Structural identifiability of "first-pass" models

Definition of a physiologic pharmacokinetic model of cutaneous drug distribution using the isolated perfused porcine skin flap

A physiologic pharmacokinetic model describing drug disposition in the isolated perfused porcine skin flap (IPPSF) is derived. The IPPSF is well suited for experimental studies of dynamic drug distribution into skin because arterial and venous drug fluxes can be continuously monitored. The system parameters of the model are uniquely identifiable and describe the cutaneous efflux profile as a function of arterial input flux and tissue partitioning or extraction. This model allows experimental results obtained from an in vitro preparation to serve as a quantitative input to an in vivo, whole animal pharmacokinetic system. Experimental infusion applications of the cancer chemotherapeutic agents cisplatin and carboplatin and the antimicrobials tetracycline and doxycycline are reported herein.

The problem of model indistinguishability in pharmacokinetics

The problem of model indistinguishability is introduced in the context of linear compartmental models in pharmacokinetics. The two most widely used methods of analyzing model indistinguishability are described. It is shown that as the number of compartments increases, one approach, based on the Laplace transforms of the observations, although conceptually simple, can result in very large numbers of candidate models to be examined for indistinguishability, while the other approach, based on similarity transformations, although systematic, often results in very difficult algebraic expressions. These problems can be eased by the use of some simple geometrical rules, used at the outset of an indistinguishability analysis. The approach is illustrated by application of two 2-compartment drug, 2-compartment metabolite models.