US Patent 8,551,520: Hydrocodone Controlled-Release Dosage Form Patent Scope and Patent Landscape

US Patent 8,551,520 protects once-daily, solid oral hydrocodone tablets that combine a compressed matrix with specified in-vitro dissolution behavior and, in most claims, a defined 24-hour pharmacokinetic profile. The patent is assigned to Purdue Pharma L.P. and is associated with extended-release hydrocodone products, including Hysingla ER and related hydrocodone formulations.

The patent’s practical value is concentrated in three limitations: the matrix tablet architecture, the six-point dissolution profile, and the C24/Cmax ratio. A competing product must generally satisfy all limitations of at least one unexpired claim to create literal infringement risk.

What does US Patent 8,551,520 protect?

The patent protects a solid oral controlled-release hydrocodone dosage form in which:

Hydrocodone or hydrocodone bitartrate is incorporated into a compressed tablet matrix.
The matrix contains enough controlled-release material to support once-daily administration.
The product meets defined dissolution windows at 1, 4, 8, 12, 18, and 24 hours.
Claims 1-17 and 19 also require a specified C24/Cmax ratio, except claim 18.
Certain dependent claims require specific excipients, including cellulose derivatives, hydrophobic materials, fatty-acid glycerides, microcrystalline cellulose, or hydroxypropylcellulose.

The patent does not claim every extended-release hydrocodone tablet. The claimed product must satisfy the structural, dissolution, dosage, and pharmacokinetic limitations recited in the relevant claim.

Patent identification

Item	Detail
Patent	US 8,551,520
Title	Controlled release hydrocodone formulations
Assignee	Purdue Pharma L.P.
Grant date	October 8, 2013
Technology	Once-daily extended-release hydrocodone matrix tablets
Active ingredient	Hydrocodone or hydrocodone bitartrate
Dosage form	Compressed solid oral tablet
Nominal patent term endpoint	March 30, 2027, subject to any applicable patent-term adjustment, terminal disclaimer, or other USPTO adjustment
Relevant FDA products	Extended-release hydrocodone products, including Hysingla ER
Regulatory pathway	Prescription opioid product regulated under the Federal Food, Drug, and Cosmetic Act

The nominal expiration date is based on the patent family’s 2007 nonprovisional filing date and the standard 20-year patent term. The controlling expiration date should be verified against the USPTO patent-term data and the applicable Orange Book listing.

How many independent claims does US 8,551,520 have?

The patent has three independent claims: claims 1, 15, and 18.

Claim	Independent?	Principal scope
1	Yes	Hydrocodone or pharmaceutically acceptable salt; matrix tablet; dissolution profile; C24/Cmax of about 0.55-1.0
15	Yes	Hydrocodone bitartrate equivalent to 0.5-1,250 mg hydrocodone; same dissolution profile; C24/Cmax of about 0.55-1.0
18	Yes	Hydrocodone bitartrate equivalent to 0.5-1,250 mg hydrocodone; same dissolution profile; no C24/Cmax limitation in the claim

Claim 18 is commercially significant because it omits the pharmacokinetic limitation. A product could avoid claims 1 and 15 by failing to meet the claimed C24/Cmax range, yet still face claim 18 if it meets the required dose, matrix, tablet, and dissolution limitations.

What are the key claim limitations?

Matrix tablet requirement

The dosage form must contain a matrix that is compressed into a tablet. This requirement distinguishes the claims from certain multiparticulate systems, capsules containing drug-coated beads, liquid formulations, transdermal systems, and other delivery platforms.

The claim language does not require a particular manufacturing process. Direct compression, wet granulation, dry granulation, or another process could potentially satisfy the claim if the resulting product has the claimed matrix and performance characteristics.

Controlled-release material

The controlled-release material must be present in an amount sufficient to make the dosage form suitable for once-daily administration. The claims identify broad classes of materials, including:

Gums
Cellulose ethers
Acrylic resins
Waxes
Shellac
Oils

Dependent claim 7 narrows the cellulose category to alkylcellulose, hydroxyalkylcellulose, or carboxyalkylcellulose. These categories can encompass commonly used hydrophilic and hydrophobic matrix polymers, depending on the product composition and claim construction.

