The binding of drugs to hepatocytes and its relationship to physicochemical properties.

The binding of 17 drugs to rat hepatocytes has been determined using equilibrium dialysis in combination with metabolic inhibitors and a kinetic model for the binding and dialysis processes. Metabolic inhibitors were used to retard the main routes of metabolism such that the half-life for turnover of the drugs was comparable to or greater than the time scale of the equilibrium dialysis process. Further experiments were carried out to determine the kinetics of diffusion of the compounds across the dialysis membrane and the observed extent of binding to hepatocytes. Knowledge of the rate of metabolism of the drugs in the presence of the inhibitors, the kinetics of the dialysis process, and the observed extent of binding was then used with a kinetic model of the system to give true free fractions of the drugs in live hepatocytes. Further studies show that, for this set of compounds, there is no significant difference in the extent of binding to live or dead hepatocytes. The extent of hepatocyte binding is correlated with lipophilicity, and the best model for binding uses log P for basic compounds and log D(7.4) for acidic and neutral compounds. Hepatocyte binding is also demonstrated to be highly correlated with microsome binding.