US Patent 8,287,847: Scope, Claims, Expiration, and Hyperkalemia Patent Landscape

US Patent No. 8,287,847 covers methods of treating hyperkalemia with orally, intestinally, or rectally administered crosslinked alpha-fluoroacrylic acid polymers. The broadest commercial relevance is to calcium-containing, low-swelling potassium-binding polymers associated with patiromer products such as Veltassa.

The patent is method-of-treatment protection, not a standalone composition patent. Infringement requires practice of the claimed hyperkalemia-treatment method with a polymer meeting the structural and, for dependent claims, physical and formulation limitations.

What does US 8,287,847 claim?

The patent contains three independent method claims:

Independent claim	Core subject matter	Principal narrowing element
Claim 1	Treating hyperkalemia with a crosslinked cation-exchange polymer having alpha-fluoride-substituted carboxylic groups	Acid or salt form; oral, intestinal, or rectal administration
Claim 9	Treating hyperkalemia with a crosslinked alpha-fluoroacrylic acid polymer	Broad polymer class, with specified crosslinkers in dependent claims
Claim 17	Treating hyperkalemia with a crosslinked alpha-fluoroacrylic acid polymer containing a calcium counterion	Calcium-containing form

The claims collectively target a polymer that:

Binds potassium in the gastrointestinal tract.
Is administered to treat hyperkalemia.
Contains carboxylic acid groups, or their salts.
Has fluorine attached to the carbon alpha to the carboxylic acid group.
Is crosslinked.
May contain calcium as the counterion.
May have low swelling, bead morphology, and high ionization at colonic pH.

The patent does not claim every potassium-binding polymer. Polymers such as sodium polystyrene sulfonate and sodium zirconium cyclosilicate fall outside the literal structural language unless they independently satisfy the alpha-fluoroacrylic-acid limitations.

How do claims 1, 9, and 17 differ?

Claim 1: structural polymer definition

Claim 1 requires a "crosslinked carboxylic polymer having fluoride attached to the carbon atom alpha to the carboxylic acid group." It also requires administration of a potassium-binding polymer to an animal subject with hyperkalemia.

The claim is broad in its route and subject language. "Animal subject" includes humans but is not limited to humans. The polymer must have the specified fluorinated carboxylic structure and must function as a potassium-binding polymer in the claimed treatment.

Claim 9: alpha-fluoroacrylic acid formulation

Claim 9 uses the more direct phrase "crosslinked alpha-fluoroacrylic acid polymer." This claim omits the calcium limitation and does not require a particular crosslinker in the independent claim.

Its dependent claims identify crosslinkers including:

Divinylbenzene
Ethylene bisacrylamide
N,N'-bis(vinylsulfonylacetyl) ethylene diamine
1,3-bis(vinylsulfonyl)-2-propanol
Vinylsulfone
N,N'-methylenebisacrylamide
Polyvinyl ether
Polyallyl ether
Combinations of those materials

Claim 11 specifically limits the polymer to divinylbenzene crosslinking.

Claim 17: calcium-counterion embodiment

Claim 17 requires a crosslinked alpha-fluoroacrylic acid polymer comprising a calcium cationic counterion. This claim is narrower than claim 9 but more directly aligned with calcium-containing potassium binders.

Claims 18 through 25 add low swelling, crosslinker, bead, human-subject, dosage, and ionization limitations.

What dependent claims add protection?

Claims	Limitation	Commercial or technical significance
2, 3	Swelling ratio below 5 or below 3	Targets controlled-swelling gastrointestinal resin particles
4, 12, 21	Human subject	Removes the broader animal-subject scope
5	Chewable tablet	Covers a specific dosage form, although the claim contains an antecedent-basis issue
6, 13, 22	0.5 to 30 grams per day	Encompasses commercial oral dosing ranges
7, 14, 15, 23, 24	More than 75% ionization at physiological colonic pH	Links polymer performance to colonic potassium exchange
8, 17	Calcium counterion	Narrows the polymer to a calcium-containing salt form
10, 19	Listed crosslinkers	Creates narrower composition-process boundaries
11	Divinylbenzene	Important for products using that crosslinking chemistry
16, 20, 25	Bead form	Targets particle-based oral formulations

Claims 14 and 15 are duplicative. Claims 23 and 24 are also duplicative, as are claims 20 and 25. Those duplications do not automatically invalidate the claims, but they add no meaningful incremental scope.

Does US 8,287,847 cover patiromer?

The claim language appears directed to the polymer technology underlying calcium-containing nonabsorbed potassium binders, including products associated with patiromer. Veltassa is FDA-approved as patiromer sorbitex calcium for treating hyperkalemia in adults and pediatric patients six years of age and older. The product is administered orally and exchanges calcium for potassium in the gastrointestinal tract (U.S. Food and Drug Administration [FDA], 2024).

A literal infringement analysis would require product-specific evidence concerning:

The chemical identity of the polymer backbone.
The position of fluorine relative to the carboxylic acid group.
The crosslinking agent.
The calcium-counterion status.
The swelling ratio.
Bead morphology.
Ionization at colonic pH.
The prescribed route, dose, and treatment indication.

