Common nitrosamine impurity limit calculation when it is contributing from both API as well as excipients

When common nitrosamine like NDMA, NDEA, etc… in Finish product are contributing from API and excipients both, then in this case how to set the limit? In this case do we still need to calculate based on the maximum daily dose of API only??
Do we need to calculate limit based on maximum total weight of formulation consumed daily?
What should be the calculation formula for calculating nitrosamine impurity in finish product in both the above cases?

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Just to confirm, when you say Nitrosamines from API and excipients that means for example:

Two different Nitrosamines, NDMA for API & “Nitroso-excipient” from excipient? In that case, the limit in ppm I think could will be still limited by the API as lets say MDD of the DP is 3 tablets, that would mean 3 times the excipient quantity as MDD of the “Nitroso-excipient” so AI (ng/day)/ MDD of “Nitroso-excipient”.

Or you mean same NDMA coming from both the API and excipient? In that case I would continue to take the API as the MDD.

I can be mistaken, but times ago, I asked myself the same question with azo-colorants for example as excipient.

@Diego_HM : I am talking about the same NDMA coming from both the API and excipient, in this case whatever the results of NDEA obtained in finish product is contributed by both API and excipient, then why we are calculating limit based on API only? should we not consider MDD of total weight of formulation while calculating the limit?

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