Hrs after a CT scan with contrast medium I developed a body rash. How long can this last.?

This is a contrast. Reaction. Notify your doctor. Take Benadryl (diphenhydramine) as directed for the rash. Must tell the technologist or doctor before you ever get dye again or you can have a severe reaction. Will need to be premedicated if you are to get dye again.
10-14 days. A single-dose drug eruption typically lasts from 10 to 14 days - but that's assuming your rash was caused by the ct contrast medium; it could be one of many other things coincidentally occurring at the same time. It would be wise to let a dermatologist examine you to confirm that you indeed have a drug eruption and not something else.