List of Excipients in Branded Drug ONPATTRO

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Alnylam Pharmaceuticals Inc	ONPATTRO	patisiran	71336-1000	1,2-DIMYRISTOYL-SN-GLYCERO-3-CARBOXAMINOPROPYLPOLYETHYLENE GLYCOL 2000 METHYL ETHER	2029-04-15
Alnylam Pharmaceuticals Inc	ONPATTRO	patisiran	71336-1000	1,2-DISTEAROYL-SN-GLYCERO-3-PHOSPHOCHOLINE	2029-04-15
Alnylam Pharmaceuticals Inc	ONPATTRO	patisiran	71336-1000	CHOLESTEROL	2029-04-15

Onpattro Excipient Strategy and Commercial Opportunities

Last updated: August 11, 2026

Onpattro (patisiran lipid complex) uses a four-lipid nanoparticle system with DLin-MC3-DMA, DSPC, cholesterol, and PEG2000-C-DMG. The formulation is a commercial reference point for hepatic delivery of small interfering RNA (siRNA). Its excipient strategy creates opportunities in ionizable lipids, helper lipids, PEG-lipid alternatives, sterile manufacturing, lipid raw-material supply, and next-generation RNA delivery systems. The primary commercial constraint is that Onpattro’s clinical and regulatory value is moving toward newer Alnylam products, particularly Amvuttra (vutrisiran), which offers subcutaneous administration and less frequent dosing.

What excipients are used in Onpattro?

Onpattro is an intravenous lipid complex containing patisiran, a double-stranded siRNA, and four principal lipid components. The FDA prescribing information identifies the formulation as a lipid complex composed of DLin-MC3-DMA, DSPC, cholesterol, and PEG2000-C-DMG. The product is supplied as a 10 mg/5 mL concentrate, equivalent to 2 mg/mL of patisiran, for dilution before intravenous infusion.[1]

Component	Functional role	Commercial significance
Patisiran sodium	Active siRNA	Silences transthyretin messenger RNA
DLin-MC3-DMA	Ionizable cationic lipid	Enables RNA encapsulation and endosomal release
DSPC	Helper phospholipid	Supports bilayer structure and particle stability
Cholesterol	Structural lipid	Improves particle integrity and membrane interaction
PEG2000-C-DMG	PEG-lipid	Controls particle size, aggregation, and circulation behavior
Phosphate buffer	pH control	Supports product stability
Sodium chloride	Tonicity adjustment	Supports intravenous administration
Water for injection	Vehicle	Diluent component

The four lipid components are often described as formulation excipients, although they are central to the drug-delivery mechanism. In a lipid nanoparticle or lipid complex product, the excipients determine encapsulation efficiency, particle size, biodistribution, cellular uptake, endosomal escape, storage stability, and infusion compatibility.

How does the Onpattro lipid formulation work?

The Onpattro lipid system uses an ionizable lipid rather than a permanently charged cationic lipid. DLin-MC3-DMA is more protonated under acidic formulation conditions, which supports association with the negatively charged siRNA. At physiological pH, the lipid is less positively charged, reducing toxicity and improving tolerability relative to permanently cationic systems.

The formulation process generally involves rapid mixing of the lipid components in an organic phase with the siRNA in an acidic aqueous phase. This produces nanoscale particles or lipid complexes in which the siRNA is protected from degradation and presented for uptake by hepatocytes.

After intravenous administration, the particles circulate and accumulate in the liver. Hepatocyte uptake is followed by endosomal trafficking. A portion of the siRNA escapes the endosome and enters the RNA-induced silencing complex, where it directs degradation of transthyretin messenger RNA.

The formulation therefore performs four commercial functions:

1. It protects the siRNA during administration.
2. It directs delivery toward the liver.
3. It enables intracellular release.
4. It supports a reproducible sterile injectable product.

What is the FDA regulatory status of Onpattro?

The FDA approved Onpattro in August 2018 for the treatment of the polyneuropathy of hereditary transthyretin-mediated amyloidosis in adults.[1] It was the first FDA-approved siRNA therapeutic and established a regulatory precedent for lipid-enabled RNA delivery.

