United States Patent 5,753,706: Claim Scope, Expiration, and Ferric Citrate Patent Landscape

US Patent No. 5,753,706 covers the use of ferric citrate, ferric acetate, or combinations of the two as phosphate binders, including oral dosage forms containing approximately 500 mg to 1,000 mg per dose. Its claims also address phosphate control in renal failure and metabolic acidosis. The patent is expired and no longer provides an enforceable barrier to generic or competing ferric citrate products. Commercial risk now depends primarily on later patents covering formulation, manufacturing, dosing, product composition, and approved methods of use.

What does US Patent 5,753,706 protect?

US 5,753,706 protects three related subject areas:

Therapeutic methods using ferric citrate or ferric acetate to control phosphate retention.
Oral pharmaceutical compositions containing approximately 500 mg to 1,000 mg of those compounds per dose.
Treatment of renal-failure patients for serum phosphate metabolism and metabolic acidosis.

The claims do not require a particular brand, tablet design, capsule design, excipient, dissolution profile, manufacturing process, or ferric citrate purity specification.

Claim group	Claims	Main subject matter	Key limitation
General phosphate-retention methods	1-5	Administration of ferric citrate, ferric acetate, or both	Hyperphosphatemia or predisposition to hyperphosphatemia
Oral dosage composition	6-8	Oral composition containing ferric citrate or ferric acetate	Approximately 500-1,000 mg per dose plus excipient
Renal failure and acidosis methods	9-13	Control of serum phosphate metabolism and metabolic acidosis	Patient must be suffering from renal failure

The patent is a use-and-composition patent. It is not primarily a process patent or a product-by-process patent.

How broad are the independent claims?

Claim 1: phosphate-retention treatment

Claim 1 covers administering a therapeutically effective amount of:

Ferric citrate;
Ferric acetate; or
A combination of ferric citrate and ferric acetate.

The patient must either have hyperphosphatemia or be predisposed to developing a hyperphosphatemic condition.

The claim does not expressly require:

Renal failure;
Dialysis;
A specific serum phosphate threshold;
Oral administration;
A particular frequency of administration;
A tablet or capsule;
A specific ferric-to-citrate ratio; or
A specific patient age or disease stage.

Because claim 1 is not limited to renal failure, it reaches a potentially broad patient population. Claim 2 narrows the method to oral administration. Claims 3 and 4 separately identify ferric citrate and ferric acetate.

The main functional terms are “controlling phosphate retention” and “therapeutically-effective amount.” These terms would likely be interpreted in light of the specification and clinical context rather than as unrestricted use of any amount of an iron compound.

Claim 6: oral composition

Claim 6 requires an oral dosage form containing:

Approximately 500 mg to approximately 1,000 mg per dose of ferric citrate, ferric acetate, or both; and
A pharmaceutically acceptable excipient.

This claim is narrower than claim 1 because it requires a composition in oral dosage form and a specified amount range. Claims 7 and 8 limit the active compound to ferric citrate or ferric acetate, respectively.

A product could avoid literal infringement of claim 6 if its per-dose amount falls outside the stated range, although the doctrine of equivalents could become relevant depending on the facts. The claim also raises a technical issue: whether the 500 mg to 1,000 mg amount is measured as the iron compound, elemental iron, or another defined composition basis. The patent specification and prosecution history would control that interpretation.

Claim 9: renal failure, phosphate metabolism, and metabolic acidosis

Claim 9 requires treatment of a patient suffering from renal failure by administering ferric citrate, ferric acetate, or a combination to control:

Serum phosphate metabolism; and
Metabolic acidosis.

The use of “and” creates a potential claim-construction issue. A court could require proof that the treatment is directed to both serum phosphate metabolism and metabolic acidosis, rather than phosphate control alone. Claims 10 through 13 narrow the claim to oral administration, the 500 mg to 1,000 mg dosage range, ferric citrate, or ferric acetate.

What technical subject matter is covered?

The patent’s technical center is the use of ferric salts as gastrointestinal phosphate-binding agents. Ferric citrate and ferric acetate can bind dietary phosphate in the gastrointestinal tract, reducing phosphate absorption and increasing fecal phosphate elimination.

The claims cover the active pharmaceutical concept rather than a narrowly defined formulation. The estate therefore sits at the intersection of:

Nephrology;
Chronic kidney disease;
Dialysis-associated hyperphosphatemia;
Phosphate-binding therapy;
Iron-containing oral medicines; and
Metabolic acidosis management.

