Bioequivalence and Bioavailability Forum

❝ Is anyone aware of the guidelines for truncation of AUC at 72 hrs for modified release products having longer half life.

I don’t know any. If IR is concerned long half life is irrelevant for truncation (see EMA’s GL); it’s high time for the FDA to revise their guidance. The 72 hours are based on the longest passage time of a formulation in the GIT.
If the MR formulation is DR IMHO truncation should be applicable as well.
For CR you might observed flip-flop PK – terminal phase represents absorption or is at least influenced by it. Personally I would be very wary to even use AUC_t as the main metric. I would rather use AUC_∞ and aim for an extrapolated area of well below 20%.