Bioequivalence and Bioavailability Forum

Dear both,

I’m aware that both the FDA (in a guidance) and the EMA (in current practice) ask for measurement in serum. We all know that serum (or plasma) concentrations are a surrogate of the concentrations at the site of action (which in general is not accessible).
However, Fe stimulates the production of erythrocytes in the bone marrow (hey, the site of action!) of Fe-deficient patients. In my understanding measuring in whole blood would be more reasonable.
Just my 2 ¢.

On another note using stable isotope labelled products (⁵⁷Fe and/or ⁵⁸Fe) could help in distinguishing endo­genous from dosed Fe.