The claims do not expressly cover iron-deficiency anemia treatment. That indication was later associated with ferric citrate products such as Auryxia, but it is outside the express scope of the claims reproduced above.

When did US 5,753,706 expire?

US 5,753,706 expired in December 2015 based on its underlying patent term. The patent was issued on May 19, 1998, and its term ran approximately 20 years from the relevant nonprovisional filing or priority framework. The patent was therefore no longer an enforceable exclusion right when later generic competition was assessed.

Event	Date
Earliest relevant filing and priority period	1994-1995 period
Patent issued	May 19, 1998
Patent publication	1998
FDA approval of Auryxia, ferric citrate	November 2014
Approximate expiration of US 5,753,706	December 2015

The precise term calculation should be confirmed against the USPTO patent-term record and any terminal disclaimer or adjustment. The commercial conclusion is unchanged: US 5,753,706 is expired and cannot independently support a current injunction against a generic product.

What was the FDA status of ferric citrate?

The FDA approved ferric citrate, marketed by Keryx Biopharmaceuticals as Auryxia, in November 2014 for control of serum phosphorus levels in adults with chronic kidney disease on dialysis. The FDA later approved Auryxia for treatment of iron-deficiency anemia in adults with chronic kidney disease who are not on dialysis.[1]

The first approved indication was closely aligned with the phosphate-binding subject matter of US 5,753,706. The later anemia indication depended on separate clinical and regulatory positioning and was not directly described by the claims listed here.

Regulatory item	Status
Active ingredient	Ferric citrate coordination compound
Brand	Auryxia
Sponsor at initial approval	Keryx Biopharmaceuticals
Initial FDA approval	2014
Initial indication	Serum phosphorus control in adults with CKD on dialysis
Later indication	Iron-deficiency anemia in adults with CKD not on dialysis
Regulatory pathway for generics	ANDA, not biosimilar pathway

Ferric citrate is a small-molecule chemical product. A biosimilar pathway does not apply. Any generic competitor would ordinarily pursue an abbreviated new drug application, subject to the reference product’s exclusivity and listed patent protections.

What was the Orange Book status of US 5,753,706?

US 5,753,706 may have been relevant to the historical patent position surrounding ferric citrate, but it is not a current enforceable Orange Book barrier because it has expired. Current commercial analysis must separate this legacy patent from later patents listed for Auryxia.

An expired patent can remain relevant to:

Historical Paragraph IV disputes;
Prior-art analysis;
Prosecution-history interpretation;
Patent-family tracing;
Validity challenges against later patents; and
Freedom-to-operate analysis involving older products.

It cannot support a current 30-month stay or a current infringement injunction.

Orange Book analysis for Auryxia should focus on later listed patents covering the approved product, dosage forms, formulations, or methods of use. Listing status changes over time, and a patent’s presence in an older Orange Book edition does not establish current enforceability.

Which later patents are more important than US 5,753,706?

The commercially relevant ferric citrate estate developed after US 5,753,706. Later patent families generally addressed narrower and more product-specific subject matter, including:

Ferric citrate pharmaceutical compositions;
Tablet and oral dosage forms;
Excipients and manufacturing controls;
Dosing regimens;
Treatment of iron deficiency;
Treatment of chronic kidney disease populations;
Stability and dissolution characteristics; and
Product formulations associated with Auryxia.

The later estate is more important to generic-entry analysis because those patents could remain in force after the 2015 expiration of US 5,753,706.

Patent category	Typical claim focus	Commercial relevance
Early use patents	Ferric salts for phosphate binding	Mostly expired or weak as current barriers
Product patents	Ferric citrate composition or defined iron content	Can affect generic formulation design
Formulation patents	Tablets, excipients, coating, stability, dissolution	Can support Orange Book listings
Method-of-use patents	CKD, dialysis, anemia, dosing populations	Can create skinny-label or carve-out issues
Manufacturing patents	Preparation, particle properties, consistency	Can create process and sourcing barriers
Regulatory patents	Approved-use claims linked to labeling	Relevant to ANDA certification and launch timing

Known public patent records identify later ferric citrate patents associated with Keryx and its successors, including US 6,906,063 and US 8,093,423. Those patents must be analyzed separately from US 5,753,706 because they may have different expiration dates, claim limitations, and Orange Book treatment. Patent-family continuity does not automatically preserve the term or scope of the earlier patent.

