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Assay testing
While Providing the SPF formulas for Assay testing, how are the ranges determined?
What is the general rule of thumb?
Thanks,
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5 Replies
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Need more details…
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Bob, for eg. If we use 15.5% ZnO in a formula using a dispersion which has a range of 40-45% Active. How would you determine a range for future multiple production batches? When there is no consistency within the active content in dispersion itself?
Thanks
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Ahhh…I understand.
The FDA requirement for an Active Ingredient assay qualification is +/- 10% of the active ingredient. So, if you are claiming 10% active, for example, the FDA range is 9.0 - 11.0% assayed active. What that means in practice is that any assay result of 8.9% or lower, or 10.1% or higher results in a failed batch that must be destroyed. (Yes, destroyed. If you are playing strictly by the rules, once an OTC drug batch is finished, the active ingredient levels cannot be changed or altered in any way).Knowing that the consequences for going out of spec are so severe, I would absolutely insist on a Certificate of Analysis from my dispersion vendor that gave the PRECISE amount of ZnO in each lot of dispersion, or I’d find another vendor. If I could, I would analyze the ZnO percent of each lot of dispersion myself, as well.I understand that dispersion suppliers don’t want to commit to a tight specification on their TDS or sales specs, because the exact ratio of powder to carrier is going to vary depending on the absorption characteristics of the lot of powder that is being dispersed. Further, the absorption characteristics of the powder depends more on the particle size and particle size distribution of the particles than on the chemistry, so it’s a much harder (and more expensive) variable to tightly control.The bad news is that this all boils down to the fact that you’ll have to adjust the amount of dispersion that you use in your formula each time you get a new lot of dispersion in-house. The good news is that it’s job security, after a fashion. -
Oh, and by the way - the FDA takes a very, very dim view of testing for specific results, i.e. running the same test multiple times until you get the results you want. This applies to assay results and micro results, as well as SPF panel results.
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Thanks Bob for great explanation. .yes, adjusting by multiple testing is exactly what I was trying to avoid. But sounds like its a common practice, especially with dispersions.
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