Bioequivalence and Bioavailability Forum

Hello.

We conducted a crossover 2x2 study of Levothyroxine 25ug* and found a significant sequence effect (considering a significance level of 10%). According to ANVISA guidelines, a siginifcant sequence effect can only be desconsidered if the following criteria are met:
“i. The study is a single dose study;
ii. The study envolves only healthy subjects;
iii. The drug is not an endogenous substance;
iv. The washout period was adequate and the pre dose samples do not present any level of the drug for all subjects;
v. The study satisfies all scientific and statistic criteria.
Under others circustances, the study must be redone.” (my translation)
I think it is worthy mentioning that ANVISA requires a basal correction where we have to collect three blood samples prior to the dose, and "correct" all values using the mean concentration of those three points (Quantified value - Mean basal concentration= Corrected Concentration).
So, considering that, the study is useless, even though it was concluded the bioequivalence. What we can’t figure out is where the problem is. The washout period was 70 days (the FDA’s draft guidance on Levothyroxine suggests 35 days), the same as other 3 studies of Levothyroxine that we conducted with the same (or pretty close) dosage, between 600 – 630 ug. So it seems to me that this is not a true carry-over effect that the regulatory agencys fear so much. What are your thoughts on that? I mean, would you guys extend even more the washout period? Or even: can that sequence effect be somehow justified to be ignored?

*At first I mistyped the strenght, where it was 65 ug it should say 25ug.