What formulation patents protect ferric citrate products?

A formulation patent may protect the commercial product even when the basic phosphate-binding use patent has expired. Relevant claim elements can include:

Ferric citrate amount per tablet;
Elemental iron content;
Tablet weight;
Inactive ingredients;
Binder and disintegrant selection;
Film coating;
Moisture control;
Dissolution profile;
Stability under storage conditions;
Particle-size distribution; and
Manufacturing sequence.

US 5,753,706 has limited formulation specificity. Claim 6 requires an oral dosage form, a 500 mg to 1,000 mg per-dose amount, and an excipient, but it does not recite a proprietary excipient system or a specific tablet architecture.

A generic manufacturer could therefore design around the claim by using a different dosage amount, delivery format, or product composition, subject to the scope of later patents and FDA bioequivalence requirements.

What method-of-use patents affect generic entry?

Method-of-use patents can remain commercially relevant after a broad phosphate-binding patent expires. For ferric citrate, the main method categories are:

Serum phosphorus control in dialysis patients;
Phosphate reduction in chronic kidney disease;
Iron-deficiency anemia in non-dialysis CKD;
Dosing according to serum phosphate response;
Dose titration;
Administration with meals; and
Use in defined renal-function populations.

A generic sponsor may seek approval with labeling that omits patented indications. This is commonly referred to as a section viii carve-out or skinny label. The feasibility of that strategy depends on whether the patented use is required by the remaining FDA-approved label or embedded in prescribing information that cannot be practically omitted.

Because claims 1 and 9 are broad and expired, they do not create a current method-of-use barrier. Later, narrower method patents may still create litigation risk if a proposed label directly encourages the patented use.

Were Paragraph IV challenges relevant?

Paragraph IV certifications would have been relevant to any unexpired listed patents for Auryxia, not to US 5,753,706 after its expiration.

A generic applicant filing an ANDA for ferric citrate could certify that a listed patent is:

Invalid;
Unenforceable; or
Not infringed.

The brand owner could then file an infringement action within 45 days, potentially triggering a 30-month stay under the Hatch-Waxman framework.[2]

For US 5,753,706 specifically:

A Paragraph IV certification cannot revive the expired patent.
The patent cannot support a new 30-month stay.
The patent can remain relevant as prior art against later patents.
The patent’s disclosure may be used to challenge later claims for obviousness or lack of written description.

What litigation and settlement issues affect ferric citrate?

The principal litigation risk for ferric citrate products has historically involved later patents associated with Auryxia rather than the original 5,753,706 patent. The key issues in such disputes typically include:

Whether the generic formulation practices a listed composition claim;
Whether an ANDA label induces infringement of a method claim;
Whether a formulation patent is valid over earlier ferric-salt disclosures;
Whether the patent claims are limited to a specific ferric citrate form;
Whether the generic product can launch after a patent expiration date; and
Whether a settlement permits an agreed entry date before patent expiration.

Any settlement date must be tested against the actual patent claims, pediatric exclusivity, regulatory exclusivity, and applicable antitrust rules. A settlement involving later Auryxia patents would not extend the term of US 5,753,706.

How strong is the patent estate represented by US 5,753,706?

Strengths

The patent had meaningful historical breadth because it covered:

Two ferric salts;
Combination therapy;
Oral administration;
Broad patient categories;
A defined unit-dose range; and
Renal failure and metabolic acidosis.

Claim 1 was especially broad because it did not require dialysis or a particular formulation.

Weaknesses

The patent also had structural weaknesses:

Ferric salts were known chemical entities.
Phosphate binding by metal-containing compounds was an established therapeutic concept.
The claims use functional terms such as “controlling phosphate retention.”
The composition claim is limited by a relatively simple dosage-range and excipient requirement.
The patent has expired.
The claims do not cover later product-specific features that may distinguish a commercial ferric citrate tablet.

From a current enforcement perspective, the estate strength is zero for US 5,753,706 because the patent is expired. From a historical validity perspective, the broad claims could have faced obviousness and enablement arguments based on prior art involving phosphate binders and iron salts.

What generic launch risks remain?