The label alone is not enough to establish infringement of every claim. Claims 1, 9, and 17 require technical polymer information that may not appear in public prescribing information.

What is the patent term and expiration timeline?

The patent was issued on October 16, 2012. Its relevant priority chain reaches back to the mid-2000s, and the patent term is principally governed by the earliest effective nonprovisional filing date rather than the earliest provisional filing date. The nominal term therefore runs into the late 2020s, subject to patent-term adjustment, terminal disclaimers, and any applicable statutory correction.

Event	Date or period
Earliest publicly identified priority period	2006
US patent grant	October 16, 2012
Nominal statutory term	Late 2020s
Patent-term adjustment	Must be confirmed from the USPTO patent record
Patent-term extension	No extension is established from the claim text alone

The grant date does not determine expiration. A precise expiration date requires the USPTO patent-term calculation, including the earliest effective nonprovisional filing date and any patent-term adjustment. A patent expiration estimate based only on the 2012 grant date would be legally incorrect.

What is the Orange Book status of US 8,287,847?

The patent number alone does not establish an Orange Book listing. Orange Book listing is product-specific and depends on whether an NDA holder submitted the patent to FDA under the applicable patent-listing provisions.

For Veltassa, the relevant Orange Book analysis must distinguish:

Patents listed for the approved drug product.
Patents listed for the active ingredient.
Patents listed for the drug substance or polymer.
Formulation patents.
Method-of-use patents.
Patent-listing dates and delisting events.
Any patent identified in a Paragraph IV notice.

A method patent can be listed if it claims an approved method of using the drug. A patent that claims only a manufacturing process or an unapproved use generally has a different listing analysis under FDA rules. The claim set supplied here contains treatment-method claims and does not, by itself, prove that US 8,287,847 is currently listed for Veltassa in the Orange Book (FDA, 2024).

What Paragraph IV challenges could target this patent?

An ANDA applicant seeking approval for a generic calcium-containing potassium binder could use a Paragraph IV certification if it contends that the patent is invalid, unenforceable, or not infringed. Potential positions include:

Noninfringement

A generic applicant could design around the claims by using:

A non-fluorinated polymer.
A fluorinated polymer without fluorine at the alpha carbon.
A different polymer backbone.
A polymer without calcium as the counterion.
A non-bead dosage form where bead claims are material.
A formulation or route that does not satisfy the asserted limitations.

Avoiding a dependent limitation does not avoid an independent claim if the independent claim is otherwise met.

Invalidity

Potential validity theories would focus on:

Anticipation by earlier fluorinated acrylic-acid ion exchangers.
Obviousness based on known ion-exchange resins, crosslinking systems, and potassium-binding therapies.
Written-description support for the full alpha-fluoroacrylic-acid polymer genus.
Enablement across the claimed crosslinkers, counterions, swelling ratios, and dosage forms.
Indefiniteness of terms such as "potassium-binding polymer," "swelling ratio," and "physiological pH in the colon."

The specification’s experimental disclosure, cited prior art, claim construction, and prosecution history would control the strength of these arguments. The claims cannot be assessed solely from their text for a definitive validity conclusion.

Patent-term and listing defenses

An ANDA applicant may also challenge:

Whether the patent remains unexpired.
Whether FDA may rely on the patent to delay approval.
Whether the patent is properly listed.
Whether the approved product practices the claimed method.
Whether a statutory safe harbor applies to preapproval activities.

How strong is the patent estate?

US 8,287,847 is strongest against products that replicate the following combination:

A calcium-containing, crosslinked alpha-fluoroacrylic acid polymer.
Oral treatment of hyperkalemia.
Bead or particle dosage form.
Low swelling.
Dosing within the claimed range.
High ionization in the colon.

Its protection is weaker against competing potassium binders using materially different chemistry.

Product or technology	Relationship to US 8,287,847
Patiromer calcium-based polymer	Potentially close technical relationship; product-specific polymer evidence is required
Sodium zirconium cyclosilicate, Lokelma	Different inorganic crystalline mechanism; generally outside the alpha-fluoroacrylic polymer claims
Sodium polystyrene sulfonate, Kayexalate	Different sulfonated polystyrene chemistry; generally outside the claims
Generic patiromer	Main potential target if it uses the claimed fluorinated polymer and calcium form
Novel non-fluorinated organic resin	Likely design-around route
Intravenous or non-gastrointestinal potassium removal	Outside the claimed oral, intestinal, or rectal administration framework

The estate’s technical value is concentrated in the polymer chemistry rather than in the hyperkalemia indication alone. Hyperkalemia treatment is broad, but the alpha-fluoroacrylic-acid limitation materially narrows the protected technology.

What manufacturing and IP barriers does the patent create?

