Bioequivalence and Bioavailability Forum

¡Hola Javier!

❝ I was wondering about how to calculate the steady state of a drug when you have two different values of half life

See this post (especially the last sentence) and the warfarin example (slides 21–22).
If you extrapolate from SD to MD you have to rely on assumptions (linear PK, no saturation/induction/inhibition/capacity-limited excretion).

❝ (If I understand correctly the steady state of a drug takes 3-5 half lives)

It depends on how one defines sufficiently ‘close’ to true steady state (at t = ∞!). For a one-compartment model, IV administration

i  % SS
1  50
2  75
3  87.5
4  93.75
5  96.875

where i = number of half lives and % SS = 100(1 – ½ⁱ ). For EV (and more important: other models) this approach is only approximate.
Coming back to your OP: I would trust the results of the MD study’s PopPK-model more than the SD study’s results derived by NCA.