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We have a validated method for a clinical molecule and long term stability (1 year) is established. With this method we used a structural analog as an internal standard. We are thinking of re-validating this method with isotopically labeled internal standard (IS). Are we required to re-establish long term stability with this new method? Do we need to do full validation with the new IS?
Purvi
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Why would you expect stability to be affected? You validated the method, now you are bridging in a new internal standard. I believe all you would need to do is demonstrate that QC prepared with he new IS read off curves prepared with the new IS, that the LLOQ and ULOQ of the old method are achievable with the new CURVE and IS.
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There is a small risk that something in the sample could be generated over time that interferes at the monitored mass of the internal standard. One way to mitigate this risk would be that if you had any sample stored for a long time, you could either reassay it to show that nothing in the sample is generated over time. that interferes.
-Tom
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