List of Excipients in Branded Drug RELEUKO

RELEUKO Excipient Strategy, Patent Position, and Commercial Opportunities

Last updated: August 7, 2026

RELEUKO, the U.S. brand for filgrastim-aafi, is a biosimilar granulocyte colony-stimulating factor to Amgen’s NEUPOGEN. Its commercial opportunity depends less on active-ingredient differentiation than on formulation reliability, prefilled-syringe economics, supply continuity, contracting, and regulatory interchangeability. The product uses a conventional, preservative-free liquid formulation with sorbitol, polysorbate 80, acetic acid, sodium hydroxide, and water for injection. Its core U.S. composition is difficult to differentiate through excipients because biosimilar approval requires a highly similar quality profile to the reference product.[1]

What is RELEUKO and how does it compete?

RELEUKO contains filgrastim-aafi, a recombinant methionyl human granulocyte colony-stimulating factor. Accord Healthcare markets the product in the United States, and Intas Pharmaceuticals manufactures it.[1]

Attribute	RELEUKO
Active ingredient	Filgrastim-aafi
Reference product	NEUPOGEN, filgrastim
FDA pathway	Section 351(k) biosimilar application
U.S. approval	March 2022
Dosage form	Preservative-free injectable solution
Strengths	300 mcg/0.5 mL and 480 mcg/0.8 mL prefilled syringes
Administration	Subcutaneous or intravenous, depending on indication
Core indications	Cancer chemotherapy-associated neutropenia, acute myeloid leukemia, myeloablative therapy, peripheral blood progenitor-cell mobilization, severe chronic neutropenia, and hematopoietic acute radiation syndrome
U.S. interchangeable designation	No interchangeable designation is identified in the current FDA product materials reviewed for this analysis
FDA reference product	NEUPOGEN

RELEUKO competes with NEUPOGEN, Zarxio, Nivestym, and Granix. The product is positioned as a lower-cost filgrastim alternative for oncology, transplant, hematology, and hospital use.

What excipients are in RELEUKO?

The RELEUKO formulation contains the following inactive ingredients:

Excipient	Primary formulation function
Sorbitol	Tonicity adjustment and protein-stabilizing environment
Polysorbate 80	Reduction of interfacial adsorption and aggregation
Glacial acetic acid	pH adjustment and buffering contribution
Sodium hydroxide	pH adjustment
Water for injection	Vehicle

The labeled product has an acidic formulation, with a target pH of approximately 4.0.[1] It is preservative-free. That design is consistent with single-dose prefilled syringes and reduces concerns about preservative-related tolerability or protein interaction.

Why sorbitol matters

Sorbitol supports osmolality and can reduce stress on the protein during storage and handling. In a filgrastim product, the excipient must preserve biological activity without creating excessive viscosity or injection discomfort. Sorbitol also avoids the need for a more complex amino-acid or polyol system that could increase formulation-development and analytical comparability burdens.

Why polysorbate 80 matters

Polysorbate 80 protects filgrastim against adsorption to container surfaces and agitation-induced degradation. The commercial risk is oxidative or hydrolytic degradation of the surfactant, with potential formation of subvisible particles or protein aggregates. Supplier qualification, peroxide control, compendial testing, and lot-to-lot consistency are therefore material parts of the excipient strategy.

Polysorbate 80 is widely used in biologics, which supports procurement and regulatory familiarity. It also limits differentiation because competing filgrastim products commonly use similar surfactant-based stabilization approaches.

Why the formulation is preservative-free

A preservative-free presentation is commercially suited to oncology and hospital channels, where single-use syringes are standard. It avoids the need to demonstrate preservative efficacy and reduces concerns over repeated-dose exposure. The tradeoff is that the product depends more heavily on container-closure integrity, aseptic processing, cold-chain control, and single-use handling.

What formulations are protected by RELEUKO’s intellectual property?

RELEUKO’s principal regulatory asset is its biosimilar approval, not a broad, differentiated excipient patent estate. The public product profile does not identify a proprietary excipient platform comparable to a long-acting G-CSF delivery system.

