FDA Review of Silicone Oil, Particles, and Container Compatibility for Biologics in Prefilled Syringes and Autoinjectors

How FDA evaluates silicone oil, subvisible particles, and drug-container compatibility for biologics in prefilled syringes and autoinjectors

When a therapeutic protein moves from a vial into a prefilled syringe (PFS), autoinjector, or pen, FDA does not treat the device as a separate mechanical question. BLA product quality reviews treat the primary container as part of the drug product. Silicone oil, tungsten, elastomer leachables, and the particles they generate are assessed as quality attributes that can affect stability, safety, and immunogenicity. This article summarizes how FDA reviewers have handled these issues across originator BLAs, 351(k) biosimilars, and post-approval supplements, and where those evaluations led to information requests or postmarketing commitments (PMCs).

Key takeaways

FDA's final guidance Immunogenicity Assessment for Therapeutic Protein Products gives the scientific basis that reviewers apply. Silicone-coated syringe components can promote protein denaturation and aggregation. Prefilled syringes are a particular concern because the product contacts several materials over time. Tungsten oxide leached from a syringe barrel has been reported to cause aggregation ⁶⁴⁶⁵⁶⁸⁶⁹.
Reviewers have required numerical subvisible particle specifications instead of report-only results. They have also asked for clinical immunogenicity data when a PFS showed materially higher particle counts than the vial presentation ¹³⁰¹³¹²⁵².
When particle or leachables characterization was incomplete at approval, FDA has often handled the gap through PMCs (Orencia, Pegasys, Lucentis, Kesimpta, Eylea, Boncresa) rather than by withholding approval ³³³⁴³⁹⁴¹⁴²⁴³¹³⁵¹³⁶.
Compatibility is expected for each container closure system with the final formulation. For biosimilars, this applies even when the reference product is supplied in a vial ⁷⁰²¹⁸.

The regulatory framework reviewers apply

The Immunogenicity Assessment for Therapeutic Protein Products guidance is the reference point that BLA quality reviews most often reflect. On silicone oil and container interactions, it states that silicone oil-coated syringe components can provide an environment in which proteins denature and aggregate. It identifies container-closure interactions as a particular concern for prefilled syringes because the product contacts multiple materials and surfaces over time. It also notes that glass and air interfaces can drive denaturation and aggregation ⁶⁴⁶⁵.

On subvisible particles, the guidance recommends assessing the range and levels of 2 to 10 µm particles initially and throughout shelf life. It asks sponsors to work toward characterizing 0.1 to 2 µm particles as methods become available. It flags the potential immunogenicity of 0.1 to 10 µm particulates and cautions that a single aggregate-measurement method is not sufficient ⁶⁶⁶⁷.

On leachables, the guidance explains that leachables may increase immunogenicity by modifying the protein or by acting directly as adjuvants. It cites tungsten oxide leached from a syringe barrel as an example of a leachable reported to cause aggregation. FDA recommends a comprehensive extractables and leachables (E&L) assessment and evaluation of leachables for each product in its storage container under real-time and stress conditions, with compatibility testing of their effect on product quality ⁶⁸⁶⁹.

For biosimilars, FDA's Questions and Answers on Biosimilar Development and the BPCI Act allows a proposed biosimilar to use a PFS even if the reference product is supplied in a vial. Biosimilarity and device performance requirements must still be met, and compatibility of the new container closure with the final formulation must be shown through studies such as E&L and stability testing ⁷⁰. FDA's advice to the Hadlima sponsor applied this directly. Each proposed PFS or autoinjector container closure system should be shown compatible with the final formulation, with E&L testing of every direct-contact part and stability testing in each system ²¹⁸.

Silicone oil

Silicone oil as a risk-ranked quality attribute

In the Nucala (mepolizumab) PFS review, FDA listed silicone oil as a safety and immunogenicity risk arising from the manufacturing process and the container closure system. The sponsor did not designate silicone oil as a critical quality attribute. The reviewer nonetheless found the risk assessment and control strategy adequate ¹⁷³³⁴⁸³⁴⁹. The Tezspire (tezepelumab-ekko) review describes silicone oil as a lubricant on the inside of the syringe barrel, the outside of the needle, and the plunger stopper of the accessorized PFS. The excerpts reviewed do not record a separate reviewer finding or limit on silicone oil ⁵²⁵³.

Formulation-dependent silicone sensitivity

The Orencia (abatacept) subcutaneous PFS supplement is an example of silicone sensitivity that depends on formulation. The review states that abatacept can form insoluble filamentous particles on contact with silicone unless it is appropriately formulated. For this reason the lyophilized presentation was used with an unsiliconized syringe ³⁰¹.

