The container that holds a pharmaceutical product is not inert. Every rubber stopper, every glass vial coating, every plastic film in contact with a drug product is a potential source of chemical migration into the dose. In 2026, regulators expect a written, defensible evaluation of container closure system leachables for every parenteral, ophthalmic, inhalation, and increasingly for solid oral dosage form. This guide explains how to design the extractables-to-leachables programme that supports the CCS safety dossier, and how to set the Permitted Daily Exposure limits that anchor the risk conclusion.
Why container closure system leachables matter
The pharmaceutical industry has learned this lesson expensively. The epoetin pure-red-cell aplasia event of the early 2000s was traced to leachables from uncoated rubber stoppers interacting with a reformulated polysorbate. The 2012 sartan nitrosamine discoveries revisited how we evaluate container contribution. Every high-profile impurity event in the last twenty years has had a CCS component somewhere in the root cause. The FDA guidance on container closure systems has therefore grown steadily in scope and expectation.
Container closure system leachables evaluation is not about whether something migrates, it always does. It is about whether the migrant quantities, over the intended shelf life, under the intended storage conditions, stay below Tolerable Intake values for the patient population served.
Distinguishing extractables from leachables in CCS programmes
The extractables study characterises what can be released from the container components under exaggerated conditions. The leachables study measures what actually migrates into the drug product under real storage. Container closure system leachables evaluation proceeds from extractables (worst case) to leachables (real case), and the correlation between the two is what regulators scrutinise.
For parenteral products, a leachables study is essentially always required. For solid oral dosage forms in bottles, it may be deferrable based on extractables data and clinical context. For inhalation products, both extractables and leachables are mandatory because lung exposure amplifies even trace contamination.
Designing an extractables study for container closure system leachables
Solvent selection
At minimum, three solvents of different polarity: water, 50% ethanol or similar mid-polarity, and isopropanol or hexane for non-polar. For formulation-specific studies, a polarity-matched simulant or the actual placebo is preferred. PQRI’s Parenteral and Ophthalmic Drug Products guidance remains the reference for simulant selection.
Extraction conditions
Exaggerated extraction, typically 50°C for 24-72 hours, with multiple cycles to demonstrate exhaustion. The exaggeration relative to clinical storage should be justified quantitatively, not by rule of thumb.
Analytical coverage
GC-MS for volatile and semi-volatile organics; LC-MS (both positive and negative ESI) for polar and non-volatile organics; ICP-MS for metals; IC for counterions. Every orthogonal technique is expected; a single-technique programme will be challenged.
AET and identification
The Analytical Evaluation Threshold for a container closure system leachables programme is derived from the clinical dose, contact area, and the Dose-Based Threshold per ICH M7 principles. Any extractable above AET must be identified to at least Level 3 confidence per AAMI TIR 106 and entered into toxicological evaluation.
Deriving PDE for container closure system leachables
For known leachables, antioxidants like BHT, plasticisers like DEHP, metal stabilisers, published PDE values are typically available from regulatory sources or pharmacopoeias. For unidentified or novel leachables, a compound-specific derivation is required. The process follows ICH M7 and ICH Q3C conventions: identify a point of departure from toxicity data (NOAEL, BMDL, TD50), apply uncertainty factors for species, individual variability, duration, and severity, and arrive at the PDE.
When toxicological data are sparse, read-across from structurally related substances is allowed. Our Read-Across Assessment method walks through the documentation expected by EMA and FDA reviewers. For routine PDE derivations on the most common rubber, glass, and plastic migrants, our Toxicology Monographs provide verified values with derivation histories.
Correlating extractables to leachables
A good container closure system leachables programme does not stop at the extractables inventory. It uses the extractables list to design a targeted leachables analytical method, typically LC-MS/MS at ng/mL sensitivity. Stability time points, 3, 6, 12, 24, and 36 months, are assayed to build a time-dependent migration profile.
The extractables-to-leachables correlation is the most-scrutinised part of the dossier. A leachable that appears without an extractables precursor is a red flag. A major extractable that does not leach is not a reassurance by itself; it must be explained.
Special cases in container closure system leachables
Biologics and protein drugs
Silicone oil from prefilled syringes, tungsten from pin-finishing operations, and leachables from uncoated rubber can all interact with proteins. Container closure system leachables evaluation for biologics extends beyond tox: immunogenicity and aggregation data may also be needed.
Prefilled syringes and autoinjectors
Needle-shield rubber, syringe barrel polymer, and the plunger stopper all contribute. Storage orientation and temperature variability across the cold chain complicate the leachables picture. Worst-case scenarios drive the study design.
Inhalation products
MDI canisters, valve elastomers, and DPI blister films are all potential leachable sources. Lung exposure amplifies toxicological concern; EMA and FDA expectations for inhalation CCS data are the tightest in the industry.
Combination products and device constituents
A drug-device combination product brings ISO 10993-18 principles into contact with ICH CCS expectations. Our E&L study design guide covers the medical-device-side methodology; for combination products, both frameworks apply.
Common deficiencies in CCS dossiers
Deficiency 1: Mismatched simulants. Using placebo when formulation effects are relevant (or vice versa) can invalidate the correlation to the product.
Deficiency 2: Incomplete identification. Unknowns above AET left unresolved force a conservative Cramer Class III treatment that often pushes the margin of safety below regulatory acceptance.
Deficiency 3: No stability-time migration curve. A single time-point leachables snapshot cannot support a shelf-life claim; regulators expect a time-dependent profile.
Deficiency 4: Weak PDE justification. Borrowing a PDE from an unrelated product line without reconciling the derivation rarely survives review.
Deficiency 5: Ignoring manufacturing variability. A container closure system leachables dossier based on a single lot of rubber stoppers ignores batch variability that can materially change the leachables profile.
How ToxLibrary supports your CCS programme
Container closure system leachables evaluation is high-stakes, technically complex, and increasingly expected at every stage from development through post-approval change. Our toxicologists build PDE derivations, interpret extractables-to-leachables correlations, and write the risk narratives that anchor the CCS safety dossier. If your team is scoping a new CCS study, managing a legacy migration question, or responding to a deficiency letter, reach out, a defensible CCS file is the foundation of product integrity.
