Description

Fexofenadine hydrochloride is a second-generation antihistamine used to relieve allergy symptoms. It’s the active metabolite of terfenadine but, unlike its predecessor, it doesn’t cause cardiotoxic side effects. Fexofenadine is a non-sedating antihistamine because it does not cross the blood-brain barrier. It is available as oral tablets and suspensions.

Indication

Fexofenadine is primarily indicated for the treatment of symptoms associated with:

• Seasonal Allergic Rhinitis: It effectively relieves symptoms like sneezing, runny nose, itchy or watery eyes, and itching of the nose or throat caused by hay fever and other seasonal allergies.
• Chronic Idiopathic Urticaria: It is also used to treat and relieve the itching and hives (urticaria) associated with this skin condition.

Mechanism of Action

Fexofenadine’s mechanism of action involves selectively blocking the effects of histamine, a chemical released by the body during an allergic reaction. The process is as follows:

1. Histamine Release: When an allergen enters the body, the immune system releases histamine from mast cells. Histamine then binds to and activates H1 receptors on cells throughout the body, triggering the characteristic symptoms of an allergic reaction.
2. H1 Receptor Antagonism: Fexofenadine acts as a potent and selective peripheral H1 receptor antagonist. This means it binds to the H1 receptors on the surface of cells, effectively blocking histamine from binding to them.
3. Symptom Relief: By preventing histamine from activating H1 receptors, fexofenadine prevents the cascade of events that cause allergy symptoms like vasodilation, increased vascular permeability (leading to swelling and a runny nose), and itching. This action provides relief without causing significant drowsiness, as it does not affect histamine receptors in the central nervous system.