Silicone droplets compared with proteinaceous particles

The Simponi (golimumab) review shows how FDA handles uncertainty about whether particles in a PFS are silicone droplets or protein. FDA reported five- to tenfold more subvisible particles in the PFS than in the liquid-in-vial presentation. The sponsor attributed most of the increase to droplets. Reviewers remained concerned because droplets can associate with protein and the absence of protein in the particles could not be confirmed, even though the two presentations were comparable in other biochemical assays ¹³¹²⁵¹. The outcome is described under subvisible particles below.

Morphology-based methods appear in several reviews. In the Nucala review, HIAC light obscuration is described as counting subvisible particles without identifying their type, while micro-flow imaging (MFI) assesses morphology. Round particles were treated as possible silicone-oil droplets or air bubbles, and non-round particles as typically proteinaceous ²⁹⁹. In the Kanjinti (trastuzumab-anns) biosimilar review, MFI separated spherical particles (silicone oil) from non-spherical particles (protein) at 5 µm and above. The non-spherical fraction was treated as the more biologically relevant attribute for the similarity assessment ³⁰⁰.

Silicone oil under transport stress

For the Lucentis (ranibizumab) PFS, FDA identified a gap in shipping validation. The combined effects of vibration, pressure changes, and moderate temperature fluctuations on product quality had not been tested in the presence of silicone oil and tungsten in the syringe barrel. Simulation, stability, and shipping-container studies gave some assurance. FDA still obtained a PMC to ship product through representative commercial lanes and compare quality before and after shipment, including container closure integrity and subvisible particles ³⁹⁵⁰⁵¹³⁰²³⁰³.

Intravitreal presentations

Silicone oil carries specific clinical risks for intravitreal products. The use-related risk assessment for Yesafili (aflibercept-jbvf) listed injection of silicone oil as a potential cause of increased intraocular pressure, inflammation, floaters, eye pain, and vitreous detachment. It listed injection of foreign particulates as a potential cause of pain, intraocular inflammation, and increased intraocular pressure. These were potential harms in a risk analysis, not reported contamination findings ²⁶⁴. The Vabysmo (faricimab-svoa) PFS instructions require the supplied injection needle, which has an integrated filter, and prohibit use if particulates, cloudiness, or discoloration are visible ²⁶⁶²⁶⁷.

For Eylea (aflibercept), FDA issued PMCs after increased intraocular inflammation rates were linked to syringe lots. The sponsor was to summarize the syringe supplier's final investigation and leachables/extractables study and to run further studies using aflibercept drug product and the implicated syringe lots to look for a root cause ⁴¹⁴²²⁷⁴²⁷⁵. The reviewed excerpts state the required work but not the root cause ²⁷⁴.

Subvisible particles

Specifications instead of report-only results

In the Simponi review, FDA accepted report-only results for translucent and subvisible particles during clinical development. For the BLA, it required numerical specifications, citing the immunogenicity potential of particulate matter and aggregates in protein products. The reviewer stated that the sponsor's argument based on USP requirements did not resolve the concern ¹³⁰. Other approved PFS and autoinjector products include subvisible particles in release specifications. The Aimovig (erenumab-aooe) 70 mg/mL PFS specification lists light obscuration as the test method ¹³²¹³³. The Amjevita (adalimumab-atto) PFS release specification includes per-container subvisible particle limits, although the limits are redacted ¹³⁴.

Clinical data when PFS particle levels differ from the vial

Because the Simponi PFS contained substantially more subvisible particles than the vial and protein content in the particles could not be ruled out, FDA required clinical data showing that the PFS would not cause clinically meaningful differences in immunogenicity or safety. FDA said subgroup analyses of the ongoing Phase 3 trials, which used both presentations, could meet this requirement without a new trial ¹³¹²⁵². The safety and immunogenicity comparison was then analyzed using the Phase 3 data ²⁵³²⁵⁴.

Characterization gaps handled through PMCs

Orencia (abatacept) SC PFS: FDA recommended approval with a PMC to develop methods for characterizing micron and submicron particles in stressed or accelerated drug product, to assess whether the two size ranges correlate, and to propose a control strategy for product under approved storage conditions. A separate PMC required release acceptance criteria to be reevaluated using at least 30 commercial lots ¹³⁵¹³⁶¹³⁷.
Pegasys (peginterferon alfa-2a) PFS: PMCs required monitoring of subvisible particles in commercial PFS at release and under refrigerated and stressed or accelerated conditions. A further PMC required a feasibility study of analytical techniques for a specified (redacted) particle size range ³¹³².
Lucentis (ranibizumab) PFS: The commercial shipping PMC included subvisible particle testing before and after shipment ³⁹.

