PT  - JOURNAL ARTICLE
AU  - Ken Korzekwa
AU  - Donald Tweedie
AU  - Upendra A. Argikar
AU  - Andrea Whitcher-Johnstone
AU  - Leslie Bell
AU  - Shari Bickford
AU  - Swati Nagar
TI  - A Numerical Method for Analysis of In Vitro Time-Dependent Inhibition Data. Part 2. Application to Experimental Data
AID  - 10.1124/dmd.114.058297
DP  - 2014 Sep 01
TA  - Drug Metabolism and Disposition
PG  - 1587--1595
VI  - 42
IP  - 9
4099  - http://dmd.aspetjournals.org/content/42/9/1587.short
4100  - http://dmd.aspetjournals.org/content/42/9/1587.full
SO  - Drug Metab Dispos2014 Sep 01; 42
AB  - Time-dependent inhibition (TDI) of cytochrome P450 enzymes is an important cause of drug-drug interactions. The standard approach to characterize the kinetics of TDI is to determine the rate of enzyme loss, kobs, at various inhibitor concentrations, [I], and replot the kobs versus [I] to obtain the key kinetic parameters, KI and kinact. In our companion manuscript (Part 1; Nagar et al., 2014) in this issue of Drug Metabolism and Disposition, we used simulated datasets to develop and test a new numerical method to analyze in vitro TDI data. Here, we have applied this numerical method to five TDI datasets. Experimental datasets include the inactivation of CYP2B6, CYP2C8, and CYP3A4. None of the datasets exhibited Michaelis-Menten–only kinetics, and the numerical method allowed use of more complex models to fit each dataset. Quasi-irreversible as well as partial inhibition kinetics were observed and parameterized. Three datasets required the use of a multiple-inhibitor binding model. The mechanistic and clinical implications provided by these analyses are discussed. Together with the results in Part 1, we have developed and applied a new numerical method for analysis of in vitro TDI data. This method appears to be generally applicable to model in vitro TDI data with atypical and complex kinetic schemes.