clemastine Fumarate, Chlorpheniramine Maleate, Cimetidine, Famotidine, Ranitidine

This document provides detailed notes on antihistaminic agents, including their classification, mechanisms of action, and therapeutic uses. It also covers the synthesis and properties of various antihistaminic drugs.

Antihistaminic Agents (Med Chem: 2) Notes

Introduction

Histamine, a biologically active substance, potentiates the inflammatory and immune responses of the body. It also regulates physiological functions in the gut and acts as a neurotransmitter. Antihistaminic agents (or histamine antagonists) are drugs that antagonize the action of histamine. Based on the type of H receptor targeted, antihistamines are divided into:

• H1-Antihistamines: Used for treating allergic reactions and disorders mediated by mast cells. They are subdivided into two generations. First-generation H1-antihistamines have central effects and are used as sedatives. Second-generation H1-antihistamines have low central effects and are used as anti-allergenic drugs.
• H2-Antihistamines: Reduce the production of stomach acid by reversibly blocking H2-histamine receptors found in the parietal cells of gastric mucosa. They are used in gastric reflux diseases.

Histamine

Histamines are nitrogen-containing organic compounds belonging to the group of amines. They are produced in almost all cells during a local immune response and regulate various physiological functions of the gut. Histamines also play a role in neurotransmission. They are synthesized and released by basophils and mast cells on stimulation, initiating inflammatory responses by increasing vascular permeability for white blood cells and proteins.

Summary of Key Points

1. Histamine potentiates inflammatory and immune responses.
2. Antihistaminic agents antagonize the action of histamine.
3. First-generation H1-antihistamines have central effects and are used as sedatives.
4. Second-generation H1-antihistamines have low central effects and are used as anti-allergenic drugs.
5. Histamines are nitrogen-containing organic compounds.
6. Histamines are synthesized and released by basophils and mast cells.
7. Diphenhydramine is a first-generation antihistamine used for seasonal allergies.
8. Dimenhydrinate is a combination drug containing diphenhydramine and 8-chlorotheophylline.
9. Clemastine fumarate is an antihistamine with antimuscarinic and sedative properties.
10. Diphenylpyraline is an antihistamine used for treating allergies.
11. Tripelennamine is an ethylenediamine derivative with antihistaminergic properties.
12. Chlorcyclizine is a first-generation antihistamine of the phenylpiperazine class.
13. Meclizine hydrochloride is a synthetic piperazine with antiemetic and sedative properties.
14. Buclizine hydrochloride is a piperazine H1-receptor antagonist with antiemetic and anti-vertigo properties.
15. Chlorpheniramine maleate is an H1-receptor antagonist.
16. Triprolidine hydrochloride is obtained by reacting triprolidine with hydrogen chloride.
17. Phenindamine tartrate is a phenylalkylamine sympathomimetic amine.
18. Promethazine hydrochloride is a phenothiazine derivative with antihistaminic, sedative, and antiemetic properties.
19. Trimeprazine tartrate is a phenothiazine derivative used as an antipruritic agent.
20. Cyproheptadine is a first-generation antihistamine used as an appetite stimulant and for treating allergic rhinitis and urticaria.
21. Azatadine maleate is a first-generation antihistamine.
22. Astemizole is a long-acting, non-sedating second-generation antihistamine.
23. Loratadine is a second-generation H1-receptor antagonist.
24. Cetirizine is an orally active second-generation H1-antagonist.
25. Levocetirizine is a third-generation non-sedative antihistamine.
26. Cromolyn sodium is a mast cell stabilizer with anti-inflammatory activity.
27. Cimetidine is a histamine congener that competitively inhibits H2-receptors.
28. Famotidine is a competitive H2-receptor antagonist that inhibits gastric secretion.
29. Ranitidine is a non-imidazole blocker of H2-receptors that mediate gastric secretion.

Exercises

True or False

1. Histamine potentiates inflammatory and immune responses. (True)
2. First-generation antihistamines are used as hypnotics. (False)
3. Second-generation H1-antihistamines are used as sedatives. (False)
4. Histamines are nitrogen-containing organic compounds. (True)
5. Diphenhydramine is used for seasonal allergies. (True)
6. Chlorcyclizine is a second-generation antihistamine. (False)
7. Buclizine hydrochloride is an H2-receptor antagonist. (False)
8. Chlorpheniramine maleate is an H1-receptor antagonist. (True)
9. Cimetidine inhibits H2-receptors. (True)

Fill in the Blanks

1. Antihistaminic agents antagonize the action of ________. (Histamine)
2. Histamines are synthesized and released by _______ and ________. (Basophils, Mast Cells)

Very Short Answer Type Questions

1. Give the structure of histamine.
2. What are the types of histamine receptors?
3. Give the structure of diphenhydramine.
4. What is the mechanism of action of clemastine fumarate?
5. Enlist uses of doxylamine succinate.
6. Give the mechanism of action of levocetirizine.

Short Answer Type Questions

1. Write a short note on histamine.
2. Explain histamine receptors and their distribution in the body.
3. Write a note on recent developments in antihistaminic agents.
4. Give the synthesis of cimetidine.
5. Write a short note on ranitidine.

Long Answer Type Questions

1. Explain H1-antagonists and give the mechanism of action, uses, and structure of the following drugs:
   • Doxylamine succinate
   • Clemastine fumarate
   • Meclizine hydrochloride
   • Chlorpheniramine
   • Levocetirizine
2. Explain antihistaminic agents in detail and give their SAR.
3. Write about H2-antagonists in detail and the mechanism of action, uses of the following drugs:
   • Cimetidine
   • Famotidine
   • Ranitidine

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