Dissolution profile

The claimed in-vitro release profile is:

Test time	Claimed hydrocodone release
1 hour	0% to about 35%
4 hours	About 10% to about 70%
8 hours	About 20% to about 75%
12 hours	About 30% to about 80%
18 hours	About 40% to about 90%
24 hours	Greater than about 60%

The test conditions are also part of the claim:

USP Basket Method
100 rpm
900 mL aqueous buffer
pH between 1.6 and 7.2
37°C

A non-infringement analysis must therefore compare the accused product under the specified test method and conditions. Testing under a different apparatus, agitation speed, buffer volume, or temperature may not answer the claim question.

The ranges overlap substantially. A product that releases 20% at four hours, 50% at eight hours, 65% at 12 hours, 80% at 18 hours, and 90% at 24 hours could fall within multiple release limitations. The profile is not defined by a single release point.

C24/Cmax limitation

Claims 1-17 and 19 require a ratio between hydrocodone concentration at 24 hours and maximum concentration:

Claim 1: about 0.55 to about 1.0
Claim 2: 0.55 to 0.85
Claim 3: 0.55 to 0.75
Claim 4: 0.60 to 0.70
Claim 5: 0.70 to 0.85
Claim 16: 0.55 to 0.85
Claim 19: 0.55 to 0.75

Claims 13 and 14 specify that the ratio may be measured after a first administration to an individual patient or to a patient population. This creates potential evidentiary questions concerning subject selection, dose, food conditions, sampling time, statistical treatment, and whether the limitation is evaluated using individual or population pharmacokinetic data.

The overlapping dependent claims create narrower fall-back positions. For example, a product with a C24/Cmax ratio of 0.65 could fall within claims 1, 2, 3, and 4, assuming all other limitations are met.

What formulations are protected by the patent?

The dependent claims identify a broad family of matrix excipients.

Claim	Formulation limitation
6	Gums, cellulose ethers, acrylic resins, waxes, shellac, or oils
7	Alkylcellulose, hydroxyalkylcellulose, or carboxyalkylcellulose
8	Hydrophobic material with melting point of about 30°C to 200°C
9	Fatty acid, fatty alcohol, glyceryl ester, wax, polyalkylene glycol, or mixture
10	Glyceryl ester of a fatty acid
11	Microcrystalline cellulose
12	Microcrystalline cellulose and hydroxypropylcellulose

These claims provide formulation-specific positions beyond the broad independent claims. A generic developer using a similar hydrophobic matrix or cellulose-based release system may face increased risk if its composition and dissolution data also meet the independent claim requirements.

The claims do not require a particular tablet strength in claims 1-14. Claims 15-19 require hydrocodone bitartrate equivalent to approximately 0.5 mg to 1,250 mg of hydrocodone. That range is unusually broad relative to commercial tablet strengths and could cover a large number of development candidates if the other limitations are satisfied.

What is the Orange Book status of US 8,551,520?

US 8,551,520 has been associated with extended-release hydrocodone products, including Hysingla ER. The relevant product is Hysingla ER, an extended-release hydrocodone bitartrate tablet marketed by Purdue Pharma L.P. The FDA-approved labeling identifies Hysingla ER as a once-daily extended-release opioid analgesic tablet (FDA, 2023).

The Orange Book analysis must distinguish between:

A patent listed against an NDA.
A patent that claims the approved product.
A patent that remains unexpired.
A patent that has not been disclaimed, invalidated, or removed.
A patent that remains relevant to a particular ANDA strength or formulation.

FDA Orange Book listings are regulatory listings, not determinations that every claim is valid or infringed. The patent’s enforceability and scope remain subject to patent litigation, claim construction, validity challenges, and possible prosecution-history estoppel.

When does US 8,551,520 lose exclusivity?

The nominal patent expiration date is March 30, 2027, based on the patent family’s filing chronology. The effective date may differ if the patent has patent-term adjustment, a terminal disclaimer, or another USPTO-recorded modification.

Other exclusivity periods are separate from the patent term:

Exclusivity type	Relevance
Patent exclusivity	Potentially extends through the applicable 2027 patent expiration date
New chemical entity exclusivity	Generally not expected for hydrocodone, an established active ingredient
Three-year clinical-investigation exclusivity	May apply to an NDA or new dosage form for the applicable regulatory period
Orphan-drug exclusivity	Not generally applicable to extended-release hydrocodone
Controlled-substance restrictions	Affect manufacturing, distribution, quotas, and compliance, but do not extend patent term

A generic applicant could face a patent barrier after FDA regulatory exclusivity ends if the patent remains listed and enforceable.

