Abstract

The disposition of atorvastatin, cerivastatin, and indomethacin, established substrates of rat hepatic basolateral uptake transporters, has been evaluated in suspended rat hepatocytes. Cell and media concentration-time data were simultaneously fitted to a model incorporating active uptake, permeation, binding, and metabolism. Use of the model to estimate the ratio of intracellular to extracellular steady-state free drug concentrations demonstrated the strong influence of active uptake on the kinetics of atorvastatin (18:1) and cerivastatin (8:1), in comparison with indomethacin (3.5:1). Indomethacin, however, was shown to have a higher uptake clearance (599 ± 101 μl/min/10⁶ cells) than atorvastatin (375 ± 45 μl/min/10⁶ cells) and cerivastatin (413 ± 47 μl/min/10⁶ cells). The high passive permeability of indomethacin (237 ± 63 μl/min/10⁶ cells) clearly negated the effect of the active transport on the overall disposition. An analogous physiological model was constructed that allowed prediction of the in vivo pharmacokinetics, including the free intracellular concentration in liver. Hepatic clearance was well predicted by the model, in contrast to predictions based on standard methods. Volume of distribution was well predicted for indomethacin and predicted reasonably for atorvastatin and cerivastatin and higher than might be expected for an acid compound. Furthermore, the terminal half-life predictions for all three compounds were within 2-fold of the observed values. The ability to estimate the free-intracellular hepatic concentration of uptake substrates has major benefits in terms of predicting pharmacokinetics, potential CYP-mediated drug-drug interactions, and efficacy of hepatically targeted therapeutics.