Permitted Daily Exposure (PDE, also referred to as “permissible daily exposure”) is a health-based limit that defines the maximum acceptable daily intake of a substance without major risk to human health.
In the pharmaceutical industry, PDE is primarily applied to control impurities, residual solvents, elemental impurities, and cross-contamination arising from shared manufacturing facilities. Both the European Medicines Agency (EMA) and the International Council for Harmonisation (ICH) have incorporated the PDE concept into their quality guidelines, making it a cornerstone of modern risk-based pharmaceutical quality systems.
ICH and EMA frameworks: Regulatory Origins
PDE notion originates from toxicological risk assessment and is closely aligned with the Acceptable Daily Intake (ADI) used in food safety. EMA and ICH harmonized their approaches, particularly through ICH Q3C (Residual Solvents), ICH Q3D (Elemental Impurities), and the EMA guideline on setting health-based exposure limits for use in risk identification in the manufacture of different medicinal products in shared facilities.
Together, they create a coherent framework that links toxicology, manufacturing science, and regulatory compliance.
Scientific Basis for PDE Derivation
PDE is calculated using toxicological data, typically derived from non-clinical studies, and represents a substance-specific, health-based exposure limit.
The general formula for PDE includes the identification of a point of departure, such as the No Observed Adverse Effect Level (NOAEL) or Lowest Observed Adverse Effect Level (LOAEL), followed by the application of adjustment factors. These latter account for interspecies variability, human variability, duration of exposure, severity of toxicity, and data completeness.
Both EMA and ICH stress that PDE values must be scientifically justified, transparent, and reproducible. Human clinical data is preferred to be used, whenever it is available and relevant to the intended exposure scenario.
Application of PDE in Manufacturing and Quality Risk Management
One of the most significant applications of PDE within the EMA framework is in the assessment of cross-contamination risks in shared manufacturing facilities.
Rather than relying on default limits, such as parts per million or visual cleanliness, EMA expects manufacturers to establish health-based exposure limits derived from PDE values.
These PDE values then get translated into practical limits (for instance, the Maximum Allowable Carryover – MACO) defining cleaning validation acceptance criteria. This approach is fully aligned with ICH Q9 on Quality Risk Management, as it enables manufacturers to focus controls on substances that pose the greatest potential risk to patients.
ICH Q3C and Q3D Guidelines
ICH Q3C applies the PDE concept to residual solvents, categorizing solvents based on their toxicity and assigning PDE-based limits to ensure patient safety. Similarly, ICH Q3D establishes PDE values for elemental impurities, considering route of administration and duration of exposure.
In both guidelines, PDE serves as the scientific anchor that replaces historically fixed limits with substance- and exposure-specific thresholds. This evolution reflects a broader regulatory shift toward risk-based, science-driven decision making.
Regulatory Expectations and Documentation
Regulators expect PDE derivations to be thoroughly documented, including data sources, rationale for selected toxicological endpoints, and justification of adjustment factors. EMA inspections frequently assess the numerical PDE value, as well as the robustness of the underlying toxicological assessment, and its integration into the pharmaceutical quality system.
The PDE assessment should be conducted by an experienced toxicologist, responsible for ensuring its scientific validity and regulatory accuracy.
To summarize, by establishing health-based exposure limits grounded in scientific evidence, PDE enables more effective control of impurities and cross-contamination while supporting flexible, risk-based manufacturing strategies.
As regulatory expectations continue to evolve, a thorough understanding and correct application of PDE remains essential for ensuring patient safety and maintaining regulatory compliance, contact us to stay compliant.
