Detailed dosage guidelines and administration information for Allegra (fexofenadine hydrochloride). Includes dose adjustments, warnings and precautions. Fexofenadine (Allegra) is an antihistamine that treats and prevents allergy symptoms. It blocks histamine to reduce your symptoms. Allegra (fexofenadine) is an antihistamine used to treat allergy symptoms, including sneezing, itching, watery eyes, and a runny nose. Includes Allegra side effects, interactions, and indications. The main active ingredient in all Allegra products for allergy symptoms is an antihistamine called fexofenadine. Fexofenadine works to block a substance in your body called histamine. Allegra 120mg Tablet is used in the treatment of Urticaria, Allergic rhinitis. Find Allegra 120mg Tablet uses, composition, side-effects, price, substitutes, drug interactions, precautions, warnings, and expert advice. Allegra® provides effective relief from allergy symptoms with 0% brain interference, keeping you alert and non-drowsy. Allegra® allergy medicine family of products relieves symptoms of indoor, outdoor, and seasonal allergies. Get relief for your toughest allergy symptoms. Allegra (Fexofenadine Hcl) may treat allergy, side effects, dosage, drug interactions, warnings, patient labeling, reviews, and related medications including drug comparison. Find patient medical information for Fexofenadine (Allegra) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Fexofenadine is an antihistamine medication used in the treatment of allergy symptoms such as allergic rhinitis and urticaria. [10] It is a common over-the-counter medication available under many brand names (including Allegra), as well as a generic drug. [11] Therapeutically, fexofenadine is a selective peripheral H 1 blocker.