Pharmacology Kidney 22f4c9d3 The longest acting antihistaminic is A Terfenadine B Astemizole C Fexofenadine D Cetrizine High-Yield Explanation Terfenadine is a prodrug broken down to fexofenadine.so long duration of action followed by astemizole Ref: Goodman Gillman 12th ed.Pg 924.