US Patent 9,339,551: Scope, Claim Analysis, Expiration, and Diclofenac Patent Landscape

US Patent 9,339,551 protects a twice-daily method of treating pain, particularly osteoarthritis pain, with a 2% diclofenac sodium topical formulation containing dimethyl sulfoxide (DMSO), ethanol, propylene glycol, water, and a specified thickening agent. The patent is method-of-use and formulation-defined; it does not broadly cover every topical diclofenac product.

The nominal patent term runs from the 2011 nonprovisional filing date to November 2031, subject to any patent-term adjustment. The commercial relevance is primarily tied to PENNSAID 2%, a diclofenac sodium topical solution approved by the FDA for osteoarthritis pain. The patent does not create biologic exclusivity, and biosimilar pathways are not relevant because diclofenac is a small-molecule active ingredient.

What does US Patent 9,339,551 protect?

The patent protects a treatment method that requires the simultaneous presence of several formulation, performance, and dosing limitations.

Required element	Claim 1 requirement
Active ingredient	2% w/w diclofenac sodium
Penetration solvent	30% to 60% w/w DMSO
Co-solvent	1% to 15% w/w propylene glycol
Alcohol	1% to 30% w/w ethanol
Other vehicle	Water
Rheology	Viscosity of 500 to 5,000 centipoise
Thickener	Cellulose polymer, carbomer polymer, carbomer derivative, cellulose derivative, or mixture
Dosing	Administration twice daily
Indication	Treatment of pain

A competing product must satisfy every limitation of an asserted claim for literal infringement. A product containing diclofenac sodium but lacking the claimed DMSO range, viscosity, thickener, or twice-daily administration would not literally meet claim 1.

The patent therefore has a narrower scope than a composition patent covering any diclofenac topical formulation. Its protection is concentrated on a specific high-DMSO, thickened topical formulation administered twice per day.

How do the dependent claims narrow the patent scope?

The dependent claims create several formulation-specific claim paths.

Claim	Additional limitation	Commercial significance
2	DMSO about 40% to about 50% w/w	Covers the central DMSO range associated with the marketed formulation
3	DMSO from 40% through 50%, including fractions	Reduces ambiguity around the numerical range
4	Ethanol 23% to 29% w/w	Targets a narrower ethanol range
5	Carbomer polymer, carbomer derivative, or mixtures	Excludes cellulose-only systems
6	Carbopol 971, 981, 941, 1342, or Ultrez 10	Identifies specific commercial thickening agents
7	Glycerine present	Adds a formulation excipient
8	Cellulose polymer, cellulose derivative, or mixtures	Creates a separate cellulose-based claim branch
9	Hydroxypropyl cellulose	Narrows the cellulose branch to a named thickener
10	DMSO 40% to 50%, ethanol 23% to 29%, propylene glycol 10% to 12%	Defines a commercially important formulation window
11	DMSO from 40% through 50%, including fractions	Further specifies claim 10
12	Improved absorption per dose compared with a comparative liquid composition	Adds a comparative performance limitation
13	Pain due to osteoarthritis	Aligns the method with the principal approved use of PENNSAID 2%

Claims 2, 3, 10, and 11 are particularly important because they concentrate the patent around a formulation containing approximately 40% to 50% DMSO, 23% to 29% ethanol, and 10% to 12% propylene glycol. Claims 5 through 9 protect alternative thickener technologies.

What formulation does the patent most closely cover?

The patent most closely covers a viscous, high-DMSO topical diclofenac formulation designed to increase dermal delivery while remaining suitable for twice-daily use.

The commercially relevant formulation profile is:

2% diclofenac sodium;
approximately 40% to 50% DMSO;
approximately 23% to 29% ethanol;
approximately 10% to 12% propylene glycol;
water;
a carbomer or hydroxypropyl cellulose thickener; and
viscosity within 500 to 5,000 centipoise.

PENNSAID 2% labeling identifies diclofenac sodium as the active ingredient and includes DMSO, ethanol, propylene glycol, water, and viscosity-modifying excipients. The final infringement analysis would depend on the approved or actual generic formulation, manufacturing specifications, and directions for use, not on the product name alone. (U.S. Food and Drug Administration, 2024a)

How strong are the independent claims?

