First-order and pseudo-first-order elimination kinetics.

There is evidence that, for a number of chemicals, the elimination characteristics during bioconcentration do not follow monophasic first-order kinetics. In the first part of the present communication, a simple mathematical formula is presented that allows a clear-cut distinction between monophasic (pseudo-) and first-order and morephasic or higher-order elimination processes. The second part gives the mathematical description of a simple monophasic pseudo-first-order two-compartment model, which allows a quantitative kinetic analysis in the case of both initial compound and metabolite elimination.