Reasons? [Study As­sess­ment]

posted by dshah – India/ United Kingdom, 2021-08-24 12:06 (61 d 20:36 ago) – Posting: # 22538
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Hi Helmut

I have following thoughts w.r.t. to my points.

1. Change in subject will cause change in concentration. Even MVR of many regulatory and ISR also permits ~15% variation at Cmax point. The Cmax is generally variable than AUC. So if the ratio difference is +/- 15%, the discussion shall be of no point. But still may point out that there is difference.

2. BA method and same instrument needs to be mentioned. It could have impact.


» » 3. Same Internal standard batch? Change in internal standard changes height and thus ultimately concentration.
»
» Given, the IS response might be different. However, even if calibrators and QC samples are prepared with, say, an IS of just 50% of the declared content in one of the studies, the back-calculated concentrations should be similar and therefore, the T/R-ratios.

Although, it sounds odd, Even for NTI- with same CRO- Method-Instrument; I have witnessed change in concentration with just change in IS batch. It may have similar T/R but even there was difference in T/R.

I hope this may help.
Regards,
Dshah

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