MRT was derived as the mean value of the continuously distributed random variable residence time. Provide that elimination kinetics is linear and that elimination takes place exclusively from the central compartment, MRT can be calculated from the ratio AUMC/AUC. In this case, MRT is a drug (and formulation) related constant MRT may also be determined when the elimination kinetics is nonlinear. The meaning of those MRT values, however, remains limited because they depend on the dose applied.