The sacred cow: the questionable role of assay methods in characterising the quality of bulk pharmaceuticals.

The specific and non-specific assay methods in the European and US Pharmacopoeias are critically evaluated. Emphasis is made on the discussion of the increasing role of impurity tests and decreasing, moreover questionable role of assay methods in characterising the quality of bulk drug materials. Various possibilities are also discussed for calculating the active ingredient content from the results of the assay and impurity tests. Only bulk drug materials are dealt with excluding from this study pharmaceutical formulations.