Description

Cetirizine hydrochloride is a second-generation, non-sedating antihistamine. It is a potent and selective antagonist of peripheral H1 receptors and is a major metabolite of hydroxyzine, a first-generation antihistamine. Cetirizine is well-known for its rapid onset of action and its effectiveness in relieving various allergy symptoms without causing significant drowsiness. It is available in different oral formulations, including tablets, chewable tablets, and syrup.

Indication

Cetirizine is indicated for the relief of symptoms associated with:

• Seasonal Allergic Rhinitis (Hay Fever): It is effective in treating symptoms like sneezing, runny nose, nasal itching, and watery or itchy eyes caused by pollen and other seasonal allergens.

• Perennial Allergic Rhinitis: It is also used to manage the symptoms of year-round allergies caused by allergens such as dust mites, animal dander, and mold.

• Chronic Idiopathic Urticaria (Hives): It is used to relieve the itching and reduce the size and number of hives associated with this skin condition.

Mechanism of Action

Cetirizine’s mechanism of action is primarily based on its ability to block the effects of histamine, a key chemical mediator of allergic reactions. The process is as follows:

1. Histamine Release: During an allergic response, the immune system releases histamine from mast cells. Histamine then binds to and activates H1 receptors on cells throughout the body, leading to the characteristic symptoms of an allergy.

2. H1 Receptor Antagonism: Cetirizine is a highly potent and selective peripheral H1 receptor antagonist. This means it binds to the H1 receptors on the surface of cells in the skin, eyes, nose, and other tissues, effectively blocking histamine from binding to them.

3. Symptom Relief: By preventing histamine from activating H1 receptors, cetirizine prevents the downstream effects, such as vasodilation (causing redness and swelling), increased vascular permeability (leading to a runny nose), and itching. This action provides rapid and effective relief from allergic symptoms.
4. Anti-inflammatory Effects (Secondary): In addition to its antihistaminic effects, cetirizine has been shown to have anti-inflammatory properties. It can inhibit the migration of inflammatory cells, such as eosinophils, to sites of allergic inflammation, further contributing to its overall therapeutic effect.

As a second-generation antihistamine, cetirizine does not readily cross the blood-brain barrier, which is why it provides effective relief from allergies with a much lower risk of causing sedation compared to first-generation antihistamines.