You might find this to be informative:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886486/
From the article: "The hydrocortisone enema is absorbed to some extent; the manufacturer has reported an absorption rate of 40%. In other words, if the enema contains 100 mg of hydrocortisone, then there is a systemic exposure of 40 mg, which is the equivalent of 10 mg of prednisone."