Practical Guide to Parenteral Drug Product Leachables: A Deep Dive into USP-NF 〈1664.2〉

This article provides a technical interpretation of USP 〈1664.2〉 for industry professionals seeking to understand the leachable assessment framework for intramuscular, intravenous, and subcutaneous drug products.

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1. Scope and Purpose of USP 〈1664.2〉: Building a Lifecycle Safety Framework for Parenteral Products

USP 〈1664.2〉 (Parenteral Drug Products — Intramuscular, Intravenous, and Subcutaneous) was published on May 1, 2025, with a public comment period closing July 31, 2025, and an anticipated official implementation date of August 1, 2026. This general chapter serves as an extension of USP 〈1664〉, working in concert with the following USP-NF chapters to establish a comprehensive, lifecycle-based leachable safety management system for parenteral products:

• USP 〈1663〉 — Assessment of Extractables from Plastic Packaging Components

USP 〈1665〉 — Characterization of Plastics Used in the Manufacturing of Biological Products

USP 〈665〉 — Plastic Components Used in the Manufacturing of Drug Products

USP 〈232〉 / 〈233〉 — Elemental Impurities in Pharmaceuticals

ICH Q12 — Technical and Regulatory Considerations for Pharmaceutical Product Lifecycle Management

📋 Framing for International Readers: USP 〈1664.2〉 represents the most comprehensive leachable assessment framework for parenteral products globally. Its multi-chapter architecture—spanning extractables, leachables, SUS components, elemental impurities, and lifecycle management—sets a new standard that regulatory authorities worldwide are increasingly referencing.

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2. Five Core Objectives of USP 〈1664.2〉: Fine-grained Risk Management, Dosage Form Adaptation, and Biological Product Safety

USP 〈1664.2〉 systematically refines leachable assessment requirements for parenteral products, with five core objectives:

Objective	Scope
Fine-grained Risk Management	Parenteral products enter the bloodstream or tissue directly, carrying inherently higher risk—assessment requirements are correspondingly more stringent
Dosage Form Adaptation	Differentiated testing strategies for SVP, LVP, PFS, and other dosage forms
Extended Leachables Sources	Production equipment, particularly single-use systems (SUS), is formally included in the assessment scope
Enhanced Biological Product Safety	New requirements address the interaction between leachables and biological product quality
Practical Solutions	Concrete strategies provided for low-AET scenarios in LVP and similar products

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3. AET Calculation by Dosage Form: LVP Products Face ppb-Level AET Thresholds Requiring Specialized Strategies

3.1 Core AET Calculation Logic

AET is inversely proportional to daily dose volume. Large-volume parenterals (LVP) with volumes such as 1,000 mL per bag can produce AET thresholds in the parts-per-billion (ppb) range—a level where standard analytical methods may struggle to achieve reliable quantification.

Summary of Core AET Formulas

Calculation Dimension	Formula	Applicable Scenario
Single-container AET	AET_container = SCT ÷ doses per day × labeled dose per container	Prefilled syringes (PFS), single-dose vials
Concentration-based AET	AET_conc = SCT ÷ doses per day ÷ daily dose volume	LVP bags, multi-dose containers
Component-level AET	AET_component = SCT ÷ doses per day × labeled dose ÷ number of components	Allocating leachable contributions from individual components
Uncertainty-adjusted AET	AET_adjusted = AET_initial ÷ UF (UF = 1/(1-RSD))	Quantification correction for unknown leachables

SCT (Safety Concern Threshold) is typically 1.5 µg/day, corresponding to approximately 50 ppb/day for a 30 kg body weight.

AET Calculation Examples by Dosage Form

Dosage Form	Key Parameters	AET Results	Key Assessment Requirements
Prefilled Syringe (PFS)	0.8 mL/unit, 1 unit/day	Container-level: 1.5 µg/unit; Concentration-level: 1.9 µg/mL	① Retain residual liquid/extraction samples; ② Characterize leachable contributions from plunger and barrel separately
Injection Pen	2 mL glass cartridge, 10 doses/day	Container-level: 15 µg/cartridge	Assess leachable accumulation over shelf life in multi-dose scenarios
Large-volume Bag (LVP)	1,000 mL/bag, 1 bag/day	Concentration-level: 0.0015 µg/mL (1.5 ppb)	① Use simulated study in lieu of direct leachable testing; ② Prioritize unknown leachable management at low AET
Multi-dose Vial	10 mL/vial, 1 dose/day	Container-level: 7.5 µg/vial; Concentration-level: 1.9 µg/mL	① Test leachable changes after multiple punctures; ② Monitor preservative-leachable interactions

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4. Low-AET Scenario Management: Three Strategic Pathways for Achieving Compliance

For LVP and similar products where AET falls below 1 ppb—below the reliable quantitation limits of standard analytical methods—USP 〈1664.2〉 provides three core strategic pathways:

Strategy	Core Rationale	Operational Requirements
Extractables Data Substitution	Extractables represent a “worst-case” scenario for leachables; qualifying extractables can exempt certain low-risk compounds from targeted leachable testing	Extraction conditions must simulate and modestly accelerate actual use conditions
Optimized Extraction Concentration Ratio	Increase the ratio of component mass to extraction solvent volume to elevate extractable concentrations to detectable levels	Calculate the number of components required per formula (e.g., 125 plungers needed to reach 100 mL extraction volume for a 0.8 mL dose)
Simulated Study Approach	Use simulated solvents that replicate the drug product’s “extraction capability” (pH, solvent type) while minimizing matrix interference	Simulated solvents must match the drug product’s extraction profile; results should complement, not replace, drug product testing

📋 For International Readers: The low-AET challenge is not unique to any single regulatory jurisdiction. Laboratories operating across US (FDA), EU (EMA), and Chinese (NMPA) markets all confront this analytical reality. The simulated study approach in particular has gained international regulatory acceptance as a scientifically justified alternative.

