Application of moment analysis to nonlinear drug disposition described by the Michaelis-Menten equation.

An equation for the mean residence time (MRT) of drug in the body is derived for the system where drug is injected intravenously into a one-compartment model and eliminated by a single, capacity-limited process. This MRT is a complex function of dose, volume, Vm, and Km but degenerates into the classical volume/clearance expression under limiting low-dose conditions (Km much greater than C0). The equation was validated by comparison of the MRT obtained by direct calculation versus numerical area estimation for simulated data. The equation may be useful analytically in the estimation of the fundamental Michaelis-Menten parameters, Vm and Km, from experimental data.