Histamine pharmacology
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Transcript of Histamine pharmacology
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Histamine
Histidine
Histamine
histidine decarboxylase
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Non–mast cell sites epidermis, gastric mucosa, neurons within the CNS
granules of MAST cells
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mediator of allergy, inflammation, gastric acid secretion
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Histamine receptors GPCRs
H1 receptor
-IP3 ,DAG ↑
-bronchoconstriction-Vasodilation via NO
-Brain , Ganglia
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H2 receptor
↑cAMP
Acid secretion
Vasodilation
Brain , Heart
H3 – cAMP↓presynaptic in Brain - ↓histamine release H4
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Histamine
Blood vessels
H1 – vasodilation -via release of NO from endothelium–short lasting
H2 –vascular smooth muscles -vasodilation –sustained
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Intradermal histamine –triple response of Lewis
Red spot , Wheal , Flare
Increase capillary permeability
Itching
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Histamine
H1 - smooth muscle contraction Bronchoconstriction
CNS – histamine as neurotransmitter H1 - ↓appetite , ↑wakefulness
H2 - gastric gland –acid secretion
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Histamine -Role in Allergic responses
Immediate hypersensitivity reaction - IgE
Mast cell
Antigen
IgE
Histamine release
Urticaria
Angioedema
Anaphylactic shock
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UrticariaAngioedema
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Histamine
Synthesis
Storage
Receptors – H1 ,2 ,3 ,4
Blood vessels , Triple responseAcid secretion
Allergic responses
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H1 receptor antagonists
1st generation
-sedation
- antichollinergic property
2nd generation
-absence of sedation
-devoid of antichollinergic effects
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1st generation H1 antagonists
Highly sedative Promethazine , Dimenhydrinate
Moderately sedative
Pheniramine , Meclizine Mild sedative Chlorpheniramine , Clemastine
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H1 receptor antagonists
ACTIONS
Antagonism of Histamine effects Like bronchoconstriction , triple response , itching → blocked
Antiallergic action
Control of urticaria , itching , angioedema
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H1 receptor antagonists
ACTIONS
Anticholinergic effects High – Promethazine , Dimenhydrinate , Pheniramine
CNS depression – 1st generation
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H1 receptor antagonists
Adverse effects
Sedation ,↓alertness Motor incoordination Tendency to fall sleep
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Anticholinergic Blurred vision Constipation Dry mouth Urinary retention ABCD & U
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H1 receptor antagonists
2nd generationMinimal sedation
No anticholinergic effects
Additional antiallergic mechanisms
FexofenadineLoratidine
Cetrizine
EbastineRupatidine
Use Allergic rhinitis & conjunctivitis , Urticaria
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H1 receptor antagonists
USES Allergic disordersUrticaria , Angioedema , Conjunctivitis , Rhinitis
supportive in anaphylactic shock
Itching (Pruritus)Chlorpheniramine Diphenhydramine
Common Cold
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H1 receptor antagonists
USES
Motion sickness Promethazine , Diphenhydramine , Meclizine
Morning sickness (vomiting of early pregnancy)
Doxylamine , Meclizine
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Vertigo Cinnarizine – H1 antihistaminic , anticholinergic ,anti 5-HT vasodilator
Dimenhydrinate , Promethazine
H1 receptor antagonists
USES
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Parkinsonism Promethazine - anticholinergic effect
H1 receptor antagonists
USES
Cough suppressionChlorpheniramine , Diphenhydramine
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Let’s reviseH1 receptor antagonists
1st , 2nd generations
Difference
Adverse effects -sedation
Uses - many
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Today's question
Terfinadine , Astemizole –Antihistaminics
Banned – WHY ???
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