The FDA label identifies Onpattro as an intravenous infusion administered once every three weeks. Premedication is required to reduce infusion-related reactions. The formulation is supplied as a sterile, preservative-free concentrate and must be diluted in an intravenous infusion bag before administration.[1]

Onpattro regulatory milestones

Date	Event
August 2018	FDA approval for hereditary transthyretin-mediated amyloidosis polyneuropathy
2018	Initial commercial launch in the United States
2019	European Commission approval for hereditary transthyretin amyloidosis with stage 1 or stage 2 polyneuropathy
2021	FDA expanded approval to include cardiomyopathy manifestations associated with hereditary transthyretin-mediated amyloidosis
2022	FDA approval of Amvuttra, a subcutaneous successor product in the same therapeutic area

Onpattro is a drug product, not a biologic. Biosimilar rules therefore do not apply. Any follow-on competition would generally arise through an abbreviated new drug application, a 505(b)(2) application, or a full new drug application, depending on the level of similarity and the proposed indication.

What excipient patents protect Onpattro?

The commercial protection for Onpattro is primarily built around the patisiran sequence, lipid composition, delivery method, manufacturing process, and methods of treating transthyretin amyloidosis. The excipient system may be covered by broader lipid nanoparticle and RNA-delivery patents, but the FDA Orange Book does not provide a complete map of every formulation or manufacturing right relevant to the product.

The central lipid technology is associated with Alnylam’s licensing and intellectual-property relationships involving ionizable lipid systems. Alnylam has disclosed rights connected to the MC3 lipid platform and related lipid nanoparticle technology through agreements and patent portfolios involving third-party technology owners, including Tekmira Pharmaceuticals and subsequent corporate successors.[2][3]

Potentially relevant patent categories include:

Patent category	Protected subject matter	Competitive impact
Ionizable lipid composition	DLin-MC3-DMA and related lipid structures	May constrain use of the same or closely related lipids
Lipid nanoparticle composition	Ratios of ionizable lipid, DSPC, cholesterol, and PEG-lipid	May affect formulation duplication
siRNA sequence	Patisiran sequence and target region	May block exact-copy products
Treatment method	TTR reduction and treatment of hereditary amyloidosis	May affect label carve-outs
Manufacturing process	Mixing, encapsulation, purification, sterile filtration, and fill-finish	Can create process barriers even after composition patents expire
Product specifications	Particle size, encapsulation, potency, and impurity profiles	May increase development and approval burden

Are Onpattro excipients listed in the Orange Book?

The Orange Book lists patents submitted by the NDA holder that the holder represents as covering the approved drug, including drug substance, drug product, or approved method of use. It does not function as a complete excipient database.

An excipient may be relevant to an Orange Book-listed patent if the patent claims the finished drug product or a defined composition containing that excipient. The presence of DLin-MC3-DMA, DSPC, cholesterol, or PEG2000-C-DMG in the FDA label does not by itself establish that each component has a separate Orange Book listing.

For competitive analysis, the Orange Book should be reviewed together with USPTO records, assignment data, court filings, FDA product-specific guidance, and Alnylam’s public patent disclosures. A formulation patent can remain commercially relevant even when a particular excipient is not separately identified in the Orange Book.

When does Onpattro lose exclusivity?

Onpattro’s market exclusivity has multiple layers rather than one single expiration date.

Protection type	Relevance to Onpattro	Timing assessment
New chemical entity exclusivity	Protected the approved active ingredient after 2018 approval	Expired in 2023, subject to regulatory details
Orphan-drug exclusivity	Applied to the approved orphan indication	Runs separately from patent protection
Composition patents	May cover patisiran, lipid components, or combinations	Expiration depends on individual patent and PTA/PTE status
Method-of-use patents	May cover treatment of hereditary transthyretin amyloidosis	Can be challenged or carved out
Formulation patents	May cover lipid ratios, particle properties, or product composition	May delay simple formulation replication
Process patents	May cover manufacturing and purification	Can complicate development without necessarily blocking an alternative process

A precise generic-entry date cannot be inferred from the FDA approval date alone. The relevant date depends on the complete Orange Book listing, patent-term adjustment, patent-term extension, litigation, settlements, orphan exclusivity, and any pediatric exclusivity.

Who could challenge Onpattro patents?

