Bioequivalence and Bioavailability Forum

Dear all
I would like to perform a drug-drug interaction investigation performed as a open, randomized, three-period, cross-over trial in healthy volunteers in order to assess the relative bioavailability of drug1 and drug2 given either alone or in combination:

Treatment A: drug1+drug2 given as a FDC
Treatment B: drug1 given as a mono product
Treatment C: drug2 given as a mono product

In case linear PK applies for drug1 and drug2 a single-dose study is sufficient, otherwise I need to investigate steady state PK, right?

Background Information:
drug1 is extensively metabolised by the liver to inactive metabolites, 50% of drug2 is metabolised by the liver to inactive metabolites which are then excreted by the kidneys. The remaining 50 % is excreted by the kidneys in an unmetabolised form. Since the same route of elimination is partly used there could be a kind of competition. Could this be detected after single dose administration or do you need staedy state PK?

Looking forward to your feed back.
Kind regards
Dr_Dan