Impurities

Substances in a drug substance or product other than the intended active ingredient and excipients. Related substances are product-related impurities, such as degradation products and synthesis by-products that resemble the active ingredient; impurities more broadly include process-related impurities, elemental impurities and residual solvents. Japanese specifications usually include a related substances test (類縁物質試験) with limits for individual and total impurities, following ICH Q3A and Q3B for small molecules and ICH Q6B for biologics. Reporting, identification and qualification thresholds decide which peaks must be named and justified.