Impurity leachables screening tests are systematic analytical studies that detect, identify, and quantify substances migrating from product-contact materials—such as pharmaceutical packaging, medical devices, and single-use process systems—into drug products, biologics, or patient-contact fluids. Performed by accredited third-party laboratories in accordance with USP 1663, USP 1664, ICH Q3E, and ISO 10993-18, these screening studies are a critical component of patient safety assessment and regulatory submission strategy for pharmaceuticals, medical devices, and combination products.
Technical Overview
Leachables are organic and inorganic substances that migrate from product-contact materials into a drug product or biological fluid under normal conditions of storage, handling, and use. They originate from additives, processing aids, degradation products, and residual monomers present in elastomers, plastics, glass, coatings, adhesives, and inks. Extractables, by contrast, are compounds released from the same materials under exaggerated laboratory conditions such as aggressive solvents, elevated temperature, and extended contact time. An impurity leachables screening test is therefore a discovery-oriented analytical program that establishes the profile of potential and actual migrating impurities and evaluates them against scientifically justified safety thresholds.
Screening studies follow a risk-based, orthogonal strategy combining multiple chromatographic and spectrometric techniques, because no single analytical method can detect the full range of possible migrants. Results are interpreted against the Analytical Evaluation Threshold (AET), which is derived from the Safety Concern Threshold (SCT) conventionally set at 1.5 micrograms per day of patient exposure. Compounds detected above the AET are identified, semi-quantified, and routed for toxicological evaluation, typically in alignment with USP 1663 for extractables, USP 1664 and 1664.1 for leachables, the draft ICH Q3E guideline, ISO 10993-17 for toxicological risk assessment, and ISO 10993-18 for chemical characterization of medical devices.
Testing Samples
Pharmaceutical Packaging and Closure Systems
Elastomeric closures (vial stoppers, prefilled syringe plungers, cartridge seals), plastic bottles, films, laminates, blister foils, glass vials, label adhesives, and printing inks are screened for migrants that may partition into the drug product over its shelf life.
Medical Devices and Drug-Device Combination Products
Catheters, infusion sets, syringes, intravenous bags, extension tubing, inhalation devices, dialyzers, implants, and wound dressings undergo chemical characterization as part of the biological evaluation required by ISO 10993-1 and ISO 10993-18.
Single-Use Bioprocess Contact Materials
Membrane filters, process tubing, bioreactor bags, connectors, gaskets, and seals used in upstream and downstream bioprocessing are evaluated for migrants that could contaminate biologics or parenteral formulations.
Finished Product and Stability Samples
Drug product stored in its final container-closure system, including samples pulled at defined stability time points under ICH storage conditions, is analyzed to confirm which extractables actually become leachables at clinically relevant concentrations.
Testing Items
Typical scope of an impurity leachables screening program includes:
- Volatile organic compounds and residual solvents, such as styrene, acrylonitrile, vinyl chloride, and low-boiling aldehydes
- Semi-volatile organic leachables, including hindered phenol and phosphite antioxidants, plasticizers (phthalates, adipates, citrates), lubricants, slip agents, stearates, and siloxanes
- Non-volatile organic leachables, such as polymer oligomers, waxes, surfactants, and oligomeric degradation products
- Elemental impurities and heavy metals, including lead, cadmium, arsenic, mercury, nickel, chromium, zinc, tin, and catalyst residues, assessed in alignment with ICH Q3D
- Inorganic anions and cations, such as chloride, sulfate, nitrite, nitrate, and ammonium species
- High-concern compound classes, including nitrosamines, polycyclic aromatic hydrocarbons, primary aromatic amines, and monomers classified as mutagenic impurities
- Secondary degradants formed by reaction between packaging-derived extractables and the drug product matrix
Testing Methods
Extraction design is tailored to the intended use of the material. Exaggerated extractions employ model solvents of varying polarity (aqueous, acidic, basic, alcoholic, or hexane-based) at elevated temperatures with defined surface-area-to-volume ratios, in accordance with USP 1663 and ISO 10993-12. Accelerated and simulated-use extractions, including migration studies on finished product, are designed to reflect real clinical or storage exposure. The resulting extracts are subjected to orthogonal analysis:
- Headspace GC-MS for volatile organic compounds and residual monomers
- Direct-injection or derivatized GC-MS for semi-volatile organic compounds
- LC-MS/MS and LC-QTOF high-resolution mass spectrometry for non-volatile and thermally labile organics
- ICP-MS and ICP-OES for elemental impurities and heavy metals
- Ion chromatography for inorganic anions and small organic acids
- FTIR and NMR spectroscopy for structural confirmation of unknowns
- Gravimetric non-volatile residue (NVR) and total organic carbon (TOC) determination as complementary screening measures
Data treatment includes library-based and high-resolution mass spectral identification with assigned confidence levels (confirmed, probable, tentative, or unknown), semi-quantitation against structurally similar internal or external standards, and application of an analytical uncertainty factor—commonly 50 percent—when reporting against the AET, as recommended in USP 1663. Detected compounds exceeding the AET are prioritized for toxicological risk assessment under ISO 10993-17 or equivalent qualification frameworks.
