US Patent 8,754,258: Ferric Citrate Intrinsic-Dissolution Patent Scope and Landscape

US Patent 8,754,258 protects orally administered ferric citrate products made from ferric citrate having an intrinsic dissolution rate of at least 1.88 mg/cm²/min. The claims cover tablets, powders, capsules, granules, troches and pills, with dependent claims narrowing the dissolution range to 1.88-4.0 mg/cm²/min or 1.9-4.0 mg/cm²/min. The patent is directed to the physical-performance characteristics of ferric citrate rather than to a particular excipient system, tablet strength or disease indication.

The principal enforcement issue is whether a competing ferric citrate product was made from ferric citrate meeting the claimed intrinsic dissolution-rate threshold. A generic applicant could challenge the patent through a Paragraph IV certification, argue that the dissolution limitation is indefinite or inadequately enabled, or design around the claims by using material below the claimed threshold or a different iron compound.

What does US Patent 8,754,258 claim?

The independent claim requires four elements:

An orally administrable form.
The active material is ferric citrate.
The ferric citrate was prepared from a form having an intrinsic dissolution rate of at least 1.88 mg/cm²/min.
The dosage form is a tablet, powder, capsule, granule, troche or pill.

Claim 1 is therefore a product claim with a manufacturing-history limitation. The phrase “prepared from” is important. It does not expressly require that the finished tablet or capsule itself exhibit an intrinsic dissolution rate of at least 1.88 mg/cm²/min. The claim instead focuses on the ferric citrate starting material used to make the oral dosage form.

Claim	Scope	Practical effect
1	Oral ferric citrate dosage form made from ferric citrate with IDR of at least 1.88 mg/cm²/min	Broadest claim; covers six dosage-form categories
2	Claim 1, with IDR of 1.88-4.0 mg/cm²/min	Narrows the upper boundary
3	Claim 1, with IDR of 1.9-4.0 mg/cm²/min	Excludes the 1.88-1.89 mg/cm²/min interval
4	Claim 1, where ferric citrate has formula C6H5O7Fe	Adds a chemical-identity limitation
5	Claim 1, where the dosage form is a tablet	Most commercially relevant narrowing claim

The claims do not require:

A specific ferric citrate particle size.
A particular polymorph or hydrate.
A specified excipient.
A specified iron content.
A specified dosage strength.
A renal-disease indication.
A phosphate-binding method of use.
A particular manufacturing process after the ferric citrate starting material is selected.

The patent claim set is consequently broader than a conventional tablet-formulation patent in some respects. It does not depend on a particular excipient combination or tablet architecture. Its central limitation is the dissolution property of the ferric citrate input material.

How does the intrinsic dissolution-rate limitation work?

Intrinsic dissolution rate, or IDR, measures the dissolution rate of a substance under specified conditions from a controlled surface area. It is different from ordinary dissolution testing of a finished tablet.

The threshold in claim 1 is quantitative:

Minimum claimed value: 1.88 mg/cm²/min.
Narrow range in claim 2: 1.88-4.0 mg/cm²/min.
Narrow range in claim 3: 1.9-4.0 mg/cm²/min.

A dispute would likely focus on the assay protocol used to measure IDR. Relevant variables may include:

Dissolution medium and pH.
Temperature.
Agitation rate.
Surface-area control.
Sample compaction pressure.
Powder density.
Duration of the test.
Calculation of the linear dissolution phase.
Chemical assay used to quantify dissolved ferric citrate.

A competitor may obtain a result above or below 1.88 mg/cm²/min depending on the protocol. The patent specification and prosecution history would be important in determining the controlling measurement method. A product that tests at 1.87 mg/cm²/min under a validated method may fall outside claim 1, while a product testing at 1.90 mg/cm²/min may implicate claims 1-3.

The threshold creates a technical infringement question rather than a simple label-comparison question. A generic label may identify ferric citrate tablets, but it normally will not disclose the IDR of the source material. Discovery could therefore require manufacturing records, supplier specifications, batch testing and analytical validation.

What dosage forms are protected by US 8,754,258?

Claim 1 expressly covers six dosage-form categories:

Tablets.
Powders.
Capsules.
Granules.
Troches.
Pills.

