Bioequivalence and Bioavailability Forum

❝ Thanks. Yes, PKNCA's vignette is clear. I still cannot believe that I had the false memory for so many years, and I still think I must've have read it somewhere else about the step-wise regression approach

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❝ I guess I probably should also thank myself for giving my Phoenix license to my colleague recently and was forced to use R instead of Phoenix for the first time to double check the CROs' results, otherwise I wouldn't have noticed it.

I just saw this post. For disclosure, I'm the primary author of PKNCA.

The only way that I know PKNCA's automation for lambda z estimation is different than WinNonlin is one very particular case. Both programs calculate all possible half-life estimates from third to last to the next point after Tmax. PKNCA next selects the best line by adjusted r-squared; WinNonlin next filters for negative slopes (non-increasing half-lives) then for best adjusted r-squared.

The difference is that when the best adjusted r-squared line is increasing, PKNCA will not report an automated half-life estimate. WinNonlin will report a half-life is there is any adjusted r-squared line that is decreasing. Usually, the estimated half-life would not be high-quality (the adjusted r-squared would be low, the span ratio would be low, and the percent extrapolated would be high), so as long as appropriate filtering for good values is in place, these estimates wouldn't make it to a final summary.