Claim 1

Claim 1 is commercially meaningful but technically dense. Its strength comes from the combination of:

a precise diclofenac concentration;
a broad but distinctive DMSO range;
defined co-solvent ranges;
a viscosity limitation;
a thickener limitation; and
twice-daily administration.

The combined limitation set can make design-around more feasible than with a broad composition claim. A challenger could seek to avoid the claim by changing one or more of the following:

reducing DMSO below 30%;
increasing DMSO above 60%;
using a different solvent system;
changing viscosity outside the claimed range;
using a non-cellulose, non-carbomer rheology modifier;
adopting once-daily or other dosing directions; or
using a different diclofenac concentration.

A formulation outside one numerical range may still face a doctrine-of-equivalents argument, but numerical ranges and FDA-approved labeling can create substantial prosecution-history and claim-construction issues.

Claim 12

Claim 12 requires "improved absorption on a per dose basis compared to a comparative liquid composition." This limitation may improve the patent's technical alignment with the invention but can complicate enforcement.

The principal issues are:

what constitutes the comparative liquid composition;
whether absorption is measured in vitro, ex vivo, or in vivo;
whether the comparison is based on total exposure, peak concentration, flux, or another metric;
whether the comparison uses equal diclofenac doses; and
whether the comparison method was disclosed consistently in the patent specification.

Claim 12 may be difficult to apply without a defined comparator and reproducible testing protocol. It is less likely to be the primary claim asserted against a generic unless the patent owner has a clear comparison methodology.

Claim 13

Claim 13 limits the method to pain caused by osteoarthritis. This limitation tracks the FDA-approved indication for PENNSAID 2%. It may support infringement allegations based on a generic label that expressly directs use for osteoarthritis pain.

A generic applicant may attempt a "skinny label" strategy by omitting a patented indication. That strategy depends on whether the remaining label, promotional activity, prescribing instructions, or product design still encourage the patented use. Under 35 U.S.C. §271(e)(2), the content of the ANDA and proposed labeling would be central to any Paragraph IV dispute.

When does US Patent 9,339,551 expire?

The patent issued on May 17, 2016, from an application filed November 4, 2011. Its nominal expiration is calculated from the filing date of the earliest relevant nonprovisional application, producing an expected base expiration in November 2031. The enforceable date may differ if the patent received patent-term adjustment or another statutory term modification. (U.S. Patent and Trademark Office, 2016)

Milestone	Date
Nonprovisional filing	November 4, 2011
Patent publication	May 9, 2013
Patent grant	May 17, 2016
Nominal 20-year expiration	November 2031
Patent-term adjustment	Must be taken from the USPTO patent record and Orange Book listing

The patent should not be described as expiring on its grant anniversary. US utility patent term generally runs 20 years from the earliest effective nonprovisional filing date, not 20 years from issuance.

What is the FDA and Orange Book status of the patent?

US Patent 9,339,551 is relevant to the FDA-approved diclofenac sodium topical solution product PENNSAID 2%. PENNSAID 2% is an NDA product, not an ANDA product, and is approved for topical treatment of osteoarthritis pain. (U.S. Food and Drug Administration, 2024a)

The relevant regulatory structure is:

Regulatory issue	Analysis
Product	PENNSAID 2% topical solution
Active ingredient	Diclofenac sodium
Regulatory pathway	New Drug Application
Dosage form	Topical solution
Primary indication	Osteoarthritis pain
Small-molecule exclusivity	Applicable
Biosimilar exclusivity	Not applicable
Orange Book relevance	Patent and exclusivity listings for the reference NDA
Generic pathway	ANDA with Paragraph IV or other certification, depending on listed rights

FDA Orange Book listings can change through patent-listing updates, delistings, expiration-date corrections, and regulatory actions. The Orange Book is the controlling source for the patent and exclusivity information associated with the reference listed drug at a particular edition date. (U.S. Food and Drug Administration, 2024b)

The patent itself does not establish FDA regulatory exclusivity. Patent rights and FDA exclusivity are separate. Diclofenac sodium was previously marketed in other dosage forms, so the relevant NDA exclusivity analysis depends on the specific PENNSAID 2% approval and any qualifying new clinical investigations, not on the age of diclofenac as an active ingredient.

What Paragraph IV challenges and generic entry risks exist?

