Brand Name: Allegra, Allegra Allergy 12 Hour, Allegra Allergy 24 Hour, Children's Allegra Allergy, Mucinex Allergy. Generic Name: fexofenadine. Drug Class: Antihistamines. What Is Fexofenadine and How Does It Work? Fexofenadine is an antihistamine used to relieve allergy symptoms such as...