Bioequivalence and Bioavailability Forum

Dear Vishal,

❝ Analyte response was not decreased with ISTD response.

How do you know ? You don't know the real concentrations.

❝ what are the possible reasons for obtaining low ISTD response in

❝ particular one subject compare to CC-QC ISTD response?

If you are using LC/MS/MS: my best guess would be matrix effects. Ion suppression due to... we don't know what. The problem is, you don't know whether the analyte and the IS are affected in a similar way (in which case the concentrations are not modified) or not (in which case the concentrations you calculated are inaccurate).

❝ How can we handle this subject data?

In this situation I would suggest to follow NewInPK's suggestion: change your chromatographic conditions, go for longer retention times, possibly with a gradient, and run a few samples from that subject. You may manage to get your peaks out of the ion suppression region. Alternatively, change your extraction procedure, but this requires more development work. If this works, do a partial validation with the new conditions, and run the full subject again.

By the way, are you using the same anticoagulant with your subject samples and with the CCs and QCs ?

Regards
Ohlbe