Bioequivalence and Bioavailability Forum

❝ we are trying to built a biowaiver justification for the lowest strength of a products.

If I understand correctly you have BE study for highest strength and want to justify biowaiver for lower strenght(s). However this lower strength does not fullfil general biowaiver criteria (as described in 4.1.6 of BE guideline) so you consider BCS-based biowaiver instead.
Such approach is theoretically possible, assuming that drug substance is considered as highly soluble i.e. highest single dose is completely dissolved in 250 ml of buffers accross 1 - 6.8 pH range. This in turn depends on posology of given strenght. I think there are 2 scenarios. Let's say the product is of 10 mg and 5 mg:
1 - you have same posology for both strengths i.e. highest dose is 10 mg and patient can take it either as 1x10 or 2x5 mg. Then 10 mg has to be proven as highly soluble in order to apply BCS-based biowaiver for 5 mg
2 - posology is different i.e. for 5 mg strenght - 5 mg is highest dose (i.e. you cannot use as multiplication for higher dose), and for 10 mg - 10 mg. Then it would be suffcient to prove high solubility for 5 mg of active substance to apply BCS-based biowaiver for this strength.
Hope I helped.
Best regards,
Łukasz