Bioequivalence and Bioavailability Forum

Salam Loky do,

❝ […] participants are both males and females, should the ratio between them be 1:1 …

The FDA requires „subjects from the general population”; hence ~1:1. Though I have seen studies in males only as well. Possibly the ANVISA requires that as well.
AFAIK, in other jurisdictions there are no rules.

❝ … or any ratio is accepted, …

See above. I once saw a study were the protocol stated “females and males” and the CRO recruited one female and 15 males. The study was accepted by European agencies but it looked stupid.

❝ … also for randomization procedure is there any special requirements in case both included?

See this thread and R-code for stratification there. IMHO, in crossover designs it does not make sense. Do we have “sex” as a factor in the model? No. Do we want to demonstrate BE separate for females and males? Generally not. If yes, we would have to (at least) double the sample size.
Parallel designs are another story, of course. Females/males should be evenly assigned to treatment groups.