The likely intellectual-property value is concentrated in:

• Product-specific manufacturing controls.
• Cell-line and fermentation processes.
• Purification and impurity clearance.
• Protein concentration and aggregation controls.
• Aseptic filling and prefilled-syringe assembly.
• Container-closure integrity.
• Stability and transport protocols.
• Trade secrets covering process parameters and analytical methods.

A conventional sorbitol-polysorbate 80-acetate formulation is unlikely to support a strong composition-of-matter patent position by itself. Any enforceable protection would more likely involve a narrow combination claim, concentration range, stability profile, container system, or manufacturing process. Such claims would need to overcome substantial prior art in recombinant protein formulations.

Can excipients create a follow-on patent strategy?

Yes, but the value is limited unless the formulation solves a measurable commercial problem. Potential strategies include:

1. Polysorbate-reduced or polysorbate-free formulations.
   These could target oxidation, particle formation, or long-term stability. The challenge is maintaining protein integrity and comparability.

2. Room-temperature or extended-temperature stability.
   A formulation with validated excursion tolerance could reduce distribution losses and improve hospital inventory management.

3. High-concentration presentations.
   A smaller injection volume could improve patient convenience, but viscosity, aggregation, syringeability, and dose accuracy become central development issues.

4. Autoinjector or wearable delivery.
   Device integration could create a differentiated product, although the target population and dosing frequency may limit the return compared with long-acting pegfilgrastim.

5. Low-silicone or alternative container systems.
   A specialized syringe could reduce particles or protein adsorption, but the benefit must be clinically or operationally meaningful.

The strongest commercial formulation opportunity is likely an improved presentation rather than a minor excipient substitution.

How does RELEUKO compare with competing filgrastim products?

Product	Sponsor	Active ingredient	FDA status	Commercial positioning
NEUPOGEN	Amgen	Filgrastim	Reference biologic	Established brand and clinical history
Zarxio	Sandoz	Filgrastim-sndz	Biosimilar	Early U.S. biosimilar entrant with broad payer familiarity
Nivestym	Pfizer	Filgrastim-aafi	Biosimilar	Large commercial infrastructure and hospital contracting
RELEUKO	Accord/Intas	Filgrastim-aafi	Biosimilar	Price competition, oncology-channel access, supply diversification
Granix	Teva	Tbo-filgrastim	Biologic, not biosimilar to NEUPOGEN in the U.S.	Direct short-acting G-CSF competitor

RELEUKO shares the filgrastim-aafi suffix with Nivestym. That does not make the products interchangeable. Interchangeability is a product-specific FDA designation, and pharmacy substitution rules depend on state law and payer policy.

What is the FDA and Orange Book status of RELEUKO?

RELEUKO is regulated as a biologic under the Public Health Service Act and approved through the FDA’s biosimilar pathway. It is not an ordinary small-molecule drug listed in the Orange Book.

The relevant FDA resource is the Purple Book, which records licensed biological products, biosimilars, and interchangeable biosimilars.[2] The FDA approval allows RELEUKO to rely on the reference product’s established clinical safety and efficacy framework, subject to biosimilar-specific analytical, pharmacokinetic, pharmacodynamic, immunogenicity, and clinical data.

Because RELEUKO is a biosimilar, it does not receive a new 12-year reference-product exclusivity period. NEUPOGEN’s reference-product exclusivity has expired, allowing biosimilar competition.

When does RELEUKO lose exclusivity?

RELEUKO does not have the conventional patent and regulatory exclusivity profile of a new chemical entity. Its commercial protection is based primarily on:

• FDA approval.
• Manufacturing know-how.
• Supply reliability.
• Customer contracts.
• Payer placement.
• Potential device or formulation improvements.
• Brand recognition within hospital systems.

The reference product’s biologic exclusivity period expired before RELEUKO approval. RELEUKO therefore entered a market where biosimilar competitors already existed. Its exposure is commercial rather than a near-term loss of regulatory exclusivity.

