I have a fixed dose combination drug given every 12 hours (tau = 12). One of the component of the FDC has very long half-life. The t1/2 values are 21 hrs for parent compound and the 3 active metabolites are 26 hrs for metabolite A, 31 hrs for metabolite B, and 50 hrs for metabolite C.
Blood sampling was collected for 12 hrs (a dosing interval). Because of the long t1/2 of the metabolites, I was not able to estimate lamda-z to estimate AUCtau for the metabolites. However, WNL was able to calculate AUC(0-12) for them since most subjects have samples collected at 12:10 hrs (a little longer than the end time of AUC(0-12).
Can I used AUC(0-12) to report as AUCtau since AUC(0-12) and AUCtau are the same in this case.
Thanks very much for your advice!