Blockage prevents the activation of the H1 receptors by histamine, preventing the symptoms associated with allergies from occurring. Fexofenadine does not readily cross the blood–brain barrier, so is less likely to cause drowsiness in comparison to other antihistamines that readily cross that barrier (i.e., first-generation antihistamines such as diphenhydramine). In general, fexofenadine takes about an hour to take effect, though this may be affected by the choice of dosage form and the presence of certain foods.Fexofenadine also exhibits no anticholinergic, antidopaminergic, alpha 1-adrenergic, or beta-adrenergic receptor-blocking effects. Pharmacokinetics
Absorption: After oral application, maximum plasma concentrations are reached after 2–3 hours. Fexofenadine should not be taken with a high-fat meal, as mean concentrations of fexofenadine in the bloodstream are seen to be reduced from 20 to 60% depending on form of medication (tablet, ODT, or suspension). Distribution: Fexofenadine is 60–70% bound to plasma proteins, mostly albumin. Metabolism: Fexofenadine is a substrate of CYP3A4, but only about 5% is metabolized by the liver, indicating that hepatic metabolism is relatively minor in clearance from the body. Elimination: Most of the substance is eliminated unchanged via the feces (80%) and urine (11–12%). Interactions
Taking erythromycin or ketoconazole while taking fexofenadine does increase the plasma levels of fexofenadine, but this increase does not influence the QT interval. The reason for this effect is likely due to transport-related effects, specifically involving p-glycoprotein (p-gp). Both erythromycin and ketoconazole are inhibitors of p-gp, a transporter protein involved in preventing the intestinal absorption of fexofenadine.
Fexofenadine, sold under the brand name Allegra among others, is an antihistamine pharmaceutical drug used in the treatment of allergy symptoms, such as hay fever and urticaria.Therapeutically, fexofenadine is a selective peripheral H1 blocker. It is classified as a second-generation antihistamine because it is less able to pass the blood–brain barrier and cause sedation, compared to first-generation antihistamines.It was patented in 1979 and came into medical use in 1996. It is on the World Health Organizations List of Essential Medicines. Fexofenadine has been manufactured in generic form since 2011. In 2019, it was the 283rd most commonly prescribed medication in the United States, with more than 1 million prescriptions. Medical uses
Fexofenadine is used for relief from physical symptoms associated with seasonal allergic rhinitis and for treatment of chronic urticaria. It does not cure, but rather prevents the aggravation of allergic rhinitis and chronic idiopathic urticaria, and reduces the severity of the symptoms associated with those conditions, providing relief from repeated sneezing, runny nose, itchy eyes or skin, and general body fatigue. In a 2018 review, fexofenadine, along with levocetirizine, desloratadine, and cetirizine, was cited to be a safe to use for individuals with inherited long QT syndrome. Efficacy
For the treatment of allergic rhinitis, fexofenadine is similarly effective to cetirizine, but is associated with less drowsiness than cetirizine.