What patent litigation and Paragraph IV risks affect RELEUKO?

Paragraph IV litigation is a Hatch-Waxman mechanism for small-molecule ANDAs. It does not govern a biosimilar application under Section 351(k). RELEUKO therefore does not face a conventional Paragraph IV certification against NEUPOGEN.

Biosimilar patent disputes use the Biologics Price Competition and Innovation Act patent-exchange framework, often called the patent dance, together with declaratory-judgment and infringement litigation under the Patent Act.[3] The most relevant risks for RELEUKO are:

• Manufacturing-process patents.
• Formulation patents.
• Device and syringe patents.
• Cell-line or production patents.
• Contractual or licensing restrictions.
• Patent disputes involving future line extensions.

The mature age of filgrastim reduces the likelihood that fundamental active-ingredient patents block U.S. commercialization. The more credible barriers concern manufacturing know-how, presentation, and supply-chain execution.

What manufacturing and IP barriers affect RELEUKO?

Filgrastim is a recombinant protein, so manufacturing quality is central to the commercial profile. Key barriers include:

Protein quality control

Critical quality attributes include:

• Primary amino-acid sequence.
• Methionine status.
• Higher-order structure.
• Aggregation.
• Subvisible particles.
• Host-cell proteins.
• Residual DNA.
• Endotoxin.
• Potency and receptor-binding activity.

A change in polysorbate supplier, sorbitol grade, container material, or filling process can affect stability and comparability. The formulation therefore creates a quality-system burden even when the excipients themselves are inexpensive.

Cold-chain dependence

RELEUKO labeling requires refrigerated storage and protection from freezing and light.[1] Excipient and container choices must support the labeled storage window and permitted temperature excursions. A product with superior excursion stability could generate value through lower wastage, especially in hospital pharmacies and specialty-distribution channels.

Prefilled-syringe execution

The prefilled syringe is commercially important. Device defects, siliconization, needle performance, break-loose force, and dose accuracy can affect procurement decisions. A reliable presentation may be more valuable than a nominally cheaper vial if it reduces preparation time and medication errors.

What commercial opportunities exist for RELEUKO?

Hospital and oncology contracting

The largest near-term opportunity is institutional purchasing. Hospitals and oncology networks often evaluate:

• Net acquisition cost.
• Availability during shortages.
• Wholesaler coverage.
• 300-mcg and 480-mcg dose availability.
• Syringe usability.
• Reimbursement and coding.
• Conversion support.
• Product discontinuation risk.

Accord can compete by offering predictable supply and contract terms rather than relying solely on list-price discounts.

Biosimilar substitution and payer access

RELEUKO can gain share where payers promote biosimilar use without requiring automatic pharmacy substitution. Health-system formularies may adopt multiple filgrastim products to preserve supply resilience, or they may consolidate volume with one preferred vendor.

An interchangeable designation would have strengthened automatic-substitution potential. Without that designation, commercial adoption depends more on prescriber, pharmacist, payer, and institutional policy.

Shortage and supply-diversification value

G-CSF demand is operationally sensitive. Manufacturing interruptions, raw-material constraints, or oncology-treatment volume can create supply pressure. A second-source strategy has measurable value for hospitals. Accord’s opportunity is to position RELEUKO as a reliable supply option for high-volume accounts.

International expansion

The same formulation can support regulatory filings in jurisdictions that accept biosimilar comparability packages, but naming, interchangeability, substitution, and device requirements vary. The commercial opportunity is strongest where:

• Filgrastim utilization is high.
• Biosimilar adoption is established.
• Tender procurement is common.
• Cold-chain infrastructure is mature.
• Hospital systems purchase through centralized contracts.

How strong is the RELEUKO patent estate?

RELEUKO’s patent strength is moderate to weak as a standalone composition estate and stronger as a manufacturing and commercial-execution asset.

