Bioequivalence and Bioavailability Forum

Dear C_max!

An excursion into terminology first:

• Statistics, PK models → parameters
  
• NCA → PK metrics or characteristics

❝ what is the fun in reporting seconary parameters in the generic submission... we are only concerned about Cmax & AUC 90 CI. regulators evaluate this.

Help regulators in assessing the product. Sometimes rapid onset is of importance (might be a clinical claim or should be avoided due to AEs) ⇒ early exposure (FDA) or t_max (EMA and many others).
For some antibiotics the time interval above a threshold (e.g., MIC: minimum inhibitory concentration) is actually the only important one (AUC and C_max are irrelevant). In the past I have submitted studies (which were accepted in the EU), where I reversed the order: time above MIC primary, AUC & C_max only supportive. Given the new GLs (concentrating on pharmaceutical quality rather than clinical relevance), I would not dare that any more – but still report it as secondary.
If you have a delayed release formulation, t_lag might be of interest.
For pulsatile MR formulations partial AUCs might be more important than AUC_t. For instance FDA is considering following AUC-metrics for MR methylphenidate (measuring rapid onset and extended release):

• Fasting: AUC_0-3, AUC_3-24, AUC_0-∞
  
• Fed:     AUC_0-4, AUC_4-24, AUC_0-∞

❝ and in pilot study how it helps interpretation...

It helps you in understanding your product.