# United States Patent 5,667,775: Scope, Claims, Expiration and Phosphate-Binder Patent Landscape

US Patent 5,667,775 covers oral administration of hydrophilic, cross-linked aliphatic amine polymers that remove phosphate from patients through ion exchange. The claims are broad composition-by-function method claims encompassing sevelamer-type polymers, including cross-linked poly(allylamine) materials. The patent issued on Sept. 16, 1997, and its 20-year patent term expired on Jan. 29, 2014, based on the relevant priority and filing history. It no longer creates a blocking patent right in the United States.[1]

The patent was central to the original Renagel phosphate binder franchise, later marketed as Renvela after reformulation as sevelamer carbonate. The commercial product is narrower than the claim language. The patent claims cover a large genus of polymers, copolymers, crosslinking agents, counterions and substituted amine structures.

What does US Patent 5,667,775 cover?

US 5,667,775 covers a method of removing phosphate from a patient by orally administering a therapeutically effective amount of a polymeric ion-exchange composition. The claimed polymer must contain hydrophilic aliphatic amine functionality capable of exchanging ions in the gastrointestinal tract.

The patent has 22 claims. Claims 1, 9, 14, 18 and 22 are independent claims. The dependent claims narrow those methods by specifying crosslinking agents, crosslinker concentrations, copolymer structures, alkyl-carbon limits and exchangeable counterions.

Claim group	Principal subject matter	Main limitation
Claims 1-8	Polymer or copolymer used orally to remove phosphate	Broad repeat-unit genus; optional crosslinking
Claims 9-13	Polymer with positively charged amine groups and exchangeable counterions	Requires negatively charged counterions
Claims 14-17	Polymer with substituted or unsubstituted C1-C20 alkyl groups	Carbon-chain limitation
Claims 18-21	Polymer with three independently variable substituents and counterions	More specific charged polymer genus
Claim 22	Hydrophilic cross-linked aliphatic amine polymer	Functional and structural summary claim

The patent does not limit the method to sevelamer hydrochloride, sevelamer carbonate, a particular dosage strength, a particular tablet, or a named commercial product.

How do the independent claims differ?

What is the scope of claim 1?

Claim 1 is a broad method claim directed to orally administering a composition containing at least one polymer or copolymer having the specified repeat unit. The claim permits wide variation in the R substituents, including:

Hydrogen;
Unsubstituted alkyl, alkylamino or aryl groups;
Substituted versions of those groups;
Substituents such as amino, hydroxy, quaternary ammonium, guanidine, urea, halogen and carboxylic acid ester groups.

Claim 1 does not expressly require crosslinking. Claims 2-4 add crosslinking and specify concentration ranges. A polymer that met claim 1 without being cross-linked could theoretically fall within the claim, provided it satisfied the repeat-unit and phosphate-removal limitations.

What is the scope of claim 9?

Claim 9 focuses on a charged polymer in which each X is an exchangeable negatively charged counterion. This language is directed to cationic amine polymers in salt form.

For a sevelamer-type material, the counterion could be chloride, carbonate-related species or another pharmaceutically acceptable anion, depending on the polymer's chemical form and claim construction. Claims 10-13 narrow this group by requiring a hydrogen substituent and by specifying crosslinking.

What is the scope of claim 14?

Claim 14 limits R1 and R2 to substituted or unsubstituted alkyl groups containing one to 20 carbon atoms. This limitation is narrower than the more expansive aryl- and alkylamino-containing alternatives in claim 1.

The claim remains broad because it covers many possible substitution patterns. The method is still defined by administering the polymer to remove phosphate, rather than by a narrowly defined molecular weight, degree of substitution or dosage form.

What is the scope of claim 18?

Claim 18 covers a polymer with three independently variable substituents, R1, R2 and R3, together with exchangeable negatively charged counterions. It is a more elaborate charged-polymer genus than claim 14.

The independent claim reaches polymers with positively charged amine sites that can exchange their counterions for phosphate in the gastrointestinal tract. Claims 19-21 add crosslinking-agent and concentration limitations.

What is the scope of claim 22?

Claim 22 is the shortest and potentially broadest independent claim. It covers:

A method for removing phosphate from a patient by ion exchange;
Oral administration;
A therapeutically effective amount;
A composition containing at least one hydrophilic cross-linked aliphatic amine polymer.

Unlike claims 1, 9, 14 and 18, claim 22 does not identify a detailed repeat-unit formula in the claim text supplied. Its principal limitations are functional and structural: the polymer must be hydrophilic, cross-linked and aliphatic amine-based.

This claim is particularly relevant to sevelamer because sevelamer is a cross-linked poly(allylamine) polymer with amine groups that bind phosphate through ionic exchange and hydrogen bonding.

Does US 5,667,775 cover sevelamer?

Yes. Sevelamer is within the technical genus described by the patent and is the principal commercial product associated with the patent family.

Sevelamer hydrochloride is a nonabsorbed, cross-linked poly(allylamine hydrochloride). Sevelamer carbonate uses carbonate counterions and is the active polymer in Renvela. FDA labeling describes sevelamer as a nonabsorbed phosphate binder that binds dietary phosphate in the gastrointestinal tract and reduces serum phosphorus.[2]

The patent does not require the polymer to be called sevelamer. It instead claims polymer architecture and use. This distinction matters:

A product may infringe a genus claim without using the patentee's product name.
A chemically different polymer may avoid infringement if it falls outside the claimed repeat-unit structures or the hydrophilic cross-linked aliphatic amine limitations.
A polymer that binds phosphate but is not administered orally, or is not used for phosphate removal from a patient, would not satisfy the complete method claim.
A product used for a non-phosphate indication would not meet the claimed therapeutic method.