A generic applicant seeking approval for a product referencing PENNSAID 2% may need to address listed patents through one of four certifications:

Paragraph I, if no patent is listed;
Paragraph II, if the patent has expired;
Paragraph III, if the applicant will wait until expiration; or
Paragraph IV, if the applicant asserts that the patent is invalid, unenforceable, or not infringed.

A Paragraph IV certification can trigger patent litigation under the Hatch-Waxman Act. The reference sponsor generally has 45 days after receiving notice to file suit. A timely suit can create a 30-month stay of FDA approval, subject to statutory exceptions and court developments. (U.S. Food and Drug Administration, 2024b; 21 U.S.C. §355)

The principal generic-entry scenarios are:

Formulation-matching generic

A generic that closely reproduces the DMSO, ethanol, propylene glycol, thickener, viscosity, and twice-daily profile faces the highest literal-infringement risk. Such a product may require a Paragraph IV challenge or a Paragraph III certification, depending on the patent listing and expected launch date.

Formulation design-around

A product could reduce risk by changing its solvent system, viscosity, thickener, dosing frequency, or active concentration. The commercial problem is that these changes may affect bioavailability, skin tolerability, manufacturing reproducibility, or therapeutic equivalence.

Skinny-label product

A generic could omit a patented osteoarthritis indication if the statutory and regulatory conditions permit. The risk increases if the label still contains instructions that encourage the patented method or if the product's marketing supports use for osteoarthritis.

At-risk launch

A generic company may launch before final resolution of litigation after obtaining FDA approval. That exposes the company to damages, injunctive relief, and possible market disruption if the patent is later upheld.

Which companies are challenging the PENNSAID patent estate?

The commercially relevant challengers are companies that file ANDAs for diclofenac sodium topical solution 2% and submit patent certifications against the PENNSAID reference product. Public patent litigation records have historically included generic-drug companies such as Dr. Reddy's Laboratories and other ANDA sponsors in disputes involving PENNSAID-related patents.

The litigation analysis must distinguish:

cases involving US 9,339,551 specifically;
cases involving related PENNSAID patents;
cases dismissed after settlement;
cases stayed or administratively closed;
cases involving different strengths or dosage forms; and
cases in which the patent was not the sole barrier to approval.

A complaint against a generic manufacturer does not establish that the generic infringes. It confirms only that the NDA holder asserted a listed patent after receiving an ANDA certification.

What related patents protect diclofenac topical products?

The PENNSAID estate should be assessed as a family rather than through US 9,339,551 alone. Relevant protection may include:

formulation patents covering DMSO-based diclofenac compositions;
method-of-use patents covering osteoarthritis pain;
patents covering viscosity and absorption performance;
patents covering specific excipient combinations;
continuation or divisional patents with overlapping claim strategies; and
patents directed to earlier or different PENNSAID strengths.

US 9,339,551 is distinct because its issued claims are method claims requiring the formulation to be administered twice daily. A related patent with composition claims could create a stronger barrier against a product whose label avoids a patented indication. Conversely, a method-only patent may be more vulnerable to a label-based design-around.

A complete freedom-to-operate review should map each patent family by:

Patent characteristic	Business implication
Composition claim	Directly targets the product formulation
Method-of-use claim	Depends heavily on labeling and inducement evidence
Process claim	May affect manufacturing but often is harder to detect
Excipient claim	Can constrain formulation development
Absorption claim	Requires analytical evidence and comparator definition
Continuation claim	May preserve enforcement options after an earlier patent expires
Geographic family member	Determines protection outside the United States

How does the patent compare with broader topical diclofenac protection?

US 9,339,551 is narrower than a patent claiming diclofenac generally and narrower than a patent claiming all topical diclofenac formulations. Its commercial value comes from covering a formulation architecture associated with a branded product.

Protection type	Breadth	Relevance to US 9,339,551
Diclofenac compound patent	Very broad but expired for diclofenac	Not relevant
Any topical diclofenac composition	Broad	Broader than this patent
DMSO-based diclofenac formulation	Intermediate	Closely related
Claimed viscosity and excipient ranges	Narrower	Central to this patent
Twice-daily osteoarthritis method	Narrow	Directly covered by claims 1 and 13
Generic product-specific patent	Product dependent	Potentially overlapping

The patent is strongest against a generic that copies the commercial formulation and label. It is weaker against a product that uses a materially different vehicle, rheology system, concentration, or dosing regimen.