Claim 5 narrows the protection to tablets. Tablets are commercially significant because Auryxia, the principal U.S. ferric citrate product, is marketed as an oral tablet.

The claim language does not expressly limit the product to immediate-release tablets. A modified-release or delayed-release product could potentially fall within the claims if it is an orally administrable ferric citrate form made from qualifying ferric citrate. The absence of a release-profile limitation broadens the potential reach, subject to claim construction and the patent specification.

A liquid solution is not expressly listed in claim 1. A liquid product could face a scope dispute over whether it is a “powder,” “granule,” “pill,” “capsule,” “tablet” or other claimed form. On the literal language provided, the enumerated forms do not clearly include a ready-to-administer liquid.

What chemical material does the patent cover?

Claim 4 identifies ferric citrate by the formula C6H5O7Fe. The formula corresponds to ferric citrate as identified in the claim set. Claim 4 remains dependent on claim 1, so the material must also be used in an orally administrable form prepared from ferric citrate having the required IDR.

Claim 4 does not independently protect every product containing ferric citrate. A product must satisfy the structural, dosage-form and dissolution-history requirements inherited from claim 1.

The claim does not expressly cover:

Ferrous citrate.
Ferric ammonium citrate.
Sucroferric oxyhydroxide.
Ferric maltol.
Ferric carboxymaltose.
Other non-citrate iron salts.

Those products may compete in the same therapeutic or commercial categories without practicing the claimed ferric citrate limitations.

What is the patent’s relationship to Auryxia and FDA regulation?

Auryxia is ferric citrate, marketed by Keryx Biopharmaceuticals and later associated with Akebia Therapeutics. The FDA approved Auryxia in 2014 for control of serum phosphorus levels in adults with chronic kidney disease on dialysis. The FDA later approved an indication for iron-deficiency anemia in adults with chronic kidney disease not on dialysis. The product is an oral tablet.[1]

The claims in US 8,754,258 are composition and dosage-form claims. They are not limited to the phosphate-binding indication or the iron-deficiency-anemia indication. A product label can therefore practice the claims even if it uses a different indication, provided the product satisfies the ferric citrate and IDR limitations.

FDA approval and patent infringement are separate questions:

Issue	Relevant question
FDA approval	Has FDA approved the product and its proposed labeling?
Orange Book	Is the patent listed against the reference product and relevant dosage form?
Patent scope	Does the product meet the claim limitations?
Generic pathway	Has the ANDA applicant made Paragraph III, Paragraph IV or other certification?
Enforcement	Has the patent holder sued within the statutory period after a Paragraph IV notice?

The Orange Book determines whether a listed patent may create the 30-month stay associated with a Paragraph IV notice. It does not determine the ultimate validity or infringement outcome. Current Orange Book status should be assessed against the FDA’s electronic Orange Book and patent-listing data for Auryxia.[2]

When does US 8,754,258 lose exclusivity?

Patent expiration cannot be calculated reliably from the issue date alone. The controlling term depends on:

The earliest effective nonprovisional filing date.
Any applicable domestic benefit claims.
Patent-term adjustment.
Patent-term extension.
Terminal disclaimers.
Regulatory extensions.
Disclaimer or lapse events.

US 8,754,258 issued on June 17, 2014.[3] Its enforceable term is generally based on 20 years from the earliest effective U.S. nonprovisional application in the priority chain, subject to statutory adjustments under 35 U.S.C. §§ 154 and 156. The patent’s continuity data and USPTO Patent Center records must be used to establish the operative expiration date.[4]

The issue date is not the expiration date. A continuation patent can issue years after the earliest priority filing and still expire based on the earlier application date. Conversely, patent-term adjustment can extend the nominal 20-year term.

Regulatory exclusivity for Auryxia is separate from the patent term. FDA approval exclusivity may expire before or after a particular patent, and an Orange Book-listed patent may continue to affect generic approval after regulatory exclusivity has ended.

What Paragraph IV challenges could target this patent?

A Paragraph IV challenge could attack validity, enforceability or infringement. The most relevant theories are technical and claim-specific.

