Fexofenadine, commonly known by the brand name Allegra, is an antihistamine medication used to relieve allergy symptoms. Its mechanism of action involves the following:
1. **Histamine Blockade:** Fexofenadine is an H1 receptor antagonist. Histamine is a chemical released by the body during allergic reactions, leading to symptoms like sneezing, runny nose, itching, and watery eyes. Fexofenadine works by binding to and blocking H1 receptors in various tissues, including the nasal mucosa and blood vessels.
2. **Anticholinergic Activity:** Fexofenadine has limited anticholinergic effects, which means it has a reduced tendency to cause drowsiness compared to some other older-generation antihistamines. This property makes it more suitable for daytime use and situations where alertness is important.
3. **Selectivity:** Fexofenadine is considered a selective H1 antagonist, primarily targeting histamine receptors in the periphery (such as those in the nasal passages and skin) rather than crossing the blood-brain barrier to affect central nervous system receptors. This selective action contributes to its reduced sedative effects.
By blocking H1 receptors and reducing the effects of histamine, fexofenadine helps alleviate allergy symptoms such as sneezing, itching, runny nose, and hives, without causing significant drowsiness in most people. It is commonly used to manage seasonal allergies (hay fever) and chronic idiopathic urticaria (hives of unknown cause).