Assay limit in the BP monograph

In the BP’s monograph we can see difference for assay limits. For some product the limit is 95-105% (narrow) but for some it is 90-115% (Broad) in the monograph. What would be reason behind this difference. e.g. for Clotrimazole Cream assay limit is 95% to 105%, where as for Tretinoin Gel the assay limit is 90 to 120%. Does this broader limit for Tretinoin Gel like product hints for addition of overages for instability of the formulation during manufacturing.

More likely the assay limits or API specifications are determined in clinical studies by the originator. Thus, you MUST comply with those limits when you are making these generics/OTC creams as evidenced in your ‘Bioavailability and Bioequivalence Studies’.

Thank you, I meant what else are considered for setting the specification limit for Assay by originator or the BP.

It is the originator who writes the assay specification for the pharmacopieas. For the raw material (drug substance) they would include moisture (to calculate the assay on the dry basis) and organic impurities (related substances for the drug substance only).