Bioequivalence and Bioavailability Forum

Dear velupharm!

❝ What actually I meant is the difference between measured and quantifiable concentration not quantified concentration.

❝

❝ Especially for longer halflife drugs, sometimes we may not capture adequately say 4-5 halflives (considering a non-truncated approach),despite a highly sensitive bio analytical method and in such cases whatever concentration we have captured with the last may not actually represent in AUC(0-last). In that case the last measured concentration shall not represent last quantifiable concentration

Perhaps I am a little bit slow-brained today (still not getting your point).
In my opinion to be measured (=quantified) a concentration of course has to be quantifiable (≥LLOQ and ≤ULOQ) = within the validation range of the method.
If you ‘see something’ in the chromatogram (≥LOD and <LLOQ) you cannot measure it within given limits of accuracy and precision.
Tlast is defined as the time point of the last quantified concentration (within a particular profile).
This is part of a never-ending debate between analysts and phamacokineticist. The former want to report data below the LLOQ simply as 'BLQ' (or if they are liberal even distinguish between 'BLQ' and 'BLD', but never come up with a numeric value), wheras the latter want all possible numbers, irrespective of accuracy/precision (‘we don't care about error - we model it’).
In the field of BA/BE regulators definitely expect us to follow the analyst’s viewpoints.

Have a look at Azim Karim’s plot from David Bourne's PK/PD-list (also giving an explanation of Pharsight's 'invention' AUCall, which sometimes > AUCinf).

❝ Also I would like to make it clear, whatever words I have used (Confused), shall not mean to criticise or comment particular person. If somebodies feelings have been hurted, kinly pardon me.

No, no; confusion is a very creative state of mind and highly appreciated!