title: Midazolam and cortisol metabolism before and after CYP3A induction in humans.
abstract: BACKGROUND
  CYP3A is responsible for the metabolism of numerous endogenous and exogenous compounds. Several substrates of CYP3A have been investigated to assess the CYP3A-metabolizing capacity of an individual in an attempt to predict the rate of metabolism of other CYP3A substrates. Two such tests of CYP3A activity are the midazolam plasma clearance after its intravenous administration and the 6beta-OH cortisol urinary ratio. Possible correlations between these 2 tests were investigated before and after treatment with rifampin in a group of healthy volunteers.
  
  
  METHODS
  Pharmacokinetic parameters of midazolam and 6beta-OH cortisol urinary ratio were evaluated in 8 volunteers before and after 6 days treatment with rifampin, a potent inducer of CYP3A, and after cessation of rifampin treatment.
  
  
  RESULTS
  Midazolam systemic clearance and the 6beta-OH cortisol urinary ratio were significantly higher at Days 7 and 10 than at Day 0. There was a strong positive correlation between these 2 parameters (r = 0.70, p < 0.001). In contrast, no correlation was observed between the ratio of the AUCs of 1'-OH midazolam vs. midazolam (AUC0-1(1'-OH)/AUC0-t(MDZ)) or the ratio of plasma concentration of 1'-OH midazolam vs. midazolam (C30 min(1'-OH)/C30 min(MDZ)) and the 6beta-OH cortisol urinary ratio (r = 0.05, p = 0.82; r = 0.04, p = 0.88, respectively). Considering only data obtained before or after treatment with rifampin, however, no correlation was observed between midazolam systemic clearance and the 6beta-OH cortisol urinary ratio.
  
  
  CONCLUSIONS
  These data demonstrate that there is a strong positive correlation between systemic midazolam clearance and 6beta-OH cortisol urinary ratio before and after induction. This suggests that the 6beta-OH cortisol urinary ratio test is a non-invasive alternative to the use of systemic midazolam clearance for monitoring the time-course of CYP3A induction.
authors.affiliation: Unité de Pharmacocinétique, Métabolisme, Nutrition et Toxicologie, Ecole de Santé Publique, Université catholique de Louvain, Brussels, Belgium.
authors.forename: S L
authors.initials: SL
authors.lastname: Eeckhoudt
authors.forename: J P
authors.initials: JP
authors.lastname: Desager
authors.forename: A R
authors.initials: AR
authors.lastname: Robert
authors.forename: I
authors.initials: I
authors.lastname: Leclercq
authors.forename: R K
authors.initials: RK
authors.lastname: Verbeeck
authors.forename: Y
authors.initials: Y
authors.lastname: Horsmans
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001189:Aryl Hydrocarbon Hydroxylases; D015415:Biomarkers / Q000032:analysis; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D018757:GABA Modulators / Q000493:pharmacokinetics*; D006801:Humans; D006854:Hydrocortisone / Q000031:analogs & derivatives* / Q000652:urine*; D008297:Male; D008874:Midazolam / Q000493:pharmacokinetics*; D008875:Middle Aged; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism*; D011237:Predictive Value of Tests; D012293:Rifampin / Q000494:pharmacology*
chemical_list: D015415:Biomarkers; D004791:Enzyme Inhibitors; D018757:GABA Modulators; C001380:6 beta-hydroxycortisol; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D008874:Midazolam; D012293:Rifampin; D006854:Hydrocortisone