Following absorption, budesonide is subject to high first pass metabolism (80% to 90%). In vitro experiments in human liver microsomes demonstrated that budesonide is rapidly and extensively biotransformed, mainly by CYP3A4, to its 2 major metabolites, 6β-hydroxy budesonide and 16α-hydroxy prednisolone. The corticosteroid activity of these metabolites was negligible (less than 1/100) in relation to that of the parent compound. In vivo investigations with intravenous doses in healthy subjects were in agreement with the in vitro findings.
The responses to adrenocorticotropin challenge (., ACTH stimulation test) was studied in pediatric patients aged 8 to 17 years, with mild to moderate active Crohn’s disease in randomized, double-blind, active control study [see Clinical Studies ()] . After 8 weeks of treatment with 9 mg once daily Entocort EC or with prednisolone, administered at tapering doses starting from 1 mg/kg, the proportion of patients with normal response to the ACTH challenge was 6% in the budesonide group compared to none in the prednisolone group; the proportion of patients with morning p-cortisol of greater than 5 mcg/dL was 50% in the budesonide group compared to 22% in the prednisolone group. The mean morning p-cortisol was mcg/dL in the budesonide group and mcg/dL in the prednisolone group (Table 4).