Applications
Impurity leachables screening data support numerous regulatory and quality functions across the product lifecycle:
- Regulatory submissions, including IND, NDA, ANDA, BLA, and packaging component drug master files
- Chemical characterization reports supporting biological evaluation files for medical devices under ISO 10993-18
- Selection and qualification of container-closure systems and packaging suppliers
- Inclusion of leachables monitoring in drug product stability protocols
- Change control assessment when packaging materials, suppliers, or manufacturing processes are modified
- Extractables profile libraries that justify a reduced-scope or targeted leachables method for routine commercial batch release
- Support for biologics, biosimilars, generics, and drug-device combination products where container interaction risk is elevated
FAQ
What is the difference between extractables and leachables?
Extractables are compounds released from contact materials under exaggerated laboratory conditions such as strong solvents and elevated temperature, while leachables are the subset of those compounds that actually migrate into the drug product under normal storage and use conditions. Extractables studies define the candidate list; leachables studies confirm which candidates appear and at what levels.
What is the Analytical Evaluation Threshold (AET)?
The AET is a concentration limit derived from the Safety Concern Threshold, typically 1.5 micrograms per day, scaled by the patient's daily exposure to the drug product. Any leachable detected above the AET must be identified and toxicologically qualified. A screening uncertainty factor is generally applied so that method variability does not cause results near the threshold to be missed.
Which regulatory guidelines govern leachables screening?
Key frameworks include USP 1663 and 1664, the draft ICH Q3E guideline on extractables and leachables, ISO 10993-12 and 10993-18 for medical device chemical characterization, ISO 10993-17 for toxicological risk assessment, ICH Q3D for elemental impurities, and ICH M7 considerations for mutagenic impurities. Regional expectations from major regulatory agencies are generally aligned with these standards.
What extraction conditions are used in a screening study?
Extraction conditions are chosen based on material type, intended route of exposure, and product matrix. Typical designs include reflux, Soxhlet, sealed-vessel oven extraction at 40 to 70 degrees Celsius, autoclave or accelerated extraction, and simulated-use migration studies lasting from several days up to full product shelf life, with solvent pH and polarity matched to the drug product or clinical fluid.
How long does a typical screening study take?
A targeted extractables screening of a single material generally requires four to eight weeks including extraction, orthogonal instrumental analysis, data processing, and reporting. Full extractables-plus-leachables programs spanning multiple materials, simulated-use conditions, and stability time points may extend over several months and are best planned early in product development.
How are unknown compounds handled?
Unknowns detected above the AET are assigned identification confidence levels using high-resolution accurate-mass data, isotope patterns, and fragment spectra. Tentatively identified compounds are reported with semi-quantitative estimates against reference surrogates, and confirmation with authentic standards is recommended whenever the estimated exposure approaches or exceeds the qualification threshold.