Asset category	Likely strength	Commercial relevance
Filgrastim active ingredient	Low	Foundational patents are expired or no longer blocking
Basic sorbitol/polysorbate formulation	Low	Extensive prior art
Manufacturing process	Moderate	Difficult to replicate, often protected as know-how
Analytical methods	Moderate	Supports regulatory control more than exclusion
Prefilled syringe presentation	Low to moderate	May support device-specific protection
Improved stability formulation	Moderate to high if clinically useful	Could support lifecycle management
Supply and contracting capability	Commercial rather than patent strength	High near-term importance

The defensibility of RELEUKO is therefore based on cost, quality, capacity, regulatory execution, and customer retention.

What are the generic and biosimilar launch scenarios?

Base-case scenario

RELEUKO maintains a position as one of several U.S. short-acting filgrastim suppliers. Pricing remains under pressure, while hospitals value supply continuity and dual sourcing.

Upside scenario

RELEUKO wins contracts through aggressive net pricing, reliable inventory, and a differentiated device or temperature-excursion profile. Greater payer adoption expands use beyond selected accounts.

Downside scenario

Nivestym, Zarxio, Granix, and future entrants compress margins. Hospitals consolidate purchases, and the product becomes a low-margin tender item. Any manufacturing or supply interruption would weaken customer confidence.

What licensing deals affect RELEUKO?

RELEUKO’s commercial structure involves Accord Healthcare and Intas Pharmaceuticals. Public product information identifies Accord as the U.S. commercial entity and Intas as the manufacturer.[1] The available labeling does not establish a separate, publicly disclosed excipient-technology license that would create a major royalty burden or constrain formulation lifecycle management.

Any licensing analysis should focus on:

• Territory rights.
• Manufacturing and supply obligations.
• Transfer pricing.
• Pharmacovigilance responsibilities.
• Device ownership.
• Formulation-improvement rights.
• Termination and change-of-control provisions.

Key Takeaways

• RELEUKO is a filgrastim-aafi biosimilar to NEUPOGEN, marketed by Accord and manufactured by Intas.
• Its formulation uses sorbitol, polysorbate 80, acetic acid, sodium hydroxide, and water for injection.
• The preservative-free, prefilled-syringe format supports oncology and hospital use.
• Excipient differentiation is limited because biosimilar approval requires high similarity to the reference product.
• The strongest lifecycle opportunities involve improved stability, device integration, lower injection volume, or alternative surfactant systems.
• RELEUKO is governed by the Purple Book and biologics law, not ordinary Orange Book or Paragraph IV procedures.
• Manufacturing reliability, cold-chain performance, hospital contracting, and payer access are more important than a broad composition patent estate.
• The commercial market includes Zarxio, Nivestym, Granix, and NEUPOGEN.
• Interchangeability status materially affects substitution and should be evaluated separately from biosimilarity.
• RELEUKO’s principal risk is margin compression in a mature, multi-supplier G-CSF market.

FAQs

Does RELEUKO contain albumin?

No. The labeled RELEUKO formulation uses sorbitol and polysorbate 80 rather than human serum albumin as a stabilizing excipient.[1]

Is RELEUKO preservative-free?

Yes. RELEUKO is supplied as a preservative-free injectable solution in single-dose prefilled syringes.[1]

Can RELEUKO be automatically substituted for NEUPOGEN?

Biosimilarity alone does not establish automatic substitution. Substitution depends on FDA interchangeability status and applicable state pharmacy law.

Does RELEUKO have a unique excipient patent?

The public product information does not identify a commercially significant proprietary excipient patent covering the marketed formulation. Its defensibility is more closely tied to manufacturing, quality control, and supply execution.

Is RELEUKO a competitor to pegfilgrastim?

Yes, but it is a short-acting filgrastim product. Pegfilgrastim products generally offer less frequent dosing, while RELEUKO competes on flexibility, institutional protocols, and acquisition cost.

References

1. U.S. Food and Drug Administration. (2024). RELEUKO (filgrastim-aafi) injection, prescribing information.
2. U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products.
3. U.S. Food and Drug Administration. (2020). Biosimilar biological products: Questions and answers on the BPCI Act.