Many teams overestimate the reliability of packaging compatibility testing without phase-appropriate pharmaceutical excipient compatibility studies

Why Teams Overestimate Packaging Compatibility Testing Results

Packaging compatibility testing is a routine step in the development of pharmaceutical products, intended to ensure that the selected primary packaging—be it tubes, bottles, vials, or syringes—does not adversely interact with the drug product. Many pharmaceutical teams, however, place undue confidence in the conclusions drawn from these tests alone, particularly in early development phases. The assumption is often that if a drug formulation appears physically and chemically stable in a selected container-closure system, then the packaging is “compatible” for the intended shelf life and clinical use. Yet, this overlooks a critical component: the excipients within the formulation and their unique interactions both with the drug substance and the packaging materials.

For topical and ophthalmic products, which frequently contain complex combinations of excipients, the risk is even more pronounced. Teams may incorrectly believe that a lack of visible leachables, extractables, or degradation products during limited packaging compatibility testing equates to comprehensive product safety and stability. In reality, these studies may not capture subtle but significant interactions that manifest over time or under accelerated conditions. Even minor excipient-related changes—such as shifts in pH, viscosity, or preservative efficacy—can have major consequences for product performance and patient safety.

Overestimating the reliability of packaging compatibility testing, especially when excipient compatibility has not been robustly evaluated, can lead to downstream surprises during scale-up, stability, or regulatory submission. This is especially relevant for teams under pressure to accelerate timelines or minimize upfront costs. Proactive, phase-appropriate compatibility assessments that include both packaging and excipient interactions are essential to reduce risk and avoid costly reformulations or delays.

For further reading, see Plastics compatibility testing for packaging and IBCs from iso.org.

Role of Excipient Compatibility in Pharmaceutical Packaging Assessment

Excipients are more than just inert fillers in pharmaceutical formulations—they can significantly influence both the chemical and physical stability of drug products. In topical and ophthalmic drug development, excipients such as surfactants, preservatives, viscosity modifiers, and pH adjusters are essential for efficacy and user acceptability. However, their compatibility with both the active pharmaceutical ingredient (API) and the packaging system must be properly assessed.

Excipient compatibility studies are designed to identify potential interactions that could compromise product quality, safety, or efficacy. For example, certain excipients may:

• Extract plasticizers or stabilizers from packaging materials, leading to leachables in the final product
• Accelerate degradation of the API under specific storage conditions
• Interact with preservatives or antioxidants, reducing their effectiveness
• Alter physical properties such as viscosity or homogeneity

Ignoring excipient compatibility can obscure subtle but critical stability issues that only become apparent after extended storage or under stress conditions. Regulatory agencies are increasingly attentive to these risks, expecting clear evidence that excipient-package-drug interactions have been considered and managed. At Dow Development Labs, we routinely incorporate excipient compatibility assessments in our development programs for topical and ophthalmic products, helping clients anticipate and mitigate potential formulation challenges early in the process.

Limitations of Relying Solely on Packaging Compatibility Testing

While packaging compatibility testing is a fundamental component of pharmaceutical development, relying exclusively on it without considering excipient compatibility introduces several significant limitations. The most common challenges include:

• Narrow focus on container-closure interactions: Traditional packaging compatibility studies typically evaluate extractables, leachables, and visible changes. They may not detect API or excipient degradation unless specifically included in the analytical scope.
• Overlooking excipient-driven changes: Many excipients can catalyze degradation, precipitate, or alter the microenvironment within the package, leading to issues like API instability or reduced preservative efficacy that are not revealed by packaging tests alone.
• Limited simulation of real-world conditions: Standard tests may not account for all environmental factors (e.g., light, humidity, agitation) or the full range of patient use scenarios, potentially missing stress-induced incompatibilities.
• Inadequate detection of low-level interactions: Subtle changes in pH, viscosity, or appearance may be missed unless specifically targeted in the testing protocol.
• Risk of late-stage surprises: Issues not identified early may surface during scale-up, commercial stability studies, or regulatory review, resulting in rework, delayed timelines, or additional costs.

Comprehensive risk assessment demands a broader approach that integrates both packaging and excipient compatibility data, tailored to the specific needs and phase of the development program.

Phase-Appropriate Excipient Compatibility Studies: What They Add

Excipient compatibility studies should not be a one-size-fits-all exercise. Their design and scope must adapt to the stage of development—whether it’s preclinical, clinical, or commercial. At each phase, these studies provide critical insights beyond what packaging compatibility testing alone can reveal.

For example, in early development, excipient compatibility studies often focus on gross physical and chemical changes (e.g., precipitation, color change, pH drift) under accelerated conditions. This helps rapidly screen formulations for obvious incompatibilities. As programs advance, testing becomes more nuanced, incorporating:

• More sensitive analytical techniques to detect low-level degradation products or leachables
• Longer-term and real-time stability studies to evaluate changes over the proposed shelf life
• Specific monitoring of preservative efficacy, viscosity, and product homogeneity—key for topical and ophthalmic dosage forms
• Evaluation of excipient-API interactions that may be affected by the packaging environment (e.g., oxygen or moisture permeability)

Such phase-appropriate studies enable teams to catch incompatibilities early, optimize formulations, and build a robust data package for regulatory submissions. They also help avoid costly reformulation or repackaging late in development. Dow Development Labs incorporates phase-appropriate excipient compatibility assessments into our topical and ophthalmic development services, helping clients de-risk their programs from the outset.

