: While not a "paper," the USP 39–NF 34 PDF itself is the primary source. You can access historical USP compendia via the USP Reference Standards or USP Historical Library (subscription required, but many university libraries have access).
Some pharmaceutical products were approved based on USP 39 standards. Companies performing stability studies or retrospective analyses may need to refer to the exact standards that were official at the time of a drug’s approval. usp 39 pdf
: This edition and its supplements continued the industry-wide shift toward instrumental methods for testing heavy metals, aligning with international ICH Q3D guidelines. : While not a "paper," the USP 39–NF
limits for elements based on how a drug is taken (oral, parenteral, or inhaled). For example, inhaled drugs have much stricter limits for certain metals because they enter the bloodstream faster through the lungs. Official Recognition: For example, inhaled drugs have much stricter limits