Navigating Residual Solvent Regulation and Permitted Daily Exposure: Global Challenges and Harmonization

Introduction: Residual solvents, also called organic volatile impurities, are often used in pharmaceutical manufacturing. They may stay in drug substances, excipients, and finished products. Although these solvents have no therapeutic function, their potential toxicity can threaten patient safety and product quality. To manage these impurities, global regulatory agencies have set limits based on science. Methods: This article looks at the regulatory challenges of overseeing residual solvents under the International Council for Harmonisation (ICH) guidelines and major agencies like the Central Drugs Standard Control Organization (CDSCO), European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), and U.S. Food and Drug Administration (US FDA). Differences still exist in adoption timelines, pharmacopoeial methods, and the interpretation of permitted daily exposure (PDE) limits. Results: Scientific challenges involve determining PDEs for solvents that are not listed, filling in toxicological data gaps, extrapolating across different administration routes, and validating analytical techniques like gas chromatography. Historical and recent contamination events, such as diethylene glycol poisoning and methanol-tainted sanitizers, show the serious risks of inadequate solvent control. Discussion: Protecting public health requires clear, evidence-based PDE derivation, ongoing regulatory updates, and a coordinated global plan for managing residual solvent risks in pharmaceuticals. Conclusion: Residual solvents must be carefully regulated to ensure patient safety and consistent product quality. Differences among global agencies, scientific data gaps, and real-world contamination events highlight the need for harmonized, science-driven approaches to residual solvent control.