 [ Symptoms ] i went to the er for a rash was given iv injection and ephinephrine went to dr prednisone zyrtec benedry still rash the dr said i had an allergic reaction to sulfur antibiotic i have been to the er and the dr twice i still have the rash it itches and burns in addition to the iv treatment and shot of epinephrine at the er i have been on 30mg of prednisone benadryl zyrtec [ Disease ] i have no way of confirming or disputing your allergic reaction diagnosis but i can tell you that sulfa drugs can have a very dramatic rash as a non allergic side effect and this rash can last days an allergic rash is typically very itchy hives a sulfa drug reaction common toward the end of your course of treatment does not usually itch