A generic ferric citrate launch faces several separate risks:

Risk	Current significance
US 5,753,706 infringement	None after expiration
Later composition patents	Potentially significant
Later formulation patents	Potentially significant
Method-of-use patents	Depends on label and indication
FDA exclusivity	Depends on the relevant product and approval history
Bioequivalence	Significant for ANDA approval
Elemental iron equivalence	Important for product characterization
Manufacturing consistency	Important for approval and commercial supply
Patent litigation	Depends on current Orange Book listings
Settlement restrictions	Product-specific and patent-specific

The primary generic strategy is likely to combine a formulation design-around with Paragraph IV challenges to any unexpired listed patents and a section viii carve-out for protected methods where feasible.

How does US 5,753,706 compare with later ferric citrate patents?

Attribute	US 5,753,706	Later ferric citrate patents
Primary focus	Broad use and oral composition claims	Product, formulation, process, and specific-use claims
Active compounds	Ferric citrate and ferric acetate	Often ferric citrate-centered
Dose limitation	Approximately 500-1,000 mg in selected claims	May specify elemental iron, tablets, or dosing schedules
Patient population	Broad hyperphosphatemia and renal failure populations	More defined CKD, dialysis, or anemia populations
Current status	Expired	Some families may have had later expiration dates
Generic relevance	Historical and prior-art relevance	Current launch and litigation relevance
Biosimilar relevance	None	None, because ferric citrate is a small molecule
Orange Book impact	Historical only if previously listed	Potentially current, depending on listing and term

What geographic coverage did the patent provide?

US 5,753,706 provided protection only in the United States. It did not directly control commercial activity in:

The European Union;
Canada;
Japan;
China;
Australia; or
Other jurisdictions.

Foreign counterparts would require separate patent numbers, claim analysis, and term calculations. The expiration of the US patent does not establish the status of foreign family members. Conversely, foreign patent rights would not support a US infringement action.

Key Takeaways

US 5,753,706 covers ferric citrate and ferric acetate for phosphate retention, oral dosage forms, and renal-failure-related phosphate and acidosis control.
Claims 1 and 9 are broad method claims; claim 6 is the principal composition claim.
The patent is expired, approximately as of December 2015.
It is not a current barrier to generic ferric citrate entry.
No biosimilar pathway applies because ferric citrate is a small-molecule drug.
Current risk is concentrated in later Auryxia-related patents covering formulations, compositions, manufacturing, and method of use.
Paragraph IV analysis should focus on unexpired Orange Book-listed patents, not US 5,753,706.
A generic entrant may consider formulation design-around, Paragraph IV certification, and section viii label carve-outs.
The patent’s historical value remains relevant to prior-art and obviousness challenges against later ferric citrate patents.

FAQs About US Patent 5,753,706 and Ferric Citrate

Is US 5,753,706 still enforceable against a ferric citrate generic?

No. The patent expired in approximately December 2015 and cannot independently support a current infringement action.

Does US 5,753,706 cover Auryxia by brand name?

No. The claims cover active compounds, therapeutic uses, and a broad oral composition concept. They do not claim the Auryxia brand or a proprietary commercial label.

Does the patent cover ferric citrate for iron-deficiency anemia?

No. The reproduced claims address phosphate retention, phosphate metabolism, metabolic acidosis, and renal failure. They do not expressly claim treatment of iron-deficiency anemia.

Can a generic use ferric acetate instead of ferric citrate to avoid the patent?

Not during the patent term, because the claims expressly cover ferric acetate. After expiration, the patent no longer blocks either compound, although later patents may apply to ferric citrate products.

Does expiration of US 5,753,706 eliminate all patent risk for ferric citrate?

No. Later patents may cover the commercial formulation, manufacturing method, dosage regimen, or approved indication. A current freedom-to-operate review must examine those later patent families separately.

References

U.S. Food and Drug Administration. (2014). FDA approves Auryxia to control serum phosphorus levels in patients with chronic kidney disease on dialysis. FDA.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Patent and Trademark Office. (1998). U.S. Patent No. 5,753,706: Pharmaceutical compositions and methods for controlling phosphate levels. U.S. Department of Commerce.
U.S. Patent and Trademark Office. (2006). U.S. Patent No. 6,906,063: Ferric citrate compositions and methods of use. U.S. Department of Commerce.
U.S. Patent and Trademark Office. (2012). U.S. Patent No. 8,093,423: Ferric citrate compositions and methods of use. U.S. Department of Commerce.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	400264	⤷ Start Trial
Australia	5441998	⤷ Start Trial
Australia	723091	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,753,706

Summary for Patent: 5,753,706