Histamines

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Author:
thedewhub
ID:
300193
Filename:
Histamines
Updated:
2015-04-19 19:47:36
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Histamines
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Histamines
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Histamines
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  1. Histamine is metabolized by 2 pw
    • oxidation- diamine oxidase
    • methylation- s adenosyl l methione - becomes methlylinidazole acetic acid which is the mahor urinary metabolite of histamine in man
  2. pharmacology of histamine
    • if i inject you or another subject it has ... an effect- effect of an exogenous substance
    • unilateral headache- cerebral vasodilation
  3. pathological role of histamine
    • causing HA in pt
    • gastric secretion and pain- not necessarily a physiologic mediator, many factors affect acid secretion
  4. triple response- 3 comps h1 and h2
    • direct dilation of terminal arterioles
    • stimulation of a local axon reflex- flare of local afferent nerves with discahrge of vasodilating efferent nerves
    • wheal- edema increased perm of venules seperating the endothelial cells
  5. H1 effect
    • intense vasodilation of resistance vessels- hypotension
    • contraction of bronchiolar smooth muscle
  6. h1 induced relaxtion of vascular smooth muscle requires
    intact endothelial cell which release EDRF aka NO
  7. H2
    • in the gastric mucousa- stimulation increase pepsin and acid output- promoting secretion
    • also in atria- activates HR chronotropic
  8. why does an h2 blocker have more gastric than cardiac effect?
    more histamine in stomach than blood- not blocking any effect in heart
  9. h1 pw
    phospholoipase c- ca is key
  10. h2- pw
    increase in cAMp
  11. immunologics and histamine
    have histamine release in allergic rxn- 1 immunologic specific- because of sensitized ab binds to
  12. antigen induces histamine release
    • step 1 make ige becuase of sensitization
    • step 2 IgE binds to mast cells
    • step 3 pollen crosslink to tissue bound ige and mast cell activates to release histamine
  13. nonimmunologcial rxn
    histamine releasing drugs- not an immunologic response- like neuromusclar drugs or codeine, contrast media,
  14. clinical problems of histamine
    • urticaria, pigmentosa, systemic mastocytosis
    • need to be treated like with antagonists
    • anaphylaxis- epinephrine
    • inflmmation
  15. antihistamines
    h1 or h2 blocker
  16. h1 antagonists
    • 1st gen- sedating
    • 2nd- nonsedating
  17. 1st geb h1 blocker
    • diphenhydramine
    • tripelenamine
    • chlorphenirameine
  18. h1 therrapeutic use-
    for rhinitis, urticaria, can sedate, topical anesthetic for sore throat, for menieres,
  19. SE of h1 gen 1 blockers
    cns depressors, NV
  20. second gen h1 blockers
    • not brain penetrating- minimal cns se
    • lack anticholinergic and serotonin and much longer duraton of action
  21. h2 blockers
    • cimetidine
    • ranitidine
    • famtidine
    • nizatidine
  22. h2 therapy
    • control of gi bleeding
    • etc
    • stress related erosice sysndrome
    • trauma, burns, ARF, shock, sepsis, stroke- use h2 blocker to prevent this empirically
  23. h2 SE
    minor
  24. cimitadine
    • p450 blocker- only h2 to do this
    • theophylline- inhibition of metabolism
    • warforin- increased anticoag effect
  25. antirelease agents
    • cromoglycate prototype and nedocromyl
    • aniallergic drugs
    • cromolyn prevents antigen induced mast cell degranulation in young with allergic asthma
    • given prophylactically for asthma

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