Gaps identified during review

The Udenyca (pegfilgrastim-cbqv) quality review identified missing data for 2 to 10 µm particles and requested updated PFS compatibility studies ¹³⁸. For Stelara (ustekinumab), translucent visible particles formed faster in PFS validation batches than in clinical batches stored under recommended conditions, and FDA asked for an investigation into the cause ³⁶. For Benlysta (belimumab), FDA commented on drug product testing in prefilled syringes. It noted that subvisible particles can form over time, can indicate stability changes, can affect product quality, and can increase immunogenicity ¹⁷⁴. The Tezspire and Enspryng (satralizumab) quality assessments also identified subvisible particles as a potential immunogenicity concern. The Enspryng review linked them to manufacturing and the container closure system ¹⁷⁵¹⁷⁶¹⁷⁷¹⁷⁸.

On orthogonal methods, FDA told the Inflectra (infliximab-dyyb) sponsor that testing ten additional lots of each compared product by MFI and HIAC light obscuration was generally adequate. FDA also said that further orthogonal testing might be needed after it reviewed the results ¹³⁹.

Tungsten and other syringe-derived impurities

FDA reviewers have asked direct questions about tungsten in prefilled syringes. In the denosumab review (Prolia/Xgeva), FDA asked whether the tungsten pins used to generate material for spiking studies had been exposed to conditions that could oxidize tungsten. FDA also requested any available measurements of tungsten in denosumab from the PFS, along with the spiking-study protocols and results ²⁷¹²⁷². In the Zinbryta (daclizumab) review, FDA stated that prefilled syringes can introduce tungsten and silicone, which may affect stability and immunogenicity. FDA called for impurity measurements, comparability testing, and spiking studies if new impurities were found ²⁷³.

The Pegasys PMCs show the same spiking-study approach applied to leachables. The sponsor was to identify and semiquantify specified (redacted) leachables in syringes from both suppliers and measure their levels in commercial batches. It was then to assess their effect on protein quality through a sensitivity/spiking study and assess a syringe control strategy ³¹³²³⁵⁰. The redacted text does not identify the leachable species ³⁵⁰.

Extractables, leachables, and drug-container compatibility

Risk-based E&L programs for PFS components

Recent BLA reviews describe staged E&L programs that cover every product-contact component:

Product	Components and approach	FDA follow-up
Fasenra (benralizumab)	Three stages: forced extraction, buffer simulation, then drug product leachables and elemental impurities. Covered the glass barrel/staked needle, plunger stopper, and elastomeric needle shield, using GC/MS, LC/MS, and ICP ⁹⁴	FDA requested a safety assessment; study reports were submitted in response to a later information request ⁹⁵
Nucala (mepolizumab)	Extraction of the plunger stopper and needle shield. Risk from the glass syringe and steel needle was judged low. 12-month leachables testing on three batches at two conditions ⁹⁶⁹⁷⁹⁸	FDA requested the full study reports. The extractables study was not used to set target leachables ⁹⁸⁹⁹¹⁰⁰
Exdensur (depemokimab-ulaa)	Headspace and solvent extraction of the stopper and needle shield, with selected extractables monitored as leachables. Glass and needle assessed for elemental leachables under accelerated conditions ⁷²	CMC team agreed that omitting harsh extraction of glass and needle was not a concern ⁷²
Yuflyma (adalimumab-aaty)	Extraction limited to the plunger stopper. Omission of glass extraction accepted because inorganic leachables testing was negative ¹⁰¹	No rationale given for omitting the needle/rigid shield, but not a concern because leachables were negative ¹⁰¹¹⁰²
Eticovo (etanercept-ykro)	Barrel/needle-shield assembly and stopper extracted separately, with screening for metals and organic classes ¹⁰³¹⁰⁴²⁴⁷²⁴⁸	FDA requested longer-term leachables data. Data through 36 months at 2 to 8°C were provided, including ICP/OES metals analysis ²²⁰
Idacio; Tyenne	Extraction of syringe barrel and stopper, with drug product (and buffer or placebo) leachables under long-term and stressed conditions ¹⁰⁵¹⁰⁶	None stated in reviewed excerpts ¹⁰⁵¹⁰⁶

Compatibility gaps that led to PMCs or requests

Orencia: Syringe and contact-equipment compatibility studies were missing, did not reflect manufacturing conditions, or did not report E&L, and metals data were absent. PMC #10 required extractables testing of drug-contacting PFS components under exaggerated conditions and leachables testing of assembled syringes across shelf life under real-time and accelerated conditions ³³³²⁵.
Kesimpta (ofatumumab): PMC to study leachables in commercially representative drug product stored in the intended PFS at 5±3°C through the proposed expiry ³⁴.
Enbrel (etanercept): FDA asked the sponsor to determine whether drug product could contact the natural-rubber needle shield and, if so, to propose solutions for quality, safety, or leachables concerns ³⁸.
Stelara: FDA asked for identification of a peak observed in placebo syringes stored at 25°C during leachables studies and an assessment of its effect on product quality ³⁵.
Nypozi (filgrastim-txid): FDA found the refrigerated and accelerated syringe leachables data insufficient to confirm compatibility through expiry and requested end-of-shelf-life data under long-term storage conditions ²⁵⁰.
Boncresa: PMC to conduct a leachables study of the primary container closure system ⁴³⁴⁴.