The patent can raise barriers for a competitor attempting to reproduce the same polymer platform. Relevant manufacturing questions include:

Control of fluorinated monomer purity.
Reproducible crosslink density.
Calcium loading and counterion exchange.
Particle-size distribution.
Swelling-ratio control.
Ionization behavior under colonic conditions.
Batch-to-batch potassium-exchange capacity.
Residual monomer and crosslinker control.
Bead formation and drying.
Stability in the final dosage form.

A competitor may avoid literal infringement through a different polymer architecture, but regulatory comparability and clinical performance may still require substantial development. A chemically different polymer can therefore reduce patent exposure while increasing formulation, manufacturing, and FDA-development risk.

What litigation and settlement issues matter?

The key litigation questions are:

Whether the accused product uses the claimed fluorinated polymer.
Whether the relevant calcium form is present.
Whether the generic applicant made a Paragraph IV certification.
Whether the patent was asserted before FDA approval.
Whether any settlement contains a licensed-entry date.
Whether the settlement includes acceleration, supply, or no-challenge provisions.
Whether later continuations or related patents create a separate entry barrier.

A settlement involving a related Veltassa patent would not necessarily resolve the enforceability or expiration of US 8,287,847. Patent families often contain separate formulation, manufacturing, dosage, and method claims with different expiration dates.

What generic-entry scenarios exist?

Scenario 1: Same polymer, same calcium form

This is the highest litigation-risk scenario. A generic using the same alpha-fluoroacrylic polymer and calcium counterion could face literal infringement allegations under claims 9 and 17, with dependent claims adding further overlap.

Scenario 2: Same therapeutic use, different polymer

A non-fluorinated or differently structured potassium-binding polymer could avoid the core claims. The developer would still face pharmaceutical equivalence, clinical endpoint, and CMC requirements.

Scenario 3: Different counterion

Replacing calcium with sodium, magnesium, or hydrogen may avoid claims requiring calcium, but would not necessarily avoid claims 1 or 9 if the underlying fluorinated polymer remains within those claims.

Scenario 4: Different administration or indication

A product not administered orally, intestinally, or rectally, or not approved for treating hyperkalemia, would have a stronger noninfringement position. That strategy may have limited commercial value because gastrointestinal potassium removal is central to the product class.

Key Takeaways

US 8,287,847 is a method patent directed to crosslinked alpha-fluoroacrylic acid potassium binders.
Claims 9 and 17 are the central commercial claims; claim 17 specifically requires a calcium counterion.
The patent does not broadly cover all potassium binders or all hyperkalemia treatments.
Patiromer-type calcium polymer products present the closest potential overlap.
Lokelma and Kayexalate use materially different technologies and generally fall outside the claimed polymer structure.
The patent’s term extends into the late 2020s, subject to USPTO term calculations.
The claim text does not establish current Orange Book listing, patent-term adjustment, litigation, or settlement status.
Generic risk is highest for products copying the fluorinated polymer and calcium-counterion architecture.
The principal design-around path is a non-fluorinated or structurally different potassium-binding polymer.

FAQs

Does US 8,287,847 cover sodium zirconium cyclosilicate?

No, not on the face of the claims. Sodium zirconium cyclosilicate is an inorganic crystalline potassium binder, not a crosslinked alpha-fluoroacrylic acid polymer.

Can a generic avoid claim 17 by using a sodium counterion?

Potentially. Claim 17 requires a calcium cationic counterion. A sodium-counterion product could avoid that claim, but claims 1 or 9 might remain relevant if the product uses the claimed alpha-fluoroacrylic acid polymer.

Are claims 14 and 15 legally different?

They appear textually identical. Unless prosecution history or claim-correction records establish a meaningful distinction, they add no substantive scope difference.

Does a bead-form product automatically infringe claims 16, 20, or 25?

No. Bead form is only one limitation. The product must also meet the applicable independent claim, including the alpha-fluoroacrylic polymer and hyperkalemia-treatment requirements.

Is a method patent enough to block a generic drug launch?

It can delay or prevent launch if it is properly listed, unexpired, enforceable, and infringed by the proposed product or labeled use. A generic applicant may challenge it through a Paragraph IV certification or use a noninfringing label and formulation strategy.

References

U.S. Patent No. 8,287,847. (2012). Methods of treating hyperkalemia. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2024). Veltassa (patiromer) prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA.
United States Patent and Trademark Office. (2024). Manual of Patent Examining Procedure, Chapter 2700: Patent terms and adjustment. USPTO.
U.S. Food and Drug Administration. (2024). Approved drug product and patent listing requirements. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	1732523	⤷ Start Trial	300924	Netherlands	⤷ Start Trial
European Patent Office	2269589	⤷ Start Trial	CA 2018 00003	Denmark	⤷ Start Trial
European Patent Office	1732523	⤷ Start Trial	300925	Netherlands	⤷ Start Trial
European Patent Office	1732523	⤷ Start Trial	122018000011	Germany	⤷ Start Trial
European Patent Office	1732523	⤷ Start Trial	2018C/004	Belgium	⤷ Start Trial
European Patent Office	1732523	⤷ Start Trial	C01732523/01	Switzerland	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,287,847

Summary for Patent: 8,287,847