Real-World Implications: Case Scenarios Where Gaps Occur

The risks of overestimating packaging compatibility testing become clear when examining real-world development scenarios. Consider the following illustrative examples:

• Preservative loss in ophthalmic solutions: A team develops a multi-dose ophthalmic product using a plastic bottle and standard packaging compatibility tests. Later, long-term stability testing reveals a gradual loss of preservative efficacy. Investigation shows that an excipient in the formulation is interacting with the bottle material, leading to preservative adsorption and diminished antimicrobial protection—an issue not identified in initial packaging compatibility testing.
• API degradation from excipient-induced pH changes: A topical gel formulation appears stable in a laminated tube during three months of accelerated packaging compatibility studies. However, on real-time storage, a slow pH drift caused by a buffering excipient results in increased API degradation and color change—only identified after extended excipient compatibility testing.
• Unanticipated leachables in clinical supply: In an effort to accelerate clinical supplies, a team skips comprehensive excipient compatibility evaluation, relying on packaging compatibility alone. During clinical use, trace leachables not detected in early testing are observed, traced back to a specific excipient extracting a minor packaging additive under storage conditions not fully simulated in initial studies.

Each of these cases underscores the importance of integrating excipient compatibility assessments with packaging studies to prevent late-stage surprises, regulatory questions, and costly program delays.

Integrating Packaging Compatibility Testing with Excipient Studies for Robust Results

To build a reliable, risk-mitigated development program, teams should integrate packaging compatibility testing with targeted excipient compatibility studies. This combined approach offers several practical benefits:

• Comprehensive risk identification: By evaluating both packaging and excipient interactions, teams can uncover a broader range of potential incompatibilities before they impact product quality or patient safety.
• Optimized formulation and packaging selection: Integrated studies help inform selection of both excipients and packaging materials that are best suited for the intended storage, distribution, and use conditions.
• Data-driven decision making: Robust compatibility data supports informed go/no-go decisions, regulatory filings, and responses to health authority queries.
• Reduced likelihood of late-stage reformulation or repackaging: Early identification of issues minimizes costly changes late in development.
• Alignment with regulatory expectations: Integrated studies demonstrate a proactive, science-driven approach to risk management, aligning with regulatory guidelines and reviewer expectations.

Dow Development Labs routinely designs and executes integrated compatibility testing programs for topical and ophthalmic products, providing clear, phase-appropriate data packages that help clients navigate development and regulatory milestones with confidence.

Regulatory Expectations for Packaging and Excipient Compatibility Evidence

Regulatory agencies worldwide—such as the FDA and EMA—expect comprehensive evidence that pharmaceutical products are stable, safe, and suitable for their intended use throughout their shelf life. This includes not only packaging compatibility testing but also deliberate assessment of excipient compatibility, particularly when new excipients or packaging types are introduced, or when products are intended for sensitive routes like ophthalmic or topical administration.

Guidelines such as ICH Q1A (R2) (Stability Testing of New Drug Substances and Products) and ICH Q3C (Impurities: Guidelines for Residual Solvents) emphasize the need for stability and compatibility data that account for all formulation components and their interactions with packaging. Regulatory reviewers are increasingly vigilant for:

• Evidence that potential leachables or extractables have been identified and assessed for safety
• Data demonstrating the stability of all key formulation attributes (API, excipients, preservatives) in the proposed packaging
• Justification for the selection of primary packaging based on compatibility results specific to the formulation
• Documentation of any observed or mitigated incompatibilities, and the rationale for formulation or packaging changes

Insufficient compatibility data can delay regulatory review, trigger additional information requests, or necessitate repeat studies. By proactively integrating excipient and packaging compatibility evidence, teams can strengthen their submission packages and reduce risk of regulatory setbacks.

How Dow Development Labs Supports Comprehensive Compatibility Testing

Dow Development Labs, based in Petaluma, CA, is experienced in supporting topical and ophthalmic drug development programs from early formulation through clinical supply. Our teams understand that robust compatibility testing involves more than standard packaging studies—it requires a phase-appropriate, integrated approach tailored to each product’s unique composition and intended use.

Our services include:

• Design and execution of packaging compatibility testing for a wide range of primary container-closure systems
• Excipient compatibility assessments under both accelerated and real-time conditions
• Analytical method development and validation to detect subtle changes in key product attributes
• Stability studies that incorporate both excipient and packaging variables, supporting regulatory requirements
• Data interpretation and reporting in formats aligned with current regulatory expectations

By partnering with Dow Development Labs, pharmaceutical teams can access the experience and resources needed to proactively identify and manage compatibility risks. Our integrated approach helps facilitate smoother development timelines and more robust regulatory submissions—reducing the likelihood of downstream surprises.

Ready to strengthen your compatibility testing strategy? Contact Dow Development Labs at 707-202-6965 to discuss how our integrated packaging and excipient compatibility services can support your topical or ophthalmic drug development program.