Effect of oral contraceptives (OCS) on drug metabolizing enzymes (DMES) as measured by the validated cooperstown 5+1 cocktail (5+1)

Limited Sampling Strategy of S-Warfarin Concentrations, but Not Warfarin S/R Ratios, Accurately Predicts S-Warfarin AUC during Baseline and Inhibition in CYP2C9 Extensive Metabolizers

S-warfarin area under the concentration-time curve (AUC(0- infinity )) and clearance are used as measures of cytochrome p450 (CYP) 2C9 activity. In addition, warfarin S/R ratios are used to assess CYP2C9 activity. The determination of S-warfarin AUC(0- infinity ) requires multiple blood samples. Limited sampling strategy (LSS) is a validated technique that estimates AUC(0- infinity ) using limited blood samples. The objective of this study was to evaluate LSS of S-warfarin concentrations and warfarin S/R ratios to predict S-warfarin AUC(0- infinity ) during CYP2C9 baseline activity and inhibition with fluvastatin. Fifty-one healthy subjects, genotyped as CYP2C9 extensive metabolizers, were administered oral warfarin 10 mg. Blood samples were collected over 96 hours. S-warfarin AUC(0- infinity ) equations were derived from a training set of 20 subjects using multiple linear regression. Validation of the equations used data from the remaining 31 subjects. All derived equations were within acceptable limits for measures of bias and precision. Single-point and two-point S-warfarin concentrations, but not warfarin S/R ratios, were predictive of S-warfarin AUC(0- infinity ) during CYP2C9 baseline activity and inhibition. No correlation was observed between CYP2C9(*)1/(*)1 and (*)1/(*)2 genotypes and either S-warfarin concentrations or warfarin S/R ratios. The equation using two-point S-warfarin concentrations at 24 and 48 hours was the most accurate predictor of S-warfarin AUC(0- infinity ). LSS using S-warfarin concentrations is an efficient and accurate technique to evaluate S-warfarin AUC(0- infinity ) when using warfarin as a CYP2C9 probe drug.

“Cocktail” Approaches and Strategies in Drug Development: Valuable Tool or Flawed Science?

There is an increasing interest in the simultaneous administration of several probe substrates to characterize the activity of multiple drug-metabolizing enzymes, the so-called "cocktail" approach. However, this method remains controversial and is being investigated more extensively. No general consensus has emerged on the applicability of this approach in clinical investigation and during drug development. The objective of the article is to review this important yet specialized technique, as well as its merits, drawbacks, and potential application in drug development. Among the two-, three-, four-, five-, and six-drug in vivo cocktails previously evaluated in humans, a variety of substrate probe combinations have been studied. Some probe combinations have been validated not to interact in vivo and have been useful in characterizing drug-drug interaction potential and metabolic enzyme induction in humans. For drug candidates that affect two or more in vitro pathways or are potential gene inducers, the use of a cocktail approach may facilitate the rapid delineation of the drug candidate's drug interaction potential. It may also offer the potential of providing clear guidance on safely conducting larger clinical studies and limiting comedication restrictions to only those likely to be clinically relevant.

Lack of weight-based dose dependency and intraindividual variability of omeprazole for CYP2C19 phenotyping

To determine if dose dependency occurs with 2 weight-based single doses of omeprazole in a phenotyping study, as well as to quantitate 3-month intraindividual variability of CYP2C19 activity, 24 Caucasian subjects with body weights from 45 to 66 kg and 67 to 90 kg received single oral 30-mg and 40-mg doses of omeprazole, respectively. Female subjects were phenotyped during the mid-follicular and mid-luteal phases of their menstrual cycles for 3 complete cycles. Male subjects were phenotyped every 14 days for 12 weeks. Subjects with a body weight between 45 and 66 kg received an additional 40-mg omeprazole single dose on visit 7. The 2-hour postdose plasma concentration ratio of omeprazole to 5-hydroxyomeprazole was used as a measure of CYP2C19 activity. The percent coefficient of variation (CV%) of omeprazole phenotyping ranged from 6.3% to 51.3% (median = 18.5%, interquartile range = 14.8%-23.5%). Weight-based single doses of omeprazole for CYP2C19 phenotyping did not exhibit dose dependency. Therefore, a weight-based approach may improve the quantitation of omeprazole/metabolites.