Medicinal chemistry-II - B.Pharm V semester - Histamine and its receptors ,antihistamine drugs

1. Swathi Pharma Jnan
By
Kencha swathi
Assistant professor
Bangalore

2.  Histamine is composed of an imidazole heterocyclic
compound and ethylamine side chain.
 Histamine plays an important role in human physiology
including regulation of the CVS,smooth muscle,exocrine
glands,immune system & centre nerve function.
Swathi Pharma Jnan

3.  Histamine is biosynthesized in Golgi apparatus of
storage cells ,mast cells & basophils.
 L-Histidine decarboxylase

 Pyridoxal phosphate(-CO₂)
(L-Histidine) (Histamine)
Swathi Pharma Jnan

4.  Histamine is found in all the tissues.
 Mast cells contain high concentration of histamine.
 Histamine is release during hypersensitivity reactions
by interaction of an antigen-IgE complex
Swathi Pharma Jnan

5.  Histamine receptors are designated as H₁ ,H₂,H₃ & H₄.
H₁ Receptor
Location: CNS neurons,Smooth muscle of respiratory
system,GIT,Uterine tissues,epithelial & endothelial
tissues,neutrophils,eosinophils,monocytes,dendritic cells,T & B
lymphocytes,hepatocytes.
Physiological actions: H₁ receptor involves in pruritis, pain,
vasodilatation, vascular permeability, hypotension,flushing
Swathi Pharma Jnan

6. Headache,tachycardia,bronchoconstriction.
In CNS,H₁ receptor activation influences cycles of sleeping &
waking,food intake,thermal regulation,emotions,aggressive
behaviour,locomotion,memory & learning.
H₂ Receptor
Location: Gastro Intestinal system, Heart
Physiological actions: They mediate gastric acid secretion,
respiratory mucus secretion.
This receptor plays an indirect role in allergy, autoimmunity,
malignant disease & graft rejection.
Swathi Pharma Jnan

7. H₃ Receptor
Location: CNS,Striatum,Substantia nigra & the cortex
Physiological actions: This receptor prevents excessive
bronchoconstriction.They mediate pruritis & involved in the
control of neurogenic inflammation.
H₄ Receptor
Location: Hematopoietic cells
Physiological actions: Allergic inflammatory response
Swathi Pharma Jnan

8.  The drugs that block the actions of histamine at H₁
receptors are called as antihistamines.
 These drugs antagonise the actions of histamine.So they
are called as H₁ antagonists.
Swathi Pharma Jnan

9. 1.Aminoalkyl ethers: Diphenhydramine HCl
Dimenhydrinate,Doxylamine succinate
Clemastine,Diphenylphyraline ,
2.Ethylene diamine derivatives: Tripelenamine HCl
3.Propylamine derivatives: Chlorpheniramine ,Triprolidine
4.Phenothiazine derivatives: Promethazine ,Trimeprazine
5.Piperazine derivatives: Chlorcyclizine,Meclizine,Buclizine
6.Miscellaneous drugs: Phenindamine,Cyproheptadine,Azatadine
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10. Second generation antihistaminics: Astemizole
Loratadine
Cetrizine
Third generation antihistaminics: Levocetrizine
Cromolyn sodium
Swathi Pharma Jnan

11. Uses:
Antihistaminic, Antiemetic
Antitussive,Antimuscarinic
Sedative,Antidyskinetic(movement disorder)
Swathi Pharma Jnan

12. Uses:
To prevent &to treat nausea,vomiting & dizziness
caused by motion sickness.
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8-Chloro theophylline
Diphenhydramine

13. Uses:
To treat seasonal rhinitis
Used as a sedative
Swathi Pharma Jnan

14. Uses:
To relieve symptoms of allergy,hay fever and common
cold.
(Symptoms include rash,watery eyes,itchy
eyes,cough,runny nose & sneezing)
Swathi Pharma Jnan

15. Uses: To treat allergic rhinitis,hay fever,skin allergy.
To treat urticaria & pruritis
Swathi Pharma Jnan

16. Uses: To treat sneezing ,runny nose,itching,watery
eyes,rashes,itching,common cold and allergy.
Swathi Pharma Jnan

17. Uses: First generation antihistaminic used to treat
urticaria,rhinitis,pruritis and other allergy symptoms.
Chlorcyclizine is anticholinergic & antiemetic
Swathi Pharma Jnan

18. Uses: To treat nausea,vomiting associated with vertigo
Used as antihistaminic
Swathi Pharma Jnan

19. Uses: To prevent nausea,vomiting and dizziness during
motion sickness.
Anti vertigo & antiemetic
Swathi Pharma Jnan

20. Uses:
To relieve red,itchy,watery eyes,sneezing,running nose
caused by allergy,hay fever and common cold.
Swathi Pharma Jnan

21. Uses: Anti histaminic
Anti allergic
Swathi Pharma Jnan

22. Uses: Antihistaminic
To treat insomnia
(Side effect of this drug is sleepiness,drowsiness)
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23. Uses: Antiallergic
To treat motion sickness
To treat nausea & Vomiting
Sedative
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HCl

24. Uses: Anti psychotic
Antihistamine
Antiemetic
Sedative
Swathi Pharma Jnan

25. Uses:Antihistaminic
Antiserotonine,Antipruritic, Antihypersensitivity
To treat allergic rhinitis,vasomotor rhinitis,allergic
conjuctivitis,Angioedema,urticaria & migraine
Swathi Pharma Jnan

26. Uses: H₁-Receptor antagonist
Anti allergic
Swathi Pharma Jnan

27. Uses:
Antihistamine
To treat allergy,urticaria & inflammation
Swathi Pharma Jnan

28. Uses: To treat anaphylaxis(serious allergic reaction)
Swathi Pharma Jnan

29. Uses:
Symptomatic relief of runnynose,sneezing,itching,hay
fever or other upper respiratory allergy.
To treat urticaria
Swathi Pharma Jnan

30. Uses: Antihistaminic
To relieve allergy,watery eyes,runny nose &
sneezing.
Swathi Pharma Jnan

31. Uses:
It prevents the release of histamine and other chemical
substances which cause inflammation
Used to treat mastocytosis(causes flushing,itchy skin
etc..,)
Swathi Pharma Jnan

32.  H₁ antagonists act by competitively inhibiting the effects of
histamine at H₁ receptor.
 These drugs show competitive antagonism of histamine
binding to cellular receptors ,which are present on various
tissues or cells.
 H₁ receptor blockade results in decreased vascular
permeability, reduction in allergic symptoms,pruritis etc..,
Swathi Pharma Jnan

33. Swathi Pharma Jnan