Anticipation

A challenger would seek prior art showing an orally administrable ferric citrate product made from ferric citrate having an IDR of at least 1.88 mg/cm²/min. A prior-art reference that discloses ferric citrate tablets without the IDR limitation may not anticipate the claim unless the dissolution property is inherent and necessarily present.

Obviousness

The challenger could combine prior art on:

Oral ferric citrate.
Ferric citrate tablets.
Dissolution-rate optimization.
Particle-size control.
Ferric citrate manufacturing.
Phosphate binding or oral iron therapy.

The strongest obviousness case would require evidence that a skilled person would have selected ferric citrate material within the claimed IDR range with a reasonable expectation of achieving the claimed oral dosage form.

Indefiniteness

The IDR limitation may be challenged if the patent does not identify a sufficiently definite and reproducible testing method. The issue would be whether a skilled person can determine, with reasonable certainty, whether a product was made from ferric citrate having an IDR of at least 1.88 mg/cm²/min.[5]

Written description and enablement

A challenger could argue that the specification does not adequately support the full range beginning at 1.88 mg/cm²/min and extending upward, or that it does not enable all oral dosage forms listed in claim 1. The breadth of the claim matters because it covers tablets, powders, capsules, granules, troches and pills without requiring a specific formulation.

Noninfringement

A generic manufacturer could argue that:

Its ferric citrate has an IDR below 1.88 mg/cm²/min.
It uses ferric citrate from a different source.
The source material was not “prepared from” a qualifying form.
Its product is not one of the listed oral forms.
The relevant ferric compound is not the claimed ferric citrate.
The finished product is not made from the material characterized in the patent.

What design-around strategies exist?

The most direct design-around strategy is to use ferric citrate material with an IDR below 1.88 mg/cm²/min. That approach creates manufacturing and consistency challenges because the product must still meet pharmaceutical quality, dissolution and bioavailability requirements.

Other possible design-around routes include:

Strategy	Potential benefit	Principal risk
Use a different iron compound	Avoids ferric citrate limitation	May require a different clinical and regulatory program
Use a liquid product	May avoid enumerated solid dosage forms	Scope may depend on claim construction and equivalence
Use ferric citrate outside the IDR range	Directly targets the numerical limitation	Batch variability may create infringement exposure
Use a different ferric citrate source	May avoid the “prepared from” history	Source qualification and proof may be difficult
Develop a different formulation	May avoid other patents in the estate	Does not necessarily avoid claim 1
Use an alternative indication	Does not necessarily practice method claims	Does not avoid this product claim if product limitations are met

A formulation change alone may not avoid US 8,754,258. The claims do not require a particular excipient system. A tablet using different binders, disintegrants or coatings may still infringe if made from qualifying ferric citrate.

How strong is the patent estate around ferric citrate?

US 8,754,258 should be analyzed as one member of a broader Auryxia-related estate rather than as the complete protection for ferric citrate. A commercial diligence review should separate the estate into the following categories:

Core product claims

These claims cover ferric citrate itself or a defined ferric citrate composition.

Dosage-form and formulation claims

These claims may cover tablets, excipient combinations, particle properties, stability characteristics or dissolution performance. US 8,754,258 is primarily in this category, although its “prepared from” language gives it a manufacturing-history component.

Method-of-use claims

These claims may cover phosphate binding in chronic kidney disease, treatment of hyperphosphatemia or treatment of iron-deficiency anemia.

Manufacturing claims

These claims may cover production, purification, crystallization, particle engineering or control of ferric citrate properties.

Regulatory and commercial protection

FDA approval exclusivity, orphan-drug status if applicable, Orange Book listings, pediatric exclusivity and settlement agreements can affect market entry independently of the patent’s technical scope.

The practical strength of US 8,754,258 is moderate to strong against a conventional ferric citrate tablet if the patent’s IDR assay is reproducible and the manufacturer’s source material falls within the claimed threshold. Its strength is weaker against products using a different iron salt, a liquid dosage form or ferric citrate deliberately manufactured below the threshold.

What litigation and settlement issues affect generic entry?

A Paragraph IV dispute involving this patent would likely produce a patent-specific infringement analysis centered on manufacturing evidence. The label alone may not resolve the case because the label generally does not disclose the IDR of the ferric citrate input material.