Which companies are challenging the hydrocodone patent estate?

The principal commercial challenge mechanism is an ANDA containing a Paragraph IV certification. A generic applicant may assert that the listed patent is invalid, unenforceable, or not infringed. The NDA holder can file a Hatch-Waxman action within 45 days, triggering an automatic stay of FDA approval for up to 30 months, subject to statutory exceptions and court events (21 U.S.C. § 355).

Public litigation involving extended-release hydrocodone products has included Purdue Pharma and generic manufacturers seeking approval for hydrocodone products. The relevant cases have involved product-specific ANDAs and may address multiple Purdue patents, not only US 8,551,520. A case involving another patent in the same product portfolio does not establish the validity or enforceability of this patent.

The principal litigation issues are likely to include:

Whether the proposed generic has the claimed dissolution profile.
Whether the generic contains a qualifying matrix.
Whether the C24/Cmax ratio is a claim limitation requiring clinical proof.
Whether the claims are indefinite because of terms such as “about,” “suitable for once-a-day administration,” or the pharmacokinetic measurement framework.
Whether the claims are obvious in view of earlier extended-release opioid technologies.
Whether the patent adequately supports the full dose and formulation breadth claimed.
Whether prosecution amendments limit the available scope under the doctrine of equivalents.

How strong is the patent estate for Hysingla ER?

US 8,551,520 has meaningful claim breadth but also carries technical proof requirements.

Strengths

Claim 18 omits the C24/Cmax limitation.
The dissolution profile covers broad release windows.
The matrix limitation can encompass multiple excipient classes.
Claims 15-19 cover a broad hydrocodone-equivalent dose range.
The patent combines formulation structure and product performance, making simple composition-only design-arounds less reliable.

Vulnerabilities

The claims depend heavily on measurable performance characteristics.
“About” ranges can create claim-construction disputes.
The C24/Cmax limitations may invite reproducibility and statistical challenges.
The broad dose range may face written-description or enablement scrutiny if the specification does not support the full scope.
Prior-art extended-release matrix tablets and hydrocodone formulations may support obviousness arguments.
A generic product may be engineered outside one or more dissolution windows while preserving once-daily dosing.

The strongest claim for enforcement is likely claim 18 because it does not require a C24/Cmax result. The strongest design-around opportunity is to alter the release profile, tablet architecture, or active-ingredient form while maintaining therapeutic performance.

What generic launch risks exist?

A generic applicant faces four principal launch scenarios:

Scenario	Commercial consequence
Paragraph IV challenge succeeds	FDA approval may proceed before patent expiration, subject to other listed patents
Paragraph IV litigation settles with an agreed entry date	Launch occurs on the settlement date, often before patent expiration
Patent upheld and infringed	Approval may be delayed until expiration or an agreed license date
Non-infringing formulation approved	Launch may proceed if all other regulatory barriers are cleared

A non-infringing product could attempt to:

Use a dissolution profile outside one or more claimed ranges.
Use a non-matrix dosage architecture.
Use a capsule or multiparticulate system rather than a compressed matrix tablet.
Avoid the specified C24/Cmax range.
Use a different hydrocodone salt or dosage form, subject to regulatory equivalence requirements.
Rely on a formulation that does not contain the listed dependent excipients.

The risk is cumulative because a product that avoids US 8,551,520 may still encounter continuation patents, other Orange Book-listed patents, trade-secret restrictions, controlled-substance manufacturing requirements, or regulatory deficiencies.

How does US 8,551,520 compare with formulation and method-of-use patents?

US 8,551,520 is primarily a formulation and performance patent. It does not principally claim treatment of pain as a medical method. Its infringement analysis focuses on the composition and measured behavior of the dosage form.

A method-of-use patent would instead focus on administering hydrocodone for a specified indication, patient group, dosing schedule, or clinical outcome. Such patents can create separate litigation exposure but may be addressed through a section viii statement when the relevant indication is carved out, subject to FDA acceptance and the scope of the approved labeling.

This patent also differs from manufacturing patents. Manufacturing claims may protect granulation, coating, compression, or process-control steps even if a competing product does not use the same process. US 8,551,520 generally reaches the finished dosage form rather than every method used to produce it.