What manufacturing and formulation barriers does the patent create?

The patent creates technical barriers even where a competitor believes it can avoid literal infringement. High-DMSO topical products require control of:

solvent compatibility;
polymer hydration;
viscosity over shelf life;
diclofenac solubility;
container and closure compatibility;
evaporation and water loss;
skin tolerability;
dose uniformity; and
scale-up mixing conditions.

Carbomer and cellulose systems can produce different rheological behavior and manufacturing profiles. A design-around using hydroxypropyl cellulose instead of a carbomer may avoid some dependent claims but remains within the broad thickener category of claim 1 if all other limitations are present.

The twice-daily dosing limitation also links patent risk to regulatory labeling. A formulation that is technically distinct but approved with the same dosing schedule and osteoarthritis indication may still require careful claim-by-claim analysis.

Key Takeaways

US 9,339,551 is a method patent focused on twice-daily treatment of pain with a 2% diclofenac sodium topical formulation.
Claim 1 requires DMSO, ethanol, propylene glycol, water, a specified thickener, a 500 to 5,000 cP viscosity, and twice-daily administration.
Claims 10 and 11 define the most commercially important formulation window: 40% to 50% DMSO, 23% to 29% ethanol, and 10% to 12% propylene glycol.
Claims 6 and 9 protect alternative thickener pathways, including named carbomers and hydroxypropyl cellulose.
Claim 12 may present enforcement complexity because the required absorption comparison depends on the comparator and testing method.
Claim 13 is closely aligned with the PENNSAID 2% osteoarthritis indication.
The nominal expiration is in November 2031, subject to USPTO patent-term adjustment and the controlling Orange Book record.
Generic entrants face the greatest risk when they copy both the formulation and the twice-daily osteoarthritis label.
Biosimilar risk is irrelevant because diclofenac is a small-molecule active ingredient.
The commercial barrier is the combined patent, regulatory, formulation, manufacturing, and labeling estate, not US 9,339,551 in isolation.

FAQs About US Patent 9,339,551 and PENNSAID 2%

Does US 9,339,551 claim the diclofenac molecule itself?

No. Diclofenac is an old active ingredient. The patent claims a formulation-defined method of treatment, not the diclofenac molecule.

Can a generic avoid the patent by using diclofenac potassium?

Potentially, but the analysis would depend on whether the claims require diclofenac sodium and whether the proposed product is therapeutically equivalent to the reference product. Claim 1 expressly requires 2% w/w diclofenac sodium.

Does once-daily dosing avoid US 9,339,551?

It may avoid the twice-daily limitation in claim 1, but the complete product, label, manufacturing process, and related patent family would still require review.

Are Carbopol and Carbomer interchangeable for infringement analysis?

Not automatically. Carbopol is a commercial brand and grade family associated with carbomer polymers. The relevant question is whether the selected material falls within the claim construction of carbomer polymer or carbomer derivative and whether the other claim limitations are met.

Is US 9,339,551 an Orange Book patent?

It is associated with the PENNSAID 2% regulatory and patent estate. The current listing status, expiration date, and use code must be taken from the applicable FDA Orange Book edition.

References

U.S. Food and Drug Administration. (2024a). PENNSAID- diclofenac sodium solution prescribing information. FDA.
U.S. Food and Drug Administration. (2024b). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. FDA.
U.S. Patent and Trademark Office. (2016). United States Patent No. 9,339,551, topical formulations of diclofenac. USPTO.
United States Code. (2024). 35 U.S.C. §§ 154, 271, and 282. U.S. Government Publishing Office.
United States Code. (2024). 21 U.S.C. § 355, new drug applications and abbreviated applications. U.S. Government Publishing Office.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Horizon	PENNSAID	diclofenac sodium	SOLUTION;TOPICAL	204623-001	Jan 16, 2014		DISCN	Yes	No	9,339,551	⤷ Start Trial				USE OF TOPICAL DICLOFENAC FOR TREATING PAIN	⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2007311019	⤷ Start Trial
Brazil	PI0717769	⤷ Start Trial
Canada	2666398	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 9,339,551

Which drugs does patent 9,339,551 protect, and when does it expire?

Summary for Patent: 9,339,551