Fexofenadine
Fexofenadine is an over-the-counter second-generation antihistamine used in the treatment of various allergic symptoms. It is selective for the H1 receptor, carries little-to-no activity at off-targets, and does not cross the blood-brain barrier - this is in contrast to previous first-generation antihistamines, such as [diphenhydramine], which readily bind to off-targets that contribute to side effects such as sedation. Fexofenadine is the major active metabolite of [terfenadine] and is administered as a racemic mixture in which both enantiomers display approximately equivalent antihistamine activity.