An area function method for calculating the apparent elimination rate constant of a metabolite

A simple method for determination of the apparent elimination rate constant of a metabolite (km) has been developed. This procedure requires calculation of area intervals under the plasma concentration-time curves of the parent drug and its derived metabolite. The method has been evaluated and compared with the Chan moment method using both errorless and errant data. The approach is accurate for various ratios of elimination rate constants of drug and metabolite, allows several values of km to be averaged, but works best using data prior to the metabolite tmax.