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53 Cards in this Set

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  • Back
Primary use of antihistamines is management of?
ALLERGIC RHINITIS
All generations are _______ efficacious for this condition.
equally
_______ agents are used for many other clinical conditions.
1ST gen
histamine characteristics? 3
An ‘autacoid’ - a local regulatory substance
Small molecule > Bioamine
Antihistamine structure is similar to histamine
HISTAMINE RECEPTORS are connected to _________?
G proteins

G proteins are associated with various post receptor signaling mechanisms
where do we find histamine? 5
Mostly in tissues exposed to environment and subject to injury....

Lungs
Mucous membranes (nasal)
Stomach and duodenum
Skin
Basophils
Most histamine is stored in _______ and _______ in a protected package.
Mast cells

basophils
antigen - antibody combination causes a release that is an _________ respnse, requiring energy (degranulation).
exocytotic
_______________ caused by AG – AB formation takes days to replenish.
Degranulation
Various __________ and ________ effects can cause release of histamine also.
chemicals

mechanical effects
Morphine and tubocurarine stimulated release _______ require energy.
-doesn’t
_________ histamine is formed in some tissues such as stomach, epidermis, and brain.
Non-Mast cell
___________ is primarily eliminated by rapid metabolism
‘Released histamine’
Functions of histamine? 4
Role in allergy and anaphylaxis
Mediator of gastric acid secretion
Regulator of microcirculation
Serves as a neurotransmitter in CNS (histaminergic neurons)
function of histamine in skin testing?
Triple response in skin (skin testing)
what is the triple response in skin testing?
Reddening – vasodilation

Wheal - vessel leakage

Flare - axon reflex .... peripheral vasodilation
can antihistamines block the triple skin response?
yes
H1–H4 histamine receptor location
found in the brain
H1 histamine receptor location
SM, heart, endothelium
H2 histamine receptor location
SM, stomach, heart, mast cells
H3 histamine receptor location
pre-synaptic autoreceptors
H4 histamine receptor location
BM, leukocytes, lung
H1 receptor actions? (4)

(symptoms seen in allergy)
-contraction of bronchial and intestinal smooth muscle
-vasodilation
-increased capillary permeability
-Pruritis
Competitive H1 antagonists (5)
chlorpheniramine(Chlortrimeton)
diphenhydramine(Benadryl)
fexofenadine (Allegra)
loratadine (Claritin)
desloratadine (Clarinex)
H2 receptor actions (4)
-gastric acid
-vasodilation
-Inhibition of neutrophil activation
-Inhibition of T-cell cytotoxicity
H2 receptor antagosists (4)

(pizza protectors)
cimetadine(Tagamet)
ranitadine(Zantac)
famotidine(Pepcid)
nizatidine(Axid)
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
1st generation H1 receptor antagonists (6)
chlorpheniramine(Chlortrimetron)
dimenhydrinate(Dramamine)
diphenhydramine(Benadryl)
hydroxine(Atarax)
meclizine(Antivert)
promethazine(Phenergan)
2nd and 3rd generation H1 receptor antagonist (4)
cetrizine(Zyrtec)
desloratadine(Clarinex)
loratidine(Claratin)
fexofenadine(Alegra)
intranasal H1 receptor antagonist?
azelastine(Astelin)
all H1 blockers are EQUALLY EFFECTIVE in their antihistamine effect. Choice is usually based on? (4)
-duration
-side-effect profile
-risk of interactions
-cost
They prevent better than reverse symptoms.

T or F
T
general effects of 1st generation antihistamines? (6)
H1 blockade effect
CNS actions (sedative & antiemetic)
Anticholinergic activity
Local anesthetic
Antiemetic
Antitussive
drugs that have SARS similar to antihistamines? (5)
Anticholinergics
Adrenergics
Ganglionic blockers
Local anesthetics
Phenothiazines
antihistamines ADME (3)
-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.
other antihistamine ADME....
-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
Clinical Uses of H1 Blockers (9)
-Pollenosis
-Urticaria
-Allergic Rhinitis
-Vasomotor rhinitis
-Serum sickness(epi)
-Drug induced angioedema
-Blood transfusion reactions
-G.I. Allergies
-Bronchial asthma
-Systemic anaphylaxis
Do H1 blockers relieve nasal congestion?
Don’t relieve nasal congestion so may be combined with alpha agonist (pseudoephedrine)
Other clinical uses of H1 blockers that are mostly dependent on anticholinergic effects? [3]
common cold
motion sickness
parkinsons dz
Other clinical uses of H1 blockers? [3]
-Emesis/ motion sickness(promethazine]
-Sedation/Hypnosis
-Local Anesthetic
2nd generation antihistamines effects compared to 1st gen's(2)
DECONGESTANT ACTIVITY (equal to that of pseudoephedrine)

ANTIINFLAMMATORY EFFECTS (useful in asthma?)
best 2nd generation AH?
Desloratadine (Clarinex)
Diphenhydramine effective for [6]

(poster child)
treating histamine mediated effects like allergic rhinitis
Colds (rhinitis and cough) motion sickness
Parkinson
Pruritis
insomnia
Clinical Problems - mostly with 1st generation?
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
Clinical Problems (3)
G.I.
Anorexia
Atropine-like effects (anti-muscarinic)
Allergies
Low incidence (mostly contact dermatitis topical use of 1st generation)
Acute Poisoning with Classical Antihistamines (wide margin of safety)
Acute poisoning looks like atropine poisoning. CNS effects are more serious.
Treatment
Supportive
For convulsions (diazepam)
For anticholinergic effects (physostigmine)
Acute overdose with 2nd & 3rd generation:
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
Non - antihistamines used to manage seasonal (allergic) rhinitis
Cromolyn
-Alpha agonists - -pseudoephedrine to dry secretions
-Intranasal corticosteroids (INC)
Cromolyn (4)
Nasal spray and ophthalmic prep (allergic conjunctivitis)
Prophylactic use
Inhibits mast cell release of histamine
Also used to manage asthma
Intranasal corticosteroids (INC) (5)
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
Antihistamines
1st generation (3)
Less selective
More secondary effects (sedation and anticholinergic)
More clinical uses
Antihistamines
2nd and 3rd generation (3)
More selective (non-sedating)
Fewer secondary effects ..... narrower spectrum of uses
Are all antihistamines equally effective in treating allergic rhinitis?
yes