The main litigation questions would be:

What test method controls the IDR measurement?
Is the claimed IDR limitation a product limitation, a process limitation or both?
Does “prepared from” require proof of the historical source material?
Can the patent holder rely on batch testing or supplier records?
Is the claimed property inherent in prior-art ferric citrate?
Does the patent specification support the full claimed range?
Are any Orange Book-listed patents still capable of delaying approval?
Does a settlement permit an authorized generic, license, or negotiated entry date?

A settlement may resolve the commercial entry date without producing a judicial ruling on validity. The settlement terms, including any license, authorized-generic arrangement or covenant not to sue, are therefore as important as the public patent docket.

How does US 8,754,258 compare with a typical formulation patent?

US 8,754,258 is broader in formulation design but narrower in raw-material performance than a conventional excipient patent.

Attribute	US 8,754,258	Conventional formulation patent
Core limitation	Ferric citrate IDR and oral dosage form	Specific ingredients or ratios
Excipient dependence	None stated	Usually material
Dosage forms	Six expressly listed forms	Often one or several forms
Manufacturing evidence	Important	Important but usually formulation-focused
Label-based analysis	Limited	Often easier
Design-around	Change material property or active ingredient	Change excipients or process
Main litigation issue	IDR testing and source history	Composition and equivalence

This structure may reduce the value of routine formulation substitutions as a design-around. A competitor could replace the excipient system and still remain within the claim.

Key Takeaways

US 8,754,258 claims oral ferric citrate products made from ferric citrate with an IDR of at least 1.88 mg/cm²/min.
Tablets are the most commercially relevant embodiment and are separately recited in claim 5.
The patent does not require a particular excipient, dosage strength, indication or tablet architecture.
Claims 2 and 3 narrow the IDR range to 4.0 mg/cm²/min, with claim 3 beginning at 1.9 mg/cm²/min.
Claim 4 adds the ferric citrate formula C6H5O7Fe.
The central infringement issue is likely to be the IDR measurement and the source history of the ferric citrate material.
A different excipient system may not avoid infringement.
The strongest design-around options are a different active iron compound, a non-enumerated dosage form or ferric citrate material outside the claimed IDR range.
FDA approval, Orange Book listing, patent term and regulatory exclusivity must be analyzed separately.
The operative expiration date requires the full USPTO priority, continuity, patent-term-adjustment and terminal-disclaimer record.

FAQs About US Patent 8,754,258

Does US 8,754,258 cover all ferric citrate tablets?

No. It covers tablets made from ferric citrate having an intrinsic dissolution rate of at least 1.88 mg/cm²/min, together with the other limitations inherited from claim 1.

Can a generic avoid US 8,754,258 by changing tablet excipients?

Not necessarily. The claims provided do not require a specific excipient system. A tablet with different excipients may still infringe if it uses qualifying ferric citrate.

Is the 1.88 mg/cm²/min threshold measured on the finished tablet?

The claim refers to the IDR of the ferric citrate form from which the oral dosage form was prepared. That wording points to the active-material input rather than ordinary finished-tablet dissolution testing.

Does using ferric citrate for a different indication avoid the patent?

No. The claims provided are not limited to a particular therapeutic indication. A different indication would not avoid the product limitations.

Does patent expiration automatically permit immediate generic sale?

No. Generic launch also depends on FDA approval, applicable Orange Book patents, regulatory exclusivity, litigation outcomes, settlement terms and any other enforceable patent claims in the product’s patent estate.

References

U.S. Food and Drug Administration. (2014). FDA approves Auryxia to treat hyperphosphatemia in patients with chronic kidney disease. FDA.
U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations: Electronic Orange Book. FDA.
United States Patent and Trademark Office. (2014). U.S. Patent No. 8,754,258, Ferric citrate compositions and methods of use. USPTO.
United States Patent and Trademark Office. (2025). Patent Center: Application, continuity and patent-term records for U.S. Patent No. 8,754,258. USPTO.
United States Code. (2023). 35 U.S.C. §§ 112, 154 and 156. Government Publishing Office.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2004213819	⤷ Start Trial
Australia	2006279333	⤷ Start Trial
Australia	2007210090	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,754,258

Summary for Patent: 8,754,258