Metabolic pathways of the topical glucocorticoid budesonide in man.

The metabolic pathways of budesonide[(22RS)-16 alpha, 17 alpha-butylidenedioxy-11 beta, 21-dihydroxypregna-1,4-diene-3,20-dione] in human liver 9000g supernatant fraction were studied. A comparison was made between the in vitro metabolite pattern and the metabolite pattern in plasma obtained after iv administration of tritiated budesonide to man. No qualitative difference could be found, which indicates that the in vitro model is useful to predict results in vivo. The two major metabolites formed in vitro were identified by HPLC and mass spectrometry as 6 beta-hydroxybudesonide and 16 alpha-hydroxyprednisolone. Loss of the acetal group was not observed when desonide (11 beta,21-dihydroxy-16 alpha,17 alpha-isopropylidenedioxy-pregna-1,4-diene-3,20-dione) was incubated with human liver 9000g supernatant fraction. Neither could 16 alpha-hydroxyprednisolone be detected after incubation of the (22S)-epimer of budesonide with the same medium. The cleavage of the acetal moiety is therefore suggested to be the result of a substrate-selective metabolic pathway.