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5. Biological Product-Specific Requirements: Leachables Affect Protein Structure, Activity, and Immunogenicity

5.1 Impact of Leachables on Biological Product Quality

Leachable assessment for biological parenteral products must address not only direct toxicity, but also indirect impacts on protein structure and biological activity:

Impact Type	Manifestation	Typical Leachable Source
Protein Structural Degradation	Aggregation, deamidation, oxidation, and shear-variant formation	Tungsten (from syringe barrel forming process) and metal ions
Enhanced Immunogenicity	Altered protein conformation triggering immune responses	Elastomer vulcanizing agents and silicone oil
Reduced Bioactivity	Covalent binding of leachables to API	Aldehydes, ketones, and peroxides

⚠️ Key Distinction: Chemical drug parenterals require assessment of direct leachable toxicity only. Biological product parenterals must simultaneously assess direct toxicity AND indirect impacts on product quality—a requirement formally introduced in USP 〈1664.2〉.

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6. Production and Packaging Component Leachables Assessment

Component Type	Assessment Requirements	Reference Chapters
Container Closure System	All critical components require completed extractables studies	USP 〈1663〉, USP 〈1664〉
Production Equipment Components	SUS (Single-Use Systems) require chemical characterization per 〈665〉	USP 〈665〉, USP 〈1665〉
Post-Change Assessment	Material, supplier, or process changes trigger re-evaluation	ICH Q12

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7. Frequently Asked Questions

Q1: LVP AET is as low as 0.0015 µg/mL, but my detection method LOQ = 0.01 µg/mL. How do I achieve compliance?

Apply a three-tier progressive strategy:

1. Optimize extraction and detection methods: Increase component mass-to-solvent volume ratio; adopt high-sensitivity techniques such as LC-MS/MS (for organics) and ICP-MS (for elemental leachables)

Conduct simulated studies: Use simulated solvents matching the drug product’s extraction capability, minimizing matrix interference

Apply extractables data substitution: If toxicological evaluation of extractables confirms “no safety concern” (e.g., daily exposure below 30% of PDE), targeted testing of that compound in the drug product may be exempted

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Q2: What is the core difference between leachable assessment for biological products versus chemical drugs?

Biological product parenterals require simultaneous assessment of both direct leachable toxicity and indirect impacts on product quality—a requirement unique to the biological products framework.

Assessment Dimension	Chemical Drug Parenteral	Biological Product Parenteral
Primary Focus	Direct toxicity of leachables	Direct toxicity + impact on protein structure, activity, and immunogenicity
Testing Priorities	Targeted/nontargeted leachable quantification	Leachable quantification + protein stability monitoring (aggregation, purity, SEC-HPLC, MFI)
Assessment Framework	PQRI/ICH M7 threshold体系	USP 〈1664.2〉 + Product Quality Attribute (PQA) monitoring

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Q3: What is the core distinction between USP 〈1664.2〉 and USP 〈1664〉?

USP 〈1664〉 (Assessment of Drug Product Leachables) covers oral and topical dosage forms. USP 〈1664.2〉 is specifically designed for parenteral products, with key distinctions:

• More stringent AET requirements tailored to injection routes of administration

Formal inclusion of SUS (single-use systems) as a leachable source

Specific protein stability monitoring requirements for biological products

Concrete solutions for low-AET scenarios in LVP products

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Q4: How do I assess leachable accumulation over shelf life for multi-dose injectables (e.g., injection pens)?

Multi-dose injectables require a time-point sampling protocol under the USP 〈1664.2〉 framework:

• Establish sampling time points (e.g., Day 0, Day 90, Day 180)

Compare leachable concentrations at each time point against AET

Monitor preservative-leachable interactions (synergistic toxicity risks)

Assess protein stability changes (for biological products)

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Q5: When a component supplier changes, how should leachable assessment be handled?

Per USP 〈665〉 and ICH Q12 requirements, any material, supplier, or process change triggers re-evaluation:

1. Obtain extractables data for the post-change component

Compare extractables profiles between pre- and post-change components

Conduct toxicological evaluation of newly identified extractables

Conduct confirmatory leachable testing in the drug product when necessary

Update change control documentation under the ICH Q12 framework

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8. References

• [USP 〈1664.2〉 Parenteral Drug Products (Intramuscular, Intravenous, and Subcutaneous)](https://blog.brunslab.com/wp-content/uploads/2025/12/USP-NF-1664.2-513.pdf)

USP 〈1663〉 — Assessment of Extractables from Plastic Packaging Components

USP 〈1664〉 — Assessment of Drug Product Leachables

USP 〈1665〉 — Characterization of Plastics Used in the Manufacturing of Biological Products

USP 〈665〉 — Plastic Components Used in the Manufacturing of Drug Products

USP 〈232〉 / 〈233〉 — Elemental Impurities in Pharmaceuticals

ICH Q12 — Technical and Regulatory Considerations for Pharmaceutical Product Lifecycle Management

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Brunslab is a Chinese laboratory headquartered in Guangzhou, specializing in SUS and pharmaceutical packaging compatibility studies, extractables & leachables (E&L) research, risk assessment, impurities analysis, and medical device chemical characterization. This article is prepared for informational and technical exchange purposes. Contact: Tel: +86 20 31068557 | Email: contact@brunslab.com