Bioequivalence and Bioavailability Forum

Hi Mehul,

❝ Can anybody please tell what may be the probable reasons behind significant (more than 20%) difference in mean Cmax concentration of Reference product of a same batch number in two different studies conducted at same CRO and on the similar kind of population but different sample size?

I guess you had also the same batch of the test? Was the AUC different as well?

❝ Is it correct to compare and expect Reference product's behavior same for all repeated studies?

A few reference products (dasatinib is an infamous example) show extreme batch-to-batch variability. However, generally batches are expected to be similar.
You could compare the references of the two studies as a paired design (assuming to period effects). For a quick estimate calculate \(\small{\widehat{PE}=PE_1/PE_2}\), with \(\small{PE_1=\frac{T}{R_1}}\) and \(\small{PE_2=\frac{T}{R_2}}\), where \(\small{R_1}\) and \(\small{PE_1=\frac{T}{R_2}}\) are the reference batches of the two studies.

❝ […] Can 6 months old (frozen) samples yield significant different results as compared to freshly analyzed study samples?

If long term storage was validated for this duration, no.