Effect of plasma protein binding on drug disposition in muscle tissue: application of statistical moment analysis and network theory to in situ local single-pass perfusion system.

The local disposition characteristics of mitomycin C (MMC) and five lipophilic prodrugs in rabbit hind leg muscle were examined using an in situ single-pass perfusion experiment. Test compounds inputted into a perfusion line as a rectangular function (unit pulse) were perfused with or without albumin and their outflow patterns were analyzed by statistical moment analysis. In interpretation of statistical moment parameters, the well-stirred model was applied to the local perfusion system based on the plate theory of a chromatographic system and some general pharmacokinetic parameters (the disposition parameters) were derived from the moments. A new theory which elucidates the relationships among the moments for plasma protein binding, unbound (free), and total drug fraction was established based on network theory. Using this system, the following conclusions were made for mitomycin C and its five lipophilic derivatives: (i) In the absence of albumin, an increase in lipophilicity led to an increase in organ clearance and distribution volume; (ii) drug bound to albumin did not transfer to the extravascular space; (iii) in the presence of albumin, an increase in lipophilicity results in a decrease in clearance.