Drug distribution as a function of binding competition. Experiments with the distribution dialysis technique.

In the distribution dialysis technique each of the two dialysis chambers contains a binding system, and a drug is allowed to distribute between them. This technique was tested by using various intracellular and extracellular binder preparations over wide concentration ranges, and model drugs selected for their known binding properties. The drugs were then tested at therapeutic concentrations in standardized systems of liver homogenate (0.5 g ml-1) and whole blood (0.02 ml ml-1). The resulting intracellular/extracellular concentrations ratios were characteristic for the binding properties of the various drugs. Thus, for imipramine, a drug with strong tissue and weaker plasma binding properties, the concentration ratios were 25 for the system homogenate/buffer, 0.8 for buffer/blood, and 15 for the competitive system homogenate/blood. In experiments with homogenates from various tissues (liver, lung, kidney, intestine, brain) and blood in the standard system, the following approximate ratios were obtained: 1 for antipyrine, 2 for phenylbutazone, 14 for imipramine (but only 8 with muscle, skin and adipose tissue). These results reflect both the individual binding to intracellular and extracellular components and the tissue/blood concentration ratios in vivo. It is suggested that distribution dialysis is an in vitro method for characterizing the distribution of the drugs. It is also concluded that drug distribution is largely determined by a binding competition between tissue and blood sites.