What is the competitive landscape for once-daily hydrocodone?

The relevant competitive field includes:

Hysingla ER, an extended-release hydrocodone bitartrate tablet.
Zohydro ER and successor extended-release hydrocodone products.
Extended-release oxycodone products.
Hydromorphone extended-release products.
Abuse-deterrent opioid formulations.
Non-opioid analgesics and multimodal pain therapies.

The commercial value of the patent depends on the continuing market for extended-release hydrocodone, the availability of generic substitutes, opioid prescribing controls, state restrictions, abuse-deterrent expectations, and payer preferences.

The patent does not provide exclusivity over hydrocodone as an active ingredient. Immediate-release hydrocodone products, combination products, and technically distinct extended-release systems can compete outside the precise claim scope.

What litigation and settlement issues matter most?

A settlement involving US 8,551,520 would typically address:

An agreed generic launch date.
Whether the generic may launch through an authorized-generic arrangement.
Patent claims included in the release.
Covenants concerning future formulations.
Whether the settlement covers only the named ANDA or a broader product family.
Allocation of litigation costs and commercial supply rights.

The existence of a settlement does not establish patent validity. The commercial entry date must be read together with the settlement agreement, court order, FDA approval status, and all other listed patents.

Key Takeaways

US 8,551,520 is a formulation and performance patent for once-daily hydrocodone matrix tablets.
Claims 1, 15, and 18 are independent.
Claim 18 is the broadest practical claim because it does not require a C24/Cmax limitation.
The claimed dissolution profile is defined at six time points under specified USP Basket Method conditions.
Claims 15-19 cover hydrocodone bitartrate equivalent to approximately 0.5 mg to 1,250 mg hydrocodone.
Dependent claims protect cellulose-based, hydrophobic, fatty-acid, wax, microcrystalline-cellulose, and hydroxypropylcellulose matrices.
The nominal patent expiration is March 30, 2027, subject to USPTO patent-term adjustments and disclaimers.
Generic entry requires analysis of both this patent and any related continuation, formulation, method-of-use, or manufacturing patents.
A successful Paragraph IV challenge, a settlement, or a non-infringing formulation could permit entry before patent expiration.
The key technical design-around variables are tablet architecture, excipient system, dissolution profile, and pharmacokinetic behavior.

FAQs

Is US 8,551,520 a patent on hydrocodone itself?

No. It claims specified extended-release hydrocodone dosage forms, not hydrocodone as a molecule.

Does a product need to meet every dissolution range to infringe?

Yes. An accused product must satisfy all limitations of the asserted claim. For the independent claims, that includes the applicable release limitations at each listed time point.

Can a capsule avoid US 8,551,520?

Potentially. The claims require a matrix compressed into a tablet. A capsule-based product may avoid literal infringement of that limitation, although other patents may apply.

Does claim 18 require a C24/Cmax ratio?

No. Claim 18 includes the dissolution profile and hydrocodone-bitartate dose range but does not expressly require the C24/Cmax limitation.

Does FDA approval establish that a generic does not infringe this patent?

No. FDA approval and patent infringement are separate questions. A generic applicant’s patent certification and any resulting litigation determine the patent-related approval path.

References

Food and Drug Administration. (2023). Hysingla ER prescribing information. U.S. Department of Health and Human Services. https://www.accessdata.fda.gov
Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book. U.S. Department of Health and Human Services. https://www.accessdata.fda.gov/scripts/cder/ob/
United States Patent and Trademark Office. (2013). United States Patent No. 8,551,520: Controlled release hydrocodone formulations. https://patents.google.com/patent/US8551520
United States Code. (2024). 21 U.S.C. § 355: New drugs. https://uscode.house.gov/
United States Patent and Trademark Office. (2024). Patent term adjustment and patent term information. https://www.uspto.gov/patents/laws/adjustment-of-patent-term-extension-recovery-act-1999-actstevenson-wydler-technologyr/ patent-term-adjustment-patent-term-extension-recovery-act-1999-act-stevenson-wydler-technologyr/

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2002227383	⤷ Start Trial
Australia	2738302	⤷ Start Trial
Brazil	0115382	⤷ Start Trial
Canada	2427815	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,551,520

Summary for Patent: 8,551,520