Bioequivalence and Bioavailability Forum

Dear All,

I could not find in the guidelines that what should be done regarding the following issue.
You had made a given formulation and it passed the biostudy. No problem till this point. :)
However, the API supplier has changed and the new API is quite different from the previous one (impurity profile, residual solvents, etc.).
The new API is also acceptable but DIFFERENT.
Can I use the results of the biostudy conducted with the preceding API?
Do I have to prove that the differences between the API would not alter significantly the bioavailability (and the safety) of the API?
If so, how?
If a slight difference is acceptable, what is the extent?

Thanks in advance!

Best regards,
Laszlo