IC50-based approaches as an alternative method for assessment of time-dependent inhibition of CYP3A4.
The predictive utility of two in vitro methods (empirical IC(50)-based and mechanistic k(inact)/K(I)) for the assessment of time-dependent cytochrome P450 3A4 (CYP3A4) inhibition has been compared. IC(50) values were determined at multiple pre-incubation time points over 30 min for five CYP3A4 time-dependent inhibitors (verapamil, diltiazem, erythromycin, clarithromycin, and azithromycin). The ability of IC(50) data obtained following pre-incubation to predict k(inact)/K(I) parameters was investigated and its utility was assessed relative to the conventional k(inact)/K(I) model using 50 reported clinical drug-drug interactions (DDIs). Models with either hepatic or hepatic with intestinal components were explored. For low/medium potency time-dependent inhibitors, 81% of the predicted k(inact)/K(I(unbound)) from IC(50) data were within an order of magnitude of the actual values, in contrast to 50% of potent inhibitors. An underprediction trend and > 50% of false-negatives were observed when IC(50) data were used in the DDI hepatic prediction model; incorporation of the intestine improved the prediction accuracy. On the contrary, 86% of the DDI studies were predicted within twofold using k(inact)/K(I) mechanistic approach and the combined hepatic and intestinal model. Use of the empirical IC(50) approach as an alternative to the mechanistic k(inact)/K(I) model for in vivo DDI prediction is limited and is best restricted to preliminary investigations.
School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
Howard J
HJ
Burt
Aleksandra
A
Galetin
J Brian
JB
Houston
D019540:Area Under Curve; D051544:Cytochrome P-450 CYP3A; D065692:Cytochrome P-450 CYP3A Inhibitors; D004353:Drug Evaluation, Preclinical / Q000379:methods*; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008954:Models, Biological; D013997:Time Factors
D065692:Cytochrome P-450 CYP3A Inhibitors; D004791:Enzyme Inhibitors; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human