Control of Elemental Impurities in Pharmaceutical Products

Elemental impurities in pharmaceutical products may arise from various sources, including manufacturing processes (e.g., metal catalysts), raw materials, excipients, water, and production equipment. As a result, these contaminants may be present in the finished product. Since heavy metals are inherently toxic and offer no therapeutic benefit, their levels must be strictly controlled to ensure that any associated risk remains proportionate to the clinical benefit of the medicinal product.

This article reviews traditional methods for heavy metal analysis and highlights recent advances in the control of elemental impurities. According to ICH guideline Q3D, elemental impurities are classified into four categories based on toxicity and route of administration. Class 1 elements are highly toxic and require mandatory evaluation for all routes. Class 2 elements are route-dependent toxicants. Class 3 elements have relatively low toxicity, with assessment depending on exposure route. Class 4 elements are considered low risk and are generally excluded from routine evaluation.

For over a century, the heavy metals limit test described in the European and United States Pharmacopoeias served as a standard reference. However, current regulations recommend modern, selective, and highly sensitive techniques such as ICP-MS and ICP-OES. These methods are described in USP chapters <232> and <233> and European Pharmacopoeia chapter 2.4.20.