Curve-fitting in pharmacokinetics--a comparison between gamma- and biexponential fits

Seven sets of plasma concentration-time data were fitted to both a conventional biexponential equation and a gamma equation. The values of clearance (CL) and mean residence time (MRT) were calculated from the fitted parameters and compared with the values calculated by the trapezoid rule. Both the biexponential and gamma equations provided adequate fits to the data. The values of CL and MRT calculated from the biexponential fits correlated very closely with the values calculated by the trapezoid rule, but there were large discrepancies between the values calculated from the gamma fits and the trapezoid rule. The biexponential model appears to be less sensitive to scatter in the data.