Seconds generations
agents
1.
Piperidines
a.
Loratadine [Claritin]
b.
Desloratadine [clarinex]
i.
poor cns penetration : reduces sedation
ii.
ittle or no anticholinergic activity
c.
desloratadine
i.
is the active metabolite loratadine
ii.
Has about 15-fold greater affinity for the H1
receptor than the parent compound
d.
Fexophenadine
2.
Clesmatine
a.
Is a second-generation ethanolamine
b.
Longer duration of action than dimenhydramine
c.
It has some antiemetic activity
3.
Alkyamines
a.
Acriastine
i.
Acriastine is not associated cardiac effects
b.
Cetirizine [zyrtec]
i.
Cetirizine is not associated with cardiac
abnormalities
ii.
Cetirizine has poor penetration into cns
iii.
Cetirizine is less sedating
iv.
It is ineffective
for motion sickness or antiemesis
Pharmacologic properties of histamine (H1)-receptors
antagonist
-well absorbed after oral administration
1st
generation 2nd
generation
Onset 30 min
Duration
3-8 hours 3-24
hours
-
H1-receptors antagonist are lipid soluble; most
first-generation agents cross the blood-brain barrier
-
H1-receptors antagonist are metabolized in the
liver
Pharmacologic actions
-
Many H1-receptor antagonist, especially the
ethanolaminenes, phenothiazines, and ethylendiamines, have
muscarinic-chholinergic antagonist activities
H1-receptor
Therapeutic uses
1.
Treatment of alergioc rhinitis and
conjunctivitis
a.
Clesmatine is approved for the treatment of
rhinorhea
b.
Many antihistamines are used to treat the common
cold, based on their anticholinesgic properties, but they are only marginally
effective for this use
c.
Diphenhydramine also has an atitusive effect not
mediated by H1-receptors antagonism
2.
Treatment of uticaria and atopic dermatitis
3.
Sedatives, several (doxylamine, diphenhydramine)
are marked as over-the-counter)
4.
Prevention of motion sickness
5.
Appetite suppressant
Adverse effects
Significantly reduced with second-generation agents
1.
Sedations, dizziness, and loss of appetite
2.
These agets can cause gastrointestinal upset,
nausea, and constipation or diarrhea.
3.
H1-receptors antagonist produce anticholinergic
effects (dry mouth, blurred vision, and urine retention)
Two second-generation H1 antagonist, astemizole and
terfetadine (a prodrug of fexofenadine) were discontinued or removed from the
market because they were associated with q-t prolongation and ventricular tachy
cardiac
Histamine (H2)-receptors
antagonist
-
Cimetidine [tagamet]
-
Ranitidine [zantac]
-
Famotidine [pepcid ac]
-
Nizatidine [axid]
Competitive antagonist at the H2-receptors, which
predominates in the gastric parietal cell
Used in treatment of
1.
Gastrointestinal
disorders, including heartburn and acid-induced indigestion
2.
These agents promote the healing of gastric and duodenal ulcers
3.
Used to treat hypersecretory states suchs as zollinger-ellison syndrome
Pharmacokinetics
-
The bioavailability of h2- antagonis goes from
50% for ranitidine and famotidine to approximately 90% for nizatidine and
advised dosages take this into account
-
They taken especially in the evening to reduce
night gastric acidity
-
Their elimination is primarily renal
-
Cimetidine inhibits cytochrome p-450 and
increases the concentrations and the effects of many other drugs
Adverse effects
-
H2-antagonist are generally well-tolerated,
except for cimetidine where all of the following adverse drug reactions (ADRs)
are common
-
Infrequent ADRs include hypotension
-
Rare ADRs include : headache, tiredness, dizziness, confusion, diarrhea, constipation, and
rash
-
Additionally, cimetidine may also cause
gynecomastia in male, loss of libido, and impotence, which are reversible upon
discontinuation
The chrmones
-
Cromolyn [intal]
-
Nedocromil sodium
These are administered by inhalation
They inhibit the releaseof histamine and other autocoids
from the mast cell
Each is used prophylatically in the treatment of asthma
They do not reverse bronchospasm
Adverse effects
confind to the site of application
-
sore troath
-
dry mouth
author : health-informa.com
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