Potential challengers include generic manufacturers, specialty injectable companies, lipid nanoparticle developers, and RNA-therapy companies with manufacturing capabilities. The most credible entrants would need more than siRNA synthesis capacity. They would require:

• A reproducible lipid-complex manufacturing process.
• Sterile injectable production.
• Analytical methods for particle size and encapsulation.
• Demonstrated control of lipid impurities and degradation products.
• A validated potency assay.
• Clinical or regulatory support for a proposed abbreviated or hybrid pathway.
• A strategy for patents covering the siRNA sequence, lipid composition, and treatment method.

A Paragraph IV challenge could target Orange Book-listed patents by alleging noninfringement, invalidity, or unenforceability. A generic applicant could also pursue a section viii statement and omit a patented method of use, although that strategy may be difficult if the protected indication is closely aligned with the product’s principal commercial use.

There is no general biosimilar pathway for Onpattro. The litigation profile is therefore more likely to involve ANDA or 505(b)(2) disputes than biosimilar litigation.

What formulation patents and manufacturing barriers affect Onpattro competition?

The strongest practical barriers may be manufacturing and analytical rather than the availability of the individual lipid ingredients.

Lipid composition and particle quality

Small changes in lipid ratios can affect:

• Encapsulation efficiency.
• Particle-size distribution.
• Free-siRNA levels.
• Hepatic delivery.
• Infusion tolerability.
• Long-term storage stability.
• Batch-to-batch consistency.

A competitor may avoid literal infringement by changing the lipid ratios or substituting a different PEG-lipid. That change can create a new formulation but also introduce new pharmacokinetic and toxicology requirements.

PEG-lipid limitations

PEG2000-C-DMG helps control particle size and aggregation. PEG-lipids can also reduce cellular uptake if used at excessive concentrations and may contribute to accelerated blood clearance or anti-PEG immune responses in some settings. These limitations create commercial demand for:

• Cleavable PEG-lipids.
• Shorter-chain PEG-lipids.
• Non-PEG hydrophilic polymers.
• Zwitterionic surface coatings.
• Biodegradable shielding groups.
• Ligand-directed hepatic delivery systems.

Sterile manufacturing

Onpattro is an intravenous product. Manufacturing must control particulate matter, endotoxin, sterility, bioburden, residual solvents, lipid oxidation, siRNA degradation, and container-closure integrity. The product must also remain stable during dilution and administration.

A supplier with validated continuous or microfluidic mixing, single-use systems, and sterile fill-finish capacity can capture value even without owning a drug product. Contract development and manufacturing organizations can sell:

• Lipid raw materials.
• Preassembled lipid mixtures.
• Drug-product process development.
• Encapsulation and purification services.
• Sterile filtration and fill-finish.
• Stability-indicating analytical packages.
• Comparability support for formulation changes.

What commercial opportunities exist in Onpattro excipients?

The largest opportunities are in platform components that can be used across multiple RNA medicines rather than in Onpattro-specific supply alone.

Ionizable lipid supply

Ionizable lipids are high-value components because they directly affect delivery performance. Suppliers can compete on purity, scalable synthesis, impurity control, regulatory documentation, and intellectual-property freedom to operate.

Commercial differentiation may come from:

• Lower-cost kilogram-scale synthesis.
• Reduced residual-metal and solvent profiles.
• Improved oxidation stability.
• More efficient biodegradation.
• Higher hepatic delivery.
• Reduced complement activation.
• Freedom-to-operate around MC3-related structures.

PEG-lipid and surface-engineering platforms

PEG-lipids are relatively low-concentration components but can control product performance. Suppliers can develop libraries of PEG-lipids with different anchor groups, chain lengths, cleavage rates, and deshielding profiles.

The most valuable products will be platform-compatible materials that allow developers to alter tissue distribution or improve repeat-dose tolerability without redesigning the entire particle.

Helper-lipid alternatives

DSPC is a conventional phospholipid with established pharmaceutical use. Alternative helper lipids may improve membrane packing, endosomal escape, or stability. Opportunities include synthetic phospholipids with tighter impurity specifications and tailored phase-transition characteristics.

Cholesterol alternatives

Cholesterol contributes to particle structure and membrane interaction. Oxidation-resistant sterols, plant-derived alternatives, and engineered sterol analogues may be commercially useful where they improve stability or reduce supply-chain risk.

