Send to

Choose Destination
Clin Pharmacol Ther. 2011 Jun;89(6):888-95. doi: 10.1038/clpt.2011.53. Epub 2011 Apr 13.

Evaluation of 6β-hydroxycortisol, 6β-hydroxycortisone, and a combination of the two as endogenous probes for inhibition of CYP3A4 in vivo.

Author information

Department of Pharmaceutics, University of Washington School of Pharmacy, Seattle, Washington, USA.


An endogenous probe for CYP3A activity would be useful for early identification of in vivo cytochrome P450 (CYP) 3A4 inhibitors. The aim of this study was to determine whether formation clearance (CL(f)) of the sum of 6β-hydroxycortisol and 6β-hydroxycortisone is a useful probe of CYP3A4 inhibition in vivo. In human liver microsomes (HLMs), the formation of 6β-hydroxycortisol and 6β-hydroxycortisone was catalyzed by CYP3A4, and itraconazole inhibited these reactions with half maximal inhibitory concentration (IC(50))(,u) values of 3.1 nmol/l and 3.4 nmol/l, respectively. The in vivo IC(50,u) value of itraconazole for the combined CL(f) of 6β-hydroxycortisone and 6β-hydroxycortisol was 1.6 nmol/l. The greater inhibitory potency in vivo is probably due to circulating inhibitory itraconazole metabolites. The maximum in vivo inhibition was 59%, suggesting that f(m,CYP3A4) for cortisol and cortisone 6β-hydroxylation is ~60%. Given the significant decrease in CL(f) of 6β-hydroxycortisone and 6β-hydroxycortisol after 200-mg and 400-mg single doses of itraconazole, this endogenous probe can be used to detect moderate and potent CYP3A4 inhibition in vivo.

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for Wiley Icon for PubMed Central
Loading ...
Support Center