My father, age 67, is suspect of having diverticulitis. He is scheduled to have a cat scan with iodine/barrium contrast, however, he is severly allergic to idoine. He was give medication to block, I guess called a "prep" to handle the idodine allergy. Does this prep work most of the time. He is worried about dying from the cat scan, but is more concerned about getting diagnosed and he had not had a bowel movement is two weeks.