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53 Cards in this Set
- Front
- Back
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Primary use of antihistamines is management of?
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ALLERGIC RHINITIS
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All generations are _______ efficacious for this condition.
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equally
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_______ agents are used for many other clinical conditions.
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1ST gen
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histamine characteristics? 3
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An ‘autacoid’ - a local regulatory substance
Small molecule > Bioamine Antihistamine structure is similar to histamine |
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HISTAMINE RECEPTORS are connected to _________?
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G proteins
G proteins are associated with various post receptor signaling mechanisms |
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where do we find histamine? 5
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Mostly in tissues exposed to environment and subject to injury....
Lungs Mucous membranes (nasal) Stomach and duodenum Skin Basophils |
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Most histamine is stored in _______ and _______ in a protected package.
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Mast cells
basophils |
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antigen - antibody combination causes a release that is an _________ respnse, requiring energy (degranulation).
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exocytotic
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_______________ caused by AG – AB formation takes days to replenish.
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Degranulation
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Various __________ and ________ effects can cause release of histamine also.
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chemicals
mechanical effects |
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Morphine and tubocurarine stimulated release _______ require energy.
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-doesn’t
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_________ histamine is formed in some tissues such as stomach, epidermis, and brain.
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Non-Mast cell
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___________ is primarily eliminated by rapid metabolism
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‘Released histamine’
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Functions of histamine? 4
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Role in allergy and anaphylaxis
Mediator of gastric acid secretion Regulator of microcirculation Serves as a neurotransmitter in CNS (histaminergic neurons) |
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function of histamine in skin testing?
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Triple response in skin (skin testing)
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what is the triple response in skin testing?
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Reddening – vasodilation
Wheal - vessel leakage Flare - axon reflex .... peripheral vasodilation |
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can antihistamines block the triple skin response?
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yes
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H1–H4 histamine receptor location
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found in the brain
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H1 histamine receptor location
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SM, heart, endothelium
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H2 histamine receptor location
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SM, stomach, heart, mast cells
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H3 histamine receptor location
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pre-synaptic autoreceptors
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H4 histamine receptor location
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BM, leukocytes, lung
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H1 receptor actions? (4)
(symptoms seen in allergy) |
-contraction of bronchial and intestinal smooth muscle
-vasodilation -increased capillary permeability -Pruritis |
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Competitive H1 antagonists (5)
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chlorpheniramine(Chlortrimeton)
diphenhydramine(Benadryl) fexofenadine (Allegra) loratadine (Claritin) desloratadine (Clarinex) |
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H2 receptor actions (4)
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-gastric acid
-vasodilation -Inhibition of neutrophil activation -Inhibition of T-cell cytotoxicity |
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H2 receptor antagosists (4)
(pizza protectors) |
cimetadine(Tagamet)
ranitadine(Zantac) famotidine(Pepcid) nizatidine(Axid) |
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Generation classification based on CNS impairment
BAC equivalent? |
1st-most 7.67-27.5 BAC .05-.1
2nd- .21-.29 BAC 0.0-.05 3rd-least 0.0 BAC 0.0 |
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1st generation H1 receptor antagonists (6)
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chlorpheniramine(Chlortrimetron)
dimenhydrinate(Dramamine) diphenhydramine(Benadryl) hydroxine(Atarax) meclizine(Antivert) promethazine(Phenergan) |
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2nd and 3rd generation H1 receptor antagonist (4)
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cetrizine(Zyrtec)
desloratadine(Clarinex) loratidine(Claratin) fexofenadine(Alegra) |
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intranasal H1 receptor antagonist?
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azelastine(Astelin)
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all H1 blockers are EQUALLY EFFECTIVE in their antihistamine effect. Choice is usually based on? (4)
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-duration
-side-effect profile -risk of interactions -cost |
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They prevent better than reverse symptoms.
