I have run into a tricky case and was hoping you could help me to figure out whether validation is needed and, if so, what parameters to investigate.
I have a validated HPLC assay method for my drug product (a nasal spray), and another method for dosage uniformity. The ONLY differences between both methods are:
Final Sample concentration:
- Assay: 20ug/mL
- Uniformity: 4ug/mL (1/5 relative)
- Assay: 20uL
- Uniformity: 100uL (5/1 relative)
As you can see, the mass injected into the chromathographic system is the same, which leads me to believe that validation results for the assay method can be used for the uniformity method, thus no further validation might be required.
I am, however, worried that the slight differences in peak shape that could occur (increased width, decreased height) might invalidate the assay results.
What do you think? Would it be right to consider the assay method validation is also valid for the uniformity method?
Thank you in advance for any help and/or insight you could offer me.
PD: I know the specified range for assay is 80-120%, and for uniformity is 70-130%; I have validated the assay method in the range 50-150%, so this is not a concern.