Renwick et al., 2000); (10) Interindividual variability of enzymes in human; (11)
potential complication due to renal or hepatic impairment; and (12) interactions
with dietary ingredients.
16.6 Conclusion
In vitroevaluation of NCEs as inhibitors of CYP activity at early stages of drug
development is crucial for prediction of DDI potential in human. The chapter
provides theoretic background of enzyme inhibition kinetics, experimental
approaches for determination of kinetic parameters for both reversible and
mechanism-based CYP inhibition, and individual CYP inhibition assays,
particularly with LC/MS/MS analysis from a perspective of pharmaceutical
industry. These allow adaptation of the system to determine detailed enzyme
kinetics and inhibition parameters in an HTS fashion for drug metabolism
scientists. The enzyme kinetic values obtained from the assays can be used to
assess the potency of the inhibitors, to predict DDI potential in clinic, to drive
decision-making on drug development at early stages and to direct informed
planning of clinical DDI studies. In addition to the prediction fromin vitro
inhibition data, drug interaction studies in animals, when coupled with the
correspondingin vitrostudies, can be of great benefit in understanding the
relationships betweenin vitro inhibition andin vivo PK-based DDIs and
provide accuracy of the prediction.
Acknowledgment
The authors would like to thank Ping Lu, Regina Wang, Chris Kochansky,
Ryan Norcross, Rich Edom, Ken Korzekwa, Juinn Lin, Tom Baillie (Merck
Research Laboratories, West Point, PA19486, USA), Ming Yao (Bristol-
Myers Squibb Pharmaceutical Research Institute, Princeton, NJ 08543, USA)
for their contribution and comments.
References
Atkinson A, Kenny JR, Grime K. Automated assessment of time-dependent inhibition
of human cytochrome P450 enzymes using liquid chromatography-tandem mass
spectrometry analysis. Drug Metab Dispos 2005;33:1637–1647.
Austin RP, Barton P, Cockroft SL, Wenlock MC, Riley RJ. The influence of nonspecific
microsomal binding on apparent intrinsic clearance, and its prediction from
physicochemical properties. Drug Metab Dispos 2002;30:1497–1503.
Azie NE, Brater DC, Becker PA, Jones DR, Hall SD. The interaction of diltiazem with
lovastatin and pravastatin. Clin Pharmacol Ther 1998;64:369–377.
Backman JT, Olkkola KT, Aranko K, Himberg JJ, Neuvonen PJ. Dose of midazolam
should be reduced during diltiazem and verapamil treatments. Br J Clin Pharmacol
1994;37:221–225.
538 ANALYSIS OFIN VITROCYTOCHROME P450 INHIBITION