Bioequivalence and Bioavailability Forum

Dear Stefano,

❝ ... My personal feeling is that the inclusion of the sequence effect is more strongly requested by the regulator for BE studies than for other kinds of trials.

Not necessarily so. Since the introduction of the cross-over design researchers using it have to struggle with the question of sequence effect, carry-over ... and so on. This historical burden lasts for BE studies until nowadays, although its meanwhile clear that at least carryover is avoided by proper planning of BE cross-over studies (appropriate wash-out).

Carry-over is only one explanation of the more universal term of a treatment by period interaction which can have many sources.
This interaction is prominent in cross-over studies, also Senn[2] has argued that this interaction is also of importance for parallel group studies.

❝ ... this regulatory requirement leads me to another question: which effect should we include for the analysis of a crossover design with number of periods = number of treatments > 2 (i.e., 3x3, 4x4, etc.)?

I use for such studies exactly the same ANOVA model as for the classical 2x2 crossover.

❝ ... But how the sequence effect should be interpreted in such a design?

That's is a good question. Next question, please .

Don't waste your time in considering simple models of carry-over. They all do not make sense as you know from Senn [1]. I haven't seen or used any such models of simple carry over in my career up to now (more than 30 years) and was not asked by regulators to do so in the evaluation of BE studies.

[2]S. Senn,
"Crossover Trials, degrees of freedom, the carryover problem and its dual",
Stat. Med., Vol.10, p 1361-1374