Description

Levocetirizine dihydrochloride is a third-generation, non-sedating antihistamine. It is the active (levo) enantiomer of cetirizine. By isolating the active enantiomer, levocetirizine is able to provide its therapeutic effect at half the dose of cetirizine, with a similar or even improved safety profile. It is a potent and highly selective antagonist of peripheral H1 receptors and is available in oral formulations like tablets and oral solution.

Indication

Levocetirizine is indicated for the symptomatic treatment of various allergic conditions in adults and children:

• Seasonal Allergic Rhinitis (Hay Fever): It is used to relieve symptoms such as sneezing, runny nose, nasal itching, and itchy, watery eyes.

• Perennial Allergic Rhinitis: It is effective for managing the symptoms of year-round allergies.
• 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

The mechanism of action of levocetirizine is based on its potent and selective inhibition of histamine’s effects. The process is as follows:

1. Histamine Release: During an allergic reaction, allergens trigger the release of histamine from mast cells. This histamine then binds to and activates H1 receptors on cells throughout the body, causing the characteristic allergic symptoms.

2. H1 Receptor Antagonism: Levocetirizine acts as a highly selective and potent peripheral H1 receptor antagonist. It binds to the H1 receptors, effectively blocking histamine from activating them. This action prevents the downstream effects of histamine, such as vasodilation, increased vascular permeability (leading to a runny nose and swelling), and itching.
3. Potency and Selectivity: Levocetirizine’s high potency allows it to provide effective symptom relief at a lower dose. Its selectivity for peripheral H1 receptors, combined with its inability to readily cross the blood-brain barrier, means it provides allergy relief with a very low risk of central nervous system side effects like sedation.
4. Anti-inflammatory Effects (Secondary): In addition to its antihistamine properties, levocetirizine has been shown to have anti-inflammatory effects. It can inhibit the migration of eosinophils and the release of other pro-inflammatory mediators, which further contributes to its effectiveness in managing allergic rhinitis and urticaria.