T or F |
T
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general effects of 1st generation antihistamines? (6)
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H1 blockade effect
CNS actions (sedative & antiemetic) Anticholinergic activity Local anesthetic Antiemetic Antitussive |
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drugs that have SARS similar to antihistamines? (5)
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Anticholinergics
Adrenergics Ganglionic blockers Local anesthetics Phenothiazines |
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antihistamines ADME (3)
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-All gens have good oral absorption
-1st gens may be used other routes -Both well distributed .. but 2nd and 3rd don’t cross BBB readily (little or no sedation) -All generations metabolized in liver. |
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other antihistamine ADME....
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-1st gen duration of action 4-6 hrs
-2nd & 3rd gen duration of action 12-24 hrs -1st gen ..... interactions with CNS depressants and anticholinergics -2nd and 3rd generation ..... no important clinical interactions |
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Clinical Uses of H1 Blockers (9)
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-Pollenosis
-Urticaria -Allergic Rhinitis -Vasomotor rhinitis -Serum sickness(epi) -Drug induced angioedema -Blood transfusion reactions -G.I. Allergies -Bronchial asthma -Systemic anaphylaxis |
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Do H1 blockers relieve nasal congestion?
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Don’t relieve nasal congestion so may be combined with alpha agonist (pseudoephedrine)
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Other clinical uses of H1 blockers that are mostly dependent on anticholinergic effects? [3]
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common cold
motion sickness parkinsons dz |
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Other clinical uses of H1 blockers? [3]
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-Emesis/ motion sickness(promethazine]
-Sedation/Hypnosis -Local Anesthetic |
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2nd generation antihistamines effects compared to 1st gen's(2)
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DECONGESTANT ACTIVITY (equal to that of pseudoephedrine)
ANTIINFLAMMATORY EFFECTS (useful in asthma?) |
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best 2nd generation AH?
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Desloratadine (Clarinex)
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Diphenhydramine effective for [6]
(poster child) |
treating histamine mediated effects like allergic rhinitis
Colds (rhinitis and cough) motion sickness Parkinson Pruritis insomnia |
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Clinical Problems - mostly with 1st generation?
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SEDATION is most common in adults
Avoid use of alcohol with classical H1 Blockers 1st generation is variable from agent to agent 2nd generation has low incidence of sedative problems 3rd generation none apparent |
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Clinical Problems (3)
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G.I.
Anorexia Atropine-like effects (anti-muscarinic) Allergies Low incidence (mostly contact dermatitis topical use of 1st generation) |
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Acute Poisoning with Classical Antihistamines (wide margin of safety)
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Acute poisoning looks like atropine poisoning. CNS effects are more serious.
Treatment Supportive For convulsions (diazepam) For anticholinergic effects (physostigmine) |
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Acute overdose with 2nd & 3rd generation:
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less of a problem .... they don’t enter CNS readily.
Greater risk of problems with cardiac arrhythmias Tend to prolong QT interval do not seem to intensify CNS effects of other drugs or alcohol |
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Non - antihistamines used to manage seasonal (allergic) rhinitis
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Cromolyn
-Alpha agonists - -pseudoephedrine to dry secretions -Intranasal corticosteroids (INC) |
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Cromolyn (4)
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Nasal spray and ophthalmic prep (allergic conjunctivitis)
Prophylactic use Inhibits mast cell release of histamine Also used to manage asthma |
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Intranasal corticosteroids (INC) (5)
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Some recommend to initiate therapy with INC
Effective ... but expensive Improves itching, rhinorrhea, congestion Not much help for allergic conjunctivitis Works best if start before allergy season begins! Also quite useful in management of asthma |
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Antihistamines
1st generation (3) |
Less selective
More secondary effects (sedation and anticholinergic) More clinical uses |
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Antihistamines
2nd and 3rd generation (3) |
More selective (non-sedating)
Fewer secondary effects ..... narrower spectrum of uses |
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Are all antihistamines equally effective in treating allergic rhinitis?
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yes
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