Stability Indicating Methods

The answer to the following reader question about stability indicating methods was supplied by LCGC’s “ Validation Viewpoint ” columnist Michael Swartz.

Q: If an assay method is by UV or titration for release testing, what should be used for shelf-life or stability testing? Can we use the same UV or titration method for a stability study or for shelf life specification for the determination of an assay test? If the related substance test is by HPLC for release testing, should we develop another stability indicating method or can we use the same test method given in the pharmacopoeia? Also, can we use same related-substance HPLC method for the assay test? Is it a requirement to have an HPLC method for a stability study or shelf-life specification? Are non-HPLC methods acceptable?

Michael Swartz: In my opinion, a stability indicating method can be any analytical method capable of measuring a loss of API upon storage. In other words, whatever method is used, it must be able to discriminate between the API and any degradants/impurities/excipients, and measure the potential loss upon degradation. In early studies, or in forced degradation studies, it might also be desired to measure the degradants as well.

Many methods these days are developed as combination methods, one method for related substances and assay. It puts a little more demand on the method from a validation standpoint (for example, it must perform over a wide range), but is acceptable. My preference however is to have separate methods, validated for their intended purpose.

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