They can be given orally, rectally or intravenously. Corticosteroid act to suppress the immune system by reducing the number of inflammatory cells present and also by keeping the inflammatory cells from producing chemicals that may damage the colon or perpetuate the inflammation. Corticosteroid are the most rapidly effective medications taking only a few days to reach maximal effectiveness compared to the immunomodulatory medications and aminosalicylates which take weeks to months to work maximally. Steroids are usually used in patients with mild to moderate disease which have not responded to the amminosalicylate medications. Intravenous form is used because these patients usually can not tolerate taking pills orally.
Steroids can cause suppression of the adrenal glands, and an increase risk for heart disease.
These side effects are both dose and duration dependent, that is why your doctor uses the smallest effective dose and prescribes these for the shortest time possible. Though corticosteroid can put patients with active UC into remission, their chronic usage has not been shown to be helpful in maintaining remission. The problem with its usage in UC is that it works best on inflammation present in the small intestine and right side of the colon and thus will not be useful in most patients with UC unless their whole colon is affected. Thus they help to minimize the short and long term side effects that patients on corticosteroid experience. 6-MP so essentially these medications are the same drug.