Numerical method analysis of the activation and time‐dependent inhibition of midazolam metabolism by ticlopidine

Abstract

Drug metabolism plays an important role in the pharmacokinetic and pharmacodynamic properties of drug candidates. In most cases, drug metabolizing enzymes (DMEs) display non‐Michalis‐Menten or atypical kinetics. Atypical kinetics includes activation, autoactivation, partial inhibition, substrate inhibition, and biphasic saturation curves. These kinetics make it difficult to obtain in vitro kinetic constants to be used for in vivo predictions of drug‐drug interactions. Numerical methods offer a unique tool to estimate improved kinetic constants. In this study, we use ordinary differential equations to model the activation and time‐dependent inactivation of midazolam (MDZ) hydroxylation by ticlopidine. Ticlopidine (TCP) is the first thioenopyridine‐based prodrug developed to inhibit platelet aggregation. Time‐dependent inactivation (TDI) assays showed both activation and partial inactivation of midazolam hydroxylation. Co‐incubation of MDZ with different TCP concentrations (0–250 μM) activated the formation of 1‐hydroxymidazolam, increasing kcat by 30%. Additional experiments are currently underway to model the observed activation and time‐dependent inactivation of CYP‐mediated metabolism of MDZ by TCP.Support or Funding InformationFunding: NIGMS grants R01GM114369 and R01GM104178.