Safety Concern Thresholds and Tox Assessment: SCT, TTC, PDE


Published on 05/12/2025

Safety Concern Thresholds and Tox Assessment: SCT, TTC, PDE

In the pharmaceutical industry, the safety and efficacy of drug products are of paramount importance. This tutorial provides comprehensive guidance on the assessment of safety concern thresholds related to extractables and leachables (E&L) as well as the pertinent concepts of analytical evaluation threshold (AET), dose-based threshold (DBT), and container closure integrity (CCI). These elements are crucial for ensuring that pharmaceutical products meet the strict compliance standards established by regulatory bodies such as the US FDA and EU GMP guidelines.

Understanding Extractables and Leachables (E&L)

Extractables and leachables are compounds that can migrate from packaging or other system components into pharmaceutical products. Understanding their behavior is essential to ensure patient safety, particularly with regards to biopharmaceuticals and single-use systems. A thorough E&L risk assessment is critical, especially in light of ongoing regulatory scrutiny following the implementation of FDA process validation guidelines.

The major steps in E&L analysis include:

  • Identifying Potential E&L Sources: Recognizing materials in contact with the drug product such as containers, closures, filters, and tubing.
  • Conducting Extractables Studies: Performing controlled extraction studies using solvents that mimic the drug product or its environment to generate a comprehensive list of extractables.
  • Performing Leachables Studies: Analyzing samples of the final drug product to identify any leachables that may have migrated during storage.

It is important to define appropriate limits for E&L substances, which typically involves understanding the toxicological profiles of the substances identified. Key regulatory guidelines to reference include the PQRI guideline for E&L and the relevant sections of EU GMP Annex 1. Risk assessments should align with these guidelines to ensure safety and compliance.

Safety Concern Thresholds: SCT and TTC Concepts

The concepts of Safety Concern Threshold (SCT) and Threshold of Toxicological Concern (TTC) are vital for evaluating the safety of chemicals present in pharmaceutical packaging. These thresholds serve as benchmarks for determining the acceptability of potential leachables without extensive toxicological testing.

Threshold of Toxicological Concern (TTC) refers to a concentration level below which chemicals are considered to pose minimal toxicological risk. The TTC values vary depending on the type of exposure and the duration of that exposure, making it imperative for companies to classify leachables accordingly.

On the other hand, the Safety Concern Threshold (SCT) is a concentration level used to indicate potential concern regarding leachables. SCT values often depend on the type of leachable—such as known carcinogens or reproductive toxins—highlighting the need for judicious risk assessment based on available toxicological data.

The essential steps focusing on SCT and TTC assessments include:

  • Determination of the Chemical Nature: Analyzing and categorizing identified substances based on available toxicological information.
  • Application of TTC Values: Establishing if the identified leachables fall below the TTC, allowing for more straightforward risk management.
  • Integration into Risk Assessment Frameworks: Incorporating SCT and TTC into broader E&L risk assessment practices for robust, defensible safety evaluations.

Organizations must utilize a science-based approach to relate the SCT and TTC to the specifics of their product and its packaging. Regulatory submissions must document these assessments and emphasize alignment with EMA and FDA guidelines during reviews.

Analytical Evaluation Threshold (AET) and Dose-Based Threshold (DBT) Calculations

The Analytical Evaluation Threshold (AET) and Dose-Based Threshold (DBT) represent quantitative benchmarks in E&L assessment that assist manufacturers in making informed safety decisions.

Analytical Evaluation Threshold (AET)

The AET quantifies the maximum concentration of leachables that can be present in a drug product before a regulatory submission is required. As a rule of thumb, the AET is often calculated using a risk assessment approach, where the concentration that does not exceed the acceptable daily exposure (ADE) is taken into consideration. The AET is generally defined using an equation such as:

AET = (TTC × body weight) / (daily intake)

Implementing AET effectively involves:

  • Establishing Patient Exposure Levels: Researching potential patient dosing and frequency to understand exposure duration.
  • Documenting Toxicological Data: Gathering evidence on the toxicity of leachables and ensuring these fit into the framework of established TTCs.

Determining Dose-Based Threshold (DBT)

DBT calculations also follow a toxicological-based methodology, where manufacturers determine allowable levels for leachables based on the potential body burden after drug administration. The DBT assists in further fine-tuning acceptable limits for components that might not benefit from an established AET.

DBT = (No-Observed-Adverse-Effect Level (NOAEL)) / (safety factor × patient weight)

To implement DBT effectively, the following actions should be taken:

  • Utilizing Reliable Toxicological Data: Engaging in literature reviews to support DBT calculations with robust evidence.
  • Coordinating with Regulatory Standards: Ensuring that calculations meet the expectations set forth by bodies such as the EMA and FDA.

Container Closure Integrity (CCI) in Relation to E&L Assessment

Container Closure Integrity (CCI) is the measure of the ability of a packaging system to maintain a sterile barrier against contamination. Ensuring CCI is critical, particularly for parenteral drug products. The importance of understanding CCI’s role in E&L evaluations cannot be overstated; compromised integrity can lead to unintended leachables or extractables entering the pharmaceutical process or product.

Key considerations in CCI evaluations include:

  • Method Selection: Employing suitable techniques, such as helium leak testing and vacuum decay methods, to confirm the integrity of drug packaging.
  • Comparative Analysis: Reviewing CCI results pre- and post-E&L event studies to discern potential correlations.

To conform to CCI standards, manufacturers must adhere to USP CCI guidelines which set parameters for packaging performance. This includes validation practices that ensure consistent performance across production lots.

Single-Use Systems Validation: Best Practices

Single-use systems (SUS) have gained momentum in the pharmaceutical industry for biomanufacturing processes due to the advantages of flexibility and reduced cross-contamination risks. However, validating these systems for E&L presents unique challenges.

A rigorous validation process must be adhered to for single-use systems, which includes:

  • Pre-Qualification: Evaluating the supplier qualifications and material safety data sheets to gauge compatibility with intended use.
  • Performing E&L Studies: Conducting extractables studies using simulated manufacturing conditions to quantify potential leachables.
  • Verification of Sterility and Integrity: Ensuring that the functionality and sterility of the SUS remain intact post-processing.

Each of these elements must be documented and included in the validation report, ensuring alignment with regulatory expectations such as those prepared by the PIC/S. These reports will often serve as essential elements in product dossiers for regulatory submissions.

Conclusion

In conclusion, the assessment of extractables and leachables, including the careful evaluation of safety concern thresholds, analytical evaluation thresholds, and the integrity of container closure systems, is essential in the pharmaceutical validation process. By adhering to established practices and guidelines, pharmaceutical professionals can ensure compliance and bolster patient safety. The integration of AET, DBT, and CCI evaluations into routine quality assessments provides a robust framework for mitigating risks associated with E&L in drug products. With the ever-evolving landscape of regulatory expectations, ongoing education and awareness of best practices are crucial in maintaining a competitive edge in pharmaceutical development and manufacturing.