Bioequivalence and Bioavailability Forum

Dear velupharm!

❝ [...] if we have the intrasubject CV of the same drug but of a

❝ different strength [...], can that be considered for calculation

❝ of sample size?

In principle yes. Generally the impact of analytical variability (which may be a little higher at lower concentrations) is negligible compared to biological variability, therefore I would not bother using the CV from the 40 mg study for the planned 20 mg study.

Another point is the variability of the CV between studies. To be on the safe side, you may consider using not the calculated value, but an upper confidence interval. For details have a look at this post.

If you overestimate the CV, only money is lost (you are gaining power, but still demonstrate BE), but if you understimate the CV, both time and money is lost, because you have to repeat the study...