Mean residence time

The definition of mean residence time in the strict sense of mathematical statistics is deduced. It is demonstrated that the area-normalized concentration time curve is an estimate of the probability density function for residence times of drug molecules in the pharmacokinetic system, provided that the area under the concentration-time profile is proportional to the total amount eliminated from the system. Criticisms (8) on the determination of the mean residence time are refuted. The linearity of pharmacokinetic systems is defined, based on the statistical interpretation of these systems.