Chromatography Forum

Hi,

I'm managing HPLC assay analysis of a peptide drug and I've always worked with assay specifications such as 97.0% - 103.0% or 98.0% - 102.0% w/w. To my understanding, these limits are solely based on method uncertainty (+/- 3 sigma), which I have always accepted. However, our peptide has some degradation which theoretically will result in a lower assay value than e.g. 97.0%.

How is degradation considered when limits like 97.0% - 103.0% w/w are set in guidelines etc.? How can we incorporate both the method uncertainty and the degradation in our assay limit?

Thanks!

Is this a drug substance (API) or drug product (eg, tablet, injection, etc.)? I'm not a peptide expert, but I can tell you the general approach I've used for assay specification setting.

Assuming this is a drug substance, assay specifications are generally set based on both analytical uncertainty AND the expected purity of the substance. In your case, if the drug is degrading over time, that would need to be factored into your assay limits. Assuming that the degradation products remain below your acceptance limits, it's generally acceptable practice to have assay limits which account for the maximum acceptable degradation over the shelf life of the API. You'll often see this reflected as an 'asymmetrical' limit (eg, 96.0 - 102.0%).

Obviously, the ideal situation here would be to minimize degradation through a change in the storage configuration/conditions; however, if that's not possible, wider limits can be justified, provided you know what degradation products are being generated, and you have safety information for those products.