Allegra (fexofenadine) and hives. Hello, we commonly use Allegra (fexofenadine) to treat hives or urticaria. This is a helpful medication because of the lack of sedation. Even at twice the normal recommended dosage. So it is unlikely to cause hives but you can have an allergy to antihistamines that could lead to the development of hives. That would be most unlucky.