Cetirizine hydrochloride is an oral antihistamine used to relieve symptoms of allergic rhinitis caused by allergens like dust mites and animal dander. It selectively inhibits H1 receptors, resulting in fewer sedative effects compared to first-generation antihistamines, with common side effects including somnolence and dizziness. Cetirizine is effective in managing allergies by reducing inflammation and stabilizing mast cells, thus providing relief from allergic reactions.

1. Cetirizine
Cetirizine hydrochloride is an orally active and
selective H1-receptor antagonist.
Cetirizine hydrochloride is a racemic
compound with an empirical formula of
C21H25ClN2O3•2HCl. The molecular weight is
461.82 g/mol.
The allergic individual create a special type of antibody
call Immunoglobin E(Ige), when comes contact with the
environmental substances such as histamine, which
produce allergic symptoms in skin, nose, eyes, chest,
etc.

2. Allergy
• Allergies are
hypersensitive
responses from the
immune system to
substances that either
enter or come into
contact with the body.
• Allergies are a very
common overreaction
of the immune system
to usually harmless
substances.
Allergen
• An allergen is a usually
harmless substance
capable of triggering a
response that starts in the
immune system and
results in an allergic
reaction.
• common allergens include
• pollens
• dust mites
• animal dander
• mold
• medication
• insect venom
• food.
Symptoms
• Dust and pollen
• blocked nose
• itchy eyes and nose
• runny nose
• swollen and watery eyes
• Cough
• Skin reactions
• flaking
• itching
• Rashes
• Food
• vomiting
• swollen tongue
• swelling of the lips face,
and throat
• stomach cramps
• itchiness in the mouth

3. Generic name: Cetirizine hydrochloride.
Chemical name: [2- [4- [(4-chlorophenyl) phenylmethyl] -1- piperazinyl] ethoxy]acetic acid,
dihydrochloride.
• Cetirizine, a metabolite of hydroxyzine, is an
antihistamine drug. Its main effects are
achieved through selective inhibition of
peripheral H1 receptors.
• Cetirizine was rapidly absorbed with a time to
maximum concentration of about 1 hour after
oral administration of tablets or syrup
formulation in adult volunteers.
• Cetirizine hydrochloride syrup is indicated for
the relief of symptoms associated with
perennial allergic rhinitis due to allergens such
as dust mites, animal dander and molds.
Cetirizine is a second generation drug.
Second generation antihistamines are developed to avoid or
reduce the sedative effects of drug.
Second-generation antihistamines cross the blood–brain barrier
to a much lower degree than the first-generation antihistamines.
Their main benefit is they primarily affect peripheral histamine
receptors and therefore are less sedating.
Cetirizine hydrochloride

4. Mode of action of Allergen
• Mast cells generate mediators of
inflammation which are stored in
granules and secreted on activation
either by allergen crosslinking of
membrane-bound IgE or through other
stimuli.
• The H1 receptor is a
histamine receptor belonging to the
family of rhodopsin-like G-protein-
coupled receptors. This H1 receptor is
activated by the biogenic amine
histamine. It is expressed in smooth
muscles, on vascular endothelial cells,
in the heart, and in the central nervous
system.

5. Mode of action of Cetirizine

6. H1-antihistamines interfere with the agonist action of histamine at the H1
receptor and are administered to attenuate inflammatory process in order to
treat conditions such as allergic rhinitis, allergic conjunctivitis, and urticaria.
Reducing the activity of the NF-κB immune response transcription factor
through the phospholipase C and the phosphatidylinositol (PIP2) signaling
pathways.
Decreases antigen presentation and the expression of pro-inflammatory
cytokines, cell adhesion molecules, and chemotactic factors.
Lowering calcium ion concentration leads to increased mast cell stability which
reduces further histamine release.
Second-generation antihistamines are more selective for H1-receptors of the
peripheral nervous system (PNS) and do not cross the blood-brain barrier.
Consequently, these newer drugs elicit fewer adverse drug reactions.
Mode of action of cetirizine

7. Side effects of cetirizine
• The most commonly reported side effects include
somnolence, dizziness, and headache.
• Applies to cetirizine : oral solution, oral tablets and chewable tablets
Side effects include:
Adults and children ≥12 years of age: Somnolence, fatigue, dry mouth.
Insomnia reported with cetirizine hydrochloride-
pseudoephedrine hydrochloride fixed combination.
Children 2–11 years of age: Headache, pharyngitis, abdominal pain.
Children 6 months to 2 years of age: Irritability, fussiness, insomnia,
fatigue, malaise.
Cetirizine is a second generation drug. It
can cross blood brain barrier (BBB) and
result in side effects like sleepiness or
dizziness. But it is effective than first
generation drugs.
Now, third generation is most efficient
because it can not cross BBB. i.e.,
Desloratadine.
 Sheffer, A. L., & Samuels, L. L. (1990). Cetirizine: antiallergic therapy beyond traditional H1
antihistamines. Journal of Allergy and Clinical Immunology, 86(6), 1040-1046.
 Bhatia, N. M., Ganbavale, S. K., Bhatia, M. S., More, H. N., & Kokil, S. U. (2008). RP-HPLC and
spectrophotometric estimation of ambroxol hydrochloride and cetirizine hydrochloride in combined dosage
form. Indian journal of pharmaceutical sciences, 70(5), 603.
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