Analytical and regulatory services

Lipid nanoparticle products require specialized characterization. Service providers can sell methods for:

• Encapsulation efficiency.
• Particle size and polydispersity.
• Lipid identity and purity.
• Free-lipid measurement.
• Residual solvent analysis.
• RNA integrity.
• Potency and gene-silencing activity.
• Oxidative and hydrolytic degradation.
• Extractables and leachables.

These services can create recurring revenue across RNA therapeutics, including siRNA, messenger RNA, gene-editing RNA, and antisense-related delivery systems.

How does Onpattro compare with Amvuttra from an excipient and commercial perspective?

Amvuttra is strategically advantaged because it is administered subcutaneously once every three months, whereas Onpattro requires intravenous infusion every three weeks. The products use different delivery approaches and should not be treated as interchangeable formulations.

Attribute	Onpattro	Amvuttra
Active ingredient	Patisiran	Vutrisiran
RNA class	siRNA	siRNA
Administration	Intravenous infusion	Subcutaneous injection
Dosing frequency	Every three weeks	Once every three months
Delivery strategy	Lipid complex	Conjugate-based hepatocyte delivery
Infusion infrastructure	Required	Generally avoided
Excipient opportunity	Lipid nanoparticle and sterile injectable supply	Conjugate chemistry, stabilizers, and prefilled-device systems
Commercial position	First-generation platform	Later-generation, lower-burden product

The competitive shift reduces the long-term growth opportunity for Onpattro-specific excipients. It increases the value of technologies that solve the same delivery problem through simpler administration, lower dose volume, longer duration, or improved repeat-dose tolerability.

What generic launch risks exist for Onpattro?

A potential generic or follow-on product faces several risks:

1. Exact duplication of the lipid system may trigger composition or formulation claims.
2. A materially different lipid system may require additional clinical evidence.
3. Intravenous administration increases development and commercial complexity.
4. The dominant commercial indication may be protected by method-of-use patents or orphan exclusivity.
5. Payers and physicians may prefer Amvuttra’s subcutaneous dosing.
6. A competing product may need to match stringent particle and potency specifications.
7. A 505(b)(2) strategy may not eliminate clinical comparability requirements.
8. Limited market growth can reduce the economic value of entry.

The most viable entry strategy may be a differentiated product rather than a direct copy. Potential differentiation includes reduced infusion time, lower premedication burden, improved storage, smaller dose volume, alternative lipid chemistry, or an indication not fully covered by existing method-of-use claims.

How strong is the Onpattro excipient patent estate?

The estate is strongest where patents combine the active siRNA, defined lipid composition, delivery characteristics, and treatment method. A patent directed only to a widely used excipient may be easier to design around, while a patent claiming a specific combination of lipid ratios and particle properties may create a more meaningful barrier.

Patent-strength assessment

Factor	Assessment
Active siRNA sequence	Potentially strong against exact-copy products
MC3-related ionizable lipid claims	Potentially significant, depending on claim scope and expiration
Broad lipid nanoparticle claims	Vulnerable to prior-art and written-description challenges
Narrow ratio and particle claims	Stronger against close formulation copies, easier to design around
Method-of-use claims	Commercially relevant where the indication has few alternatives
Manufacturing claims	Useful if the process is difficult to reproduce, but alternatives may exist
Regulatory exclusivity	Time-limited and separate from patent protection
Competitive durability	Reduced by Amvuttra and newer RNA-delivery platforms

The estate should be valued claim by claim. Patent age, terminal disclaimers, patent-term adjustment, prosecution history, continuation practice, and claim construction can materially change the risk assessment.

What licensing deals affect Onpattro and lipid nanoparticle technology?

Alnylam has built its RNA-delivery portfolio through internal development and licensing transactions. Its lipid technology history includes relationships associated with Tekmira and other lipid nanoparticle rights holders. Corporate transactions involving Tekmira, Arbutus Biopharma, and related entities have affected ownership and licensing positions for ionizable lipid and lipid nanoparticle patents.[2][3]

Commercial diligence should examine:

• Whether a license is exclusive or nonexclusive.
• The field of use.
• Geographic scope.
• Sublicensing rights.
• Royalty stacking.
• Milestone obligations.
• Patent-challenge provisions.
• Rights to improvements.
• Rights after termination.
• Control of litigation and prosecution.

