I'm having a disagreement with a DMPK colleague on the proper way to use Phoenix WinNonLin and I'm hoping others on the forum can provide some clarity. The disagreement is regarding the appropriate way to perform nca analysis for *single-dose* iv PK data (with plasma conc data from 0-24 h) using WinNonLin.
My colleague is adamant that the tau parameter should be set to 24h (since that is the last time-point measured) and that CLss is the appropriate clearance parameter to report and use from the output.
I suggest that for single-dose analysis, the tau parameter should be left blank and the appropriate clearance parameter to report/use is CL_obs. My understanding is that setting tau and using the CLss output parameter is only appropriate if your input data is from a multiple-dosing scenario.
Am I right or wrong here?
Assuming I am correct, what are the potential ramifications of my colleague consistently calculating and reporting only steady-state CLss (and Vss, etc.) values for all single-dose PK experiments?