Hi chunduri.2009,
From ICH Q3B(R2),
http://www.ich.org/fileadmin/Public_Web ... deline.pdfDegradation Product: An impurity resulting from a chemical change in the drug
substance brought about during manufacture and/or storage of the new drug product by the effect of, for example, light, temperature, pH, water, or by reaction with an excipient and/or the immediate container closure system.
Identified Degradation Product: A degradation product for which a structural
characterization has been achieved.
Unidentified Degradation Product: A degradation product for which a structural
characterization has not been achieved and that is defined solely by qualitative
analytical properties (e.g., chromatographic retention time).
Identification Threshold: A limit above (>) which a degradation product should be identified.
Qualification: The process of acquiring and evaluating data that establishes the
biological safety of an individual degradation product or a given degradation profile at the level(s) specified.
Qualification Threshold: A limit above (>) which a degradation product should be qualified.
Reporting Threshold: A limit above (>) which a degradation product should be
reported.
Appendix 1 of Q3B(R2) contains a plot which may help with explaining these definitions and their relationship.
A caveat can be the toxicity of the degradation product under consideration (upon its qualification).
Please, do you have further specific questions?