Simultaneous assessment of CYP3A4 and CYP1A2 activity in vivo with alprazolam and caffeine

Pharmacogenetics. 1999 Dec;9(6):725-34. doi: 10.1097/01213011-199912000-00007.


Alprazolam (ALP) and caffeine (CAF) were suggested as probe drugs for the activities of CYP3A4 and CYP1A2, respectively. We investigated the disposition of oral ALP (1 mg) and CAF (100 mg) in 17 normal volunteers to establish and validate a procedure for the simultaneous assessment of CYP3A4 and CYP1A2 enzyme activity. Nine received ALP alone, ALP and CAF and CAF alone in an open three-way crossover study to test for pharmacokinetic interaction. Four received ALP after a 2-day pretreatment with ketoconazole, an inhibitor of CYP3A4, and four normal volunteers received ALP after 4 days of rifampin, an inducer of CYP3A4. AUC values of ALP and CAF administered alone were not different from AUC values when both drugs were administered combined, indicating that there is no metabolic interaction. The ratio formed of paraxanthine and CAF correlated significantly with systemic CAF clearance at 3, 4, 6, 8, 10 and 24 h. There was a strong correlation between AUC values of ALP and CAF and the plasma concentration obtained 6, 8, 10, or 24 h after ingestion of the drug. Ketoconazole and rifampin pretreatment significantly changed AUC values of ALP (mean AUC values in microg/l h: ALP = 242.2, ALP + ketoconazole = 426.2, ALP + rifampin = 28.4, ANOVA F = 17.7, P < 0.001). We conclude that ALP and CAF can be administered simultaneously for the assessment of CYP activity. Plasma concentrations 6, 8, 10, and 24 h after drug ingestion reflect AUC of ALP and CAF and therefore in-vivo CYP3A4 and CYP1A2 activity, respectively.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Alprazolam / pharmacokinetics*
  • Area Under Curve
  • Caffeine / pharmacokinetics*
  • Cytochrome P-450 CYP1A2 / metabolism*
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme Inhibitors
  • Cytochrome P-450 Enzyme System / biosynthesis
  • Cytochrome P-450 Enzyme System / metabolism*
  • Enzyme Induction
  • Enzyme Inhibitors / pharmacology
  • Female
  • Humans
  • Ketoconazole / administration & dosage
  • Male
  • Middle Aged
  • Mixed Function Oxygenases / antagonists & inhibitors
  • Mixed Function Oxygenases / biosynthesis
  • Mixed Function Oxygenases / metabolism*
  • Reference Values
  • Rifampin / pharmacology


  • Cytochrome P-450 Enzyme Inhibitors
  • Enzyme Inhibitors
  • Caffeine
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • CYP3A protein, human
  • Cytochrome P-450 CYP1A2
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Ketoconazole
  • Rifampin
  • Alprazolam