Bioequivalence and Bioavailability Forum

Dear John
According to CPMP/QWP/EWP/1401/98 Rev. 1 AUC truncated at 72 h may be used as an alternative to AUC(0-t) for comparison of extent of exposure as the absorption phase has been covered by 72 h for immediate release formulations. A sampling period longer than 72 h is therefore not considered necessary for any immediate release formulation irrespective of the half life of the drug. If you use a cross-over design you have to be sure that you do not include slow metabolizers leading to a drug half life of >150 days, otherwise you might have to discuss carry-over effects.
Regarding intra-subject variability, as long as you decide to conduct a parallel design pilot study your sample size would be just a guess and not calculated estimate. I suggest to run the pilot study in a cross-over design and the pivotal study in a parallel design. This will take the same time for both studies as you planned vice versa but you would have more reliable data from the pilot study to plan the pivotal study.
I hope this helps.
Kind regards
Dan