Process Related Impurities

Process related impurities are unwanted chemical or biological substances introduced during the manufacturing and purification of a biopharmaceutical product. They do not form part of the intended drug substance itself. Under ICH Q6B guidelines, they are divided into three categories: cell substrate-derived impurities (such as host cell proteins and host cell DNA), cell culture-derived impurities (such as antibiotics, inducers and serum), and downstream-derived impurities (such as solvents, enzymes, reducing agents and nitrosamines).

Process related impurities originate from the manufacturing process itself — from raw materials, cell culture components, or downstream processing reagents. Product related impurities, by contrast, are variants of the intended drug substance, such as aggregates, truncated forms, or incorrectly folded species. Both categories must be monitored and controlled as part of ICH Q6B compliance, but they require different analytical approaches.

ICH Q6B defines three categories of process related impurities: cell substrate-derived impurities, which include host cell proteins (HCP) and host cell DNA; cell culture-derived impurities, which include nutrient media components, antibiotics and inducers used during fermentation; and downstream-derived impurities, which include processing reagents such as enzymes, reducing agents, solvents, surfactants and nitrosamines introduced during purification.

Even at trace levels, process related impurities can pose significant safety risks. Some, such as nitrosamines, are potentially carcinogenic. Others, such as host cell proteins, can trigger immune responses in patients or may be deleterious to the actual drug product. Regulatory authorities including the FDA and EMA require manufacturers to demonstrate that downstream purification processes effectively reduce or remove these impurities, and that levels in the final drug substance and drug product remain at or below permitted thresholds.

The choice of analytical method depends on the chemical nature of the impurity. Commonly used techniques include LC-MS/MS or LC-MRM for antibiotics, reducing agents and nitrosamines; GC-MS for solvents, sugars and certain stabilisers; and HPLC-ELSD for surfactants and PEG-containing species. BioPharmaSpec's methods are specifically developed for each impurity and qualified to detect and quantify these impurities down to low ppm and ppb limits, in process intermediates, drug substance and drug product.

Nitrosamines are a class of chemical impurities that can form during the manufacturing or purification of pharmaceutical and biopharmaceutical products, often from raw materials or solvents. Many nitrosamines are classified as probable human carcinogens. Regulatory agencies including the FDA and EMA have introduced strict guidelines requiring manufacturers to assess, control and where necessary test for nitrosamine impurities in both drug substances and drug products.

Permitted levels vary by impurity type and are governed by product-specific regulatory guidelines as well as general ICH guidance. For many process residuals, limits are set in the low ppm or ppb range. The downstream purification process must be designed and validated to consistently reduce impurities to at or below these thresholds, with analytical testing of process intermediates and the final product used to demonstrate clearance.

Yes. Alongside a comprehensive suite of established methods for common process residuals, BioPharmaSpec's scientists can develop and qualify bespoke analytical methods for novel or process-specific impurities not covered by standard approaches. This includes developing pre-analysis purification steps to reduce matrix interference where required.