Stability as compatibility evidence

For many biosimilar PFS and autoinjector presentations, reviewers accepted real-time, accelerated, and stressed stability data in the final container as the main compatibility evidence. For Udenyca, PFS batches were monitored for potency, particulates, strength, and purity by RP-HPLC and SEC, along with container integrity and extractable volume, and no change attributable to container incompatibility was seen ²⁴⁴. The Hyrimoz (adalimumab-adaz) review reported 30 months of stability data for 14 PFS lots and 14 months for an autoinjector lot, and found the program adequate ²⁴⁵. For Hulio (adalimumab-fkjp), which uses a plastic PFS, compatibility and stability studies supported 36 months at 2 to 8°C ²⁴⁶. When Palynziq (pegvaliase-pqpz) moved from a vial to a glass PFS with a staked needle, comparability was based on lot release, long-term stability, container closure compatibility testing, and additional characterization ²⁴⁹.

Autoinjector and PFS functional performance with the biologic

Device verification in these reviews is expected to use the actual drug product. For Emgality (galcanezumab), FDA recommended verifying dose accuracy, activation force, needle extension, dispensing time, and break-loose/glide force using the to-be-marketed device with the intended biologic. Any surrogate fluid would need a scientific justification based on properties such as viscosity ²⁰⁵.

Nucala: Delivered volume, break-loose force, and glide force passed for the safety syringe assembled with the mepolizumab PFS ²⁰⁶²⁰⁷²⁰⁸²⁰⁹²¹⁰.
Amjevita: The PFS met break-loose extrusion-force and delivered-volume specifications across temperature and post-transport testing. The SureClick autoinjector maintained delivered volume and injection time across the same conditions ²¹¹²¹².
Hyrimoz: FDA asked for PFS release specifications that included both dose accuracy and break-loose/glide force ²¹³.
Entyvio (vedolizumab): FDA accepted autoinjector functional stability data through 18 months refrigerated, but found the PFS-plus-needle-safety-device response inadequate. It requested injection-force curves to detect possible clogging peaks ²¹⁴.
Semglee (insulin glargine) pen: ISO 11608-1 dose-accuracy criteria were met, testing with commercial needles passed, and E&L results supported compatibility of the glass cartridge and rubber closure system ²¹⁵²¹⁶²¹⁷.

Container closure integrity is also checked at the syringe level. FDA asked Xolair (omalizumab) to validate its dye-leak test using syringes with positive controls close to the validated detection limit ⁴⁰. FDA asked Stelara for the sensitivity of its syringe dye-ingress study ³⁷.

Practical implications for sponsors

Across these reviews, the same expectations recur:

Treat silicone oil as a risk-assessed attribute. It may not need to be designated a CQA, but the risk assessment and control strategy (process and container closure system) should be documented and should account for formulation-specific sensitivity, as in the Nucala and Orencia reviews ¹⁷³³⁰¹³⁴⁹.
Use orthogonal particle methods that can separate droplets from protein. Light obscuration alone does not identify particle type, so MFI or similar morphology-based methods are used to separate silicone droplets from proteinaceous particles ²⁹⁹³⁰⁰. If protein content cannot be excluded and PFS counts exceed the vial, expect requests for clinical immunogenicity bridging ¹³¹²⁵².
Set numerical subvisible particle specifications and plan for submicron characterization. In the Simponi review, report-only results were not accepted at the BLA stage, and submicron characterization has been a recurring PMC ¹³⁰¹³⁶.
Cover every product-contact component in E&L, with leachables data through expiry. This includes elastomeric needle shields and stoppers, and metals including tungsten. Omissions need a justification ⁶⁹¹⁰¹²⁵⁰³²⁵.
Test the combination under real-world stress. Shipping, temperature, and functional testing should use the actual biologic in the final presentation ³⁹²⁰⁵³⁰².

Readers who need product-specific detail, such as the exact PMC wording for a given BLA, how a sponsor's particle control strategy changed between submissions, or how intravitreal syringe reviews compare across aflibercept biosimilars, can ask Rhizome directly for a targeted follow-up.