Histamine pharmacology

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  • Red spot a localized red spot extending for a few millimeters around the site of injection that appears within a few seconds and reaches a maximum in 1 minute

    a wheal that is discernible in 1-2 minutes and occupies the same area as the original small red spot at the injection site.-exudation of fluid from capillaries

    a brighter red "flare," extending 1 cm beyond the original red spot and developing more slowly
  • H1, H2, and H3 receptors are distributed widely but non-uniformly in the CNS
  • Urticaria, are an outbreak of swollen, pale red bumps, patches on the skin that appear suddenly –

    Angioedema-is the rapid swelling (edema) of the dermis, subcutaneous tissue,[1] mucosa and submucosal tissues.
  • Histamine pharmacology

    1. 1. Histamine Histidine Histamine histidine decarboxylase
    2. 2. Non–mast cell sites epidermis, gastric mucosa, neurons within the CNS granules of MAST cells
    3. 3. mediator of allergy, inflammation, gastric acid secretion
    4. 4. Histamine receptors GPCRs H1 receptor -IP3 ,DAG ↑ -bronchoconstriction -Vasodilation via NO -Brain , Ganglia
    5. 5. H2 receptor ↑cAMP Acid secretion Vasodilation Brain , Heart H3 – cAMP↓ presynaptic in Brain - ↓histamine release H4
    6. 6. Histamine Blood vessels H1 – vasodilation -via release of NO from endothelium–short lasting H2 –vascular smooth muscles -vasodilation –sustained
    7. 7. Intradermal histamine –triple response of Lewis Red spot , Wheal , Flare Increase capillary permeability Itching
    8. 8. Histamine H1 - smooth muscle contraction Bronchoconstriction CNS – histamine as neurotransmitter H1 - ↓appetite , ↑wakefulness H2 - gastric gland –acid secretion
    9. 9. Histamine -Role in Allergic responses Immediate hypersensitivity reaction - IgE Mast cell Antigen IgE Histamine release Urticaria Angioedema Anaphylactic shock
    10. 10. UrticariaAngioedema
    11. 11. Histamine Synthesis Storage Receptors – H1 ,2 ,3 ,4 Blood vessels , Triple response Acid secretion Allergic responses
    12. 12. H1 receptor antagonists 1st generation -sedation - antichollinergic property 2nd generation -absence of sedation -devoid of antichollinergic effects
    13. 13. 1st generation H1 antagonists Highly sedative Promethazine , Dimenhydrinate Moderately sedative Pheniramine , Meclizine Mild sedative Chlorpheniramine , Clemastine
    14. 14. H1 receptor antagonists ACTIONS Antagonism of Histamine effects Like bronchoconstriction , triple response , itching → blocked Antiallergic action Control of urticaria , itching , angioedema
    15. 15. H1 receptor antagonists ACTIONS Anticholinergic effects High – Promethazine , Dimenhydrinate , Pheniramine CNS depression – 1st generation
    16. 16. H1 receptor antagonists Adverse effects Sedation ,↓alertness Motor incoordination Tendency to fall sleep
    17. 17. Anticholinergic Blurred vision Constipation Dry mouth Urinary retention ABCD & U
    18. 18. H1 receptor antagonists 2nd generation Minimal sedation No anticholinergic effects Additional antiallergic mechanisms Fexofenadine Loratidine Cetrizine Ebastine Rupatidine Use Allergic rhinitis & conjunctivitis , Urticaria
    19. 19. H1 receptor antagonists USES Allergic disorders Urticaria , Angioedema , Conjunctivitis , Rhinitis supportive in anaphylactic shock Itching (Pruritus) Chlorpheniramine Diphenhydramine Common Cold
    20. 20. H1 receptor antagonists USES Motion sickness Promethazine , Diphenhydramine , Meclizine Morning sickness (vomiting of early pregnancy) Doxylamine , Meclizine
    21. 21. Vertigo Cinnarizine– H1 antihistaminic , anticholinergic ,anti 5-HT vasodilator Dimenhydrinate , Promethazine H1 receptor antagonists USES
    22. 22. Parkinsonism Promethazine - anticholinergic effect H1 receptor antagonists USES Cough suppression Chlorpheniramine , Diphenhydramine
    23. 23. Let’s revise H1 receptor antagonists 1st , 2nd generations Difference Adverse effects -sedation Uses - many
    24. 24. Today's question Terfinadine , Astemizole –Antihistaminics Banned – WHY ???

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