For excipient suppliers, a license to manufacture a lipid does not necessarily grant freedom to sell a complete drug product using that lipid. Product-level rights, method claims, and delivery-platform licenses must be assessed separately.

What revenue exposure does Onpattro create for excipient suppliers?

Onpattro creates direct demand for four lipid materials and for sterile injectable manufacturing. Its value to suppliers is greater than the absolute volume of excipient consumed because the product validates a regulatory pathway for lipid-enabled siRNA.

The commercial opportunity has two layers:

• Product-specific supply to Onpattro or follow-on products.
• Platform supply for the broader RNA-therapeutics market.

The second layer is more attractive. A supplier dependent only on Onpattro faces concentration risk from Amvuttra, competing siRNA products, and potential portfolio migration to subcutaneous or conjugate-based delivery. A supplier with a broader lipid portfolio can use Onpattro as a reference product while selling into oncology, cardiometabolic, rare-disease, vaccine, and gene-editing programs.

Key Takeaways

• Onpattro uses DLin-MC3-DMA, DSPC, cholesterol, and PEG2000-C-DMG in a liver-directed intravenous siRNA lipid complex.
• Ionizable lipid chemistry is the highest-value excipient category because it controls encapsulation, endosomal escape, tolerability, and delivery.
• The formulation is protected by a layered estate involving active sequence, lipid composition, delivery, manufacturing, and method-of-use claims.
• Onpattro is not subject to biosimilar competition. Generic entry would likely involve an ANDA, 505(b)(2), or full NDA strategy.
• The FDA label identifies the excipients, but it is not a complete guide to every patent covering the formulation.
• Sterile manufacturing, particle characterization, impurity control, and stability are major technical barriers.
• The strongest commercial opportunities are in improved ionizable lipids, PEG alternatives, analytical services, and scalable lipid nanoparticle manufacturing.
• Amvuttra weakens the long-term commercial case for Onpattro-specific excipient supply but strengthens demand for next-generation RNA-delivery platforms.

FAQs About Onpattro Excipients and Commercial Opportunities

Is DLin-MC3-DMA the most important Onpattro excipient?

Yes. DLin-MC3-DMA is the principal ionizable lipid and has a central role in siRNA encapsulation, hepatic delivery, and endosomal escape. It is more commercially significant than conventional buffer or tonicity excipients.

Can a company sell a generic Onpattro using different lipids?

Potentially, but a different lipid system could require substantial formulation, analytical, and clinical comparability work. It may also avoid some patents while creating new regulatory and performance risks.

Does Onpattro have a biosimilar pathway?

No. Onpattro is a small-molecule siRNA drug product, not a biologic. Follow-on developers would generally assess the ANDA, 505(b)(2), or full NDA pathways.

Are Onpattro’s lipids approved as standalone pharmaceutical excipients?

The regulatory acceptability of each lipid depends on its use, grade, manufacturing controls, route, dose, and product-specific data. Approval in Onpattro does not automatically establish unrestricted use in every drug product.

Is Amvuttra a direct formulation substitute for Onpattro?

No. Amvuttra uses a different delivery strategy and administration route. Its subcutaneous, quarterly dosing profile gives it a commercial advantage, but it is not an identical formulation or regulatory substitute.

References

1. U.S. Food and Drug Administration. (2023). Onpattro (patisiran) injection, prescribing information. FDA.

2. Alnylam Pharmaceuticals, Inc. (2024). Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 for the fiscal year ended December 31, 2023. U.S. Securities and Exchange Commission.

3. Arbutus Biopharma Corporation. (2024). Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 for the fiscal year ended December 31, 2023. U.S. Securities and Exchange Commission.

4. European Medicines Agency. (2023). Onpattro: EPAR product information. EMA.

5. Adams, D., Gonzalez-Duarte, A., O'Riordan, W. D., Yang, C. C., Ueda, M., Kristen, A. V., et al. (2018). Patisiran, an RNAi therapeutic, for hereditary transthyretin amyloidosis. New England Journal of Medicine, 379(1), 11-21.

6. U.S. Food and Drug Administration. (2022). Amvuttra (vutrisiran) injection, prescribing information. FDA.