Pharmacokinetics tricks and traps: flip-flop models.

In the analysis of extra-vascular plasma concentration-time profiles, the disentanglement of influences from disposition and absorption rate influences is often challenging. This can be particularly true when absorption is considerably slower than disposition, that is, in a “flip-flop” system. The purpose of this communication is to define a pharmacokinetic flip-flop system (in a linear system) and characterize some of its properties.