What formulations are protected by US 5,667,775?

The patent covers compositions administered orally but does not claim a particular tablet, powder, suspension, granule, capsule or sachet in the claims provided.

The likely covered formulation categories include:

Formulation	Potential relationship to US 5,667,775
Sevelamer hydrochloride tablets	Within the claimed method if the administered composition meets the polymer limitations
Sevelamer hydrochloride powder	Same analysis
Sevelamer carbonate tablets	Within the genus if the polymer and ion-exchange limitations are satisfied
Sevelamer carbonate powder	Same analysis
Polymer granules	Potentially covered if orally administered for phosphate removal
Combination products	Potentially covered if the claimed polymer is present and performs the claimed method

The patent does not establish exclusivity over every formulation attribute. Later patents may claim tablet hardness, disintegration, particle size, excipient systems, taste masking, carbonate conversion, manufacturing conditions or dosage regimens.

What crosslinking agents does the patent claim?

Claims 3, 7, 12, 16 and 20 identify a large group of crosslinking agents. The list includes:

Epichlorohydrin;
1,4-butanediol diglycidyl ether;
1,2-ethanediol diglycidyl ether;
1,3-dichloropropane;
1,2-dichloroethane;
1,3-dibromopropane;
1,2-dibromoethane;
Succinyl dichloride;
Dimethyl succinate;
Toluene diisocyanate;
Acryloyl chloride;
Pyromellitic dianhydride.

The dependent claims recite crosslinker concentrations ranging from approximately 0.5% to 75% by weight, with narrower claims covering approximately 2% to 20%. Claims 6-8 use a 1% to 75% range for copolymers.

These ranges are important for validity and infringement analysis. A product containing a different crosslinker may still fall within an independent claim, particularly claim 22, if it is a hydrophilic cross-linked aliphatic amine polymer. The listed-crosslinker claims are narrower and should be analyzed separately.

When did US Patent 5,667,775 expire?

US 5,667,775 expired on Jan. 29, 2014, assuming the patent term reflected the earliest relevant nonprovisional filing date and no effective term adjustment extended the patent.[1]

Event	Date
Earliest relevant priority date	Jan. 29, 1993
US patent issued	Sept. 16, 1997
Approximate 20-year term endpoint	Jan. 29, 2014
Current enforceability	Expired
Current US exclusivity from this patent	None

The expiration date is separate from FDA regulatory exclusivity. FDA approval exclusivity for Renagel and Renvela ended years before or around the period in which generic competition became commercially viable. Patent expiration does not erase historical infringement exposure, damages claims or the importance of related patents, but it eliminates prospective enforcement of this patent itself.

What is the Orange Book status of US 5,667,775?

US 5,667,775 was historically associated with the Renagel product and the sevelamer phosphate-binder franchise. Orange Book listings for Renagel and related sevelamer products included multiple patents covering the polymer, formulations and related product attributes.[3]

The patent is expired and cannot currently block an FDA-approved generic or 505(b)(2) product. A current applicant would instead need to assess:

Unexpired formulation patents;
Manufacturing-process patents;
Particle-size or dosage-form patents;
Method-of-use patents;
Regulatory exclusivity;
FDA product-specific requirements;
Potential non-patent barriers involving chemistry, specifications and bioequivalence.

For a small-molecule or polymeric oral product, the relevant FDA pathway is generally an ANDA under section 505(j), not a biosimilar application under section 351(k).

Were Paragraph IV challenges filed against this patent?

A Paragraph IV certification against US 5,667,775 would have been relevant before its 2014 expiration. After expiration, the patent no longer provides a prospective basis for a Paragraph IV litigation strategy.

Generic sevelamer applicants have faced patent disputes involving later Renagel or Renvela patents, particularly patents directed to formulations, particle characteristics, carbonate forms and manufacturing. The relevant litigation targets have included generic applicants such as Amneal, Dr. Reddy's Laboratories, Lupin and other ANDA filers in disputes involving Sanofi and related entities. Those later disputes should not be conflated with continuing enforceability of US 5,667,775.

The commercial consequence is direct: an applicant today does not need to clear US 5,667,775 as a live patent. It may still need to address it in an abbreviated application record or historical patent analysis, but the expired patent should not support an injunction against launch.

Which companies have challenged the sevelamer patent estate?

The competitive challenge has come from generic manufacturers seeking approval for sevelamer hydrochloride or sevelamer carbonate products. Public disputes involving the broader estate have included Sanofi against ANDA applicants and generic companies such as:

Amneal Pharmaceuticals;
Dr. Reddy's Laboratories;
Lupin;
Other applicants pursuing generic sevelamer products.

The relevant lawsuits generally concerned later patents rather than the expired US 5,667,775 patent. The commercial inquiry is therefore patent-family specific. A conclusion that a generic company challenged a Renagel or Renvela patent does not establish that it challenged, or lost against, US 5,667,775.

How strong is the patent estate for sevelamer?

The individual patent is now legally weak as an enforcement asset because it has expired. Historically, it was strong as a foundational genus patent because it described the core therapeutic concept: oral phosphate removal using cross-linked hydrophilic amine polymers.

Factor	Assessment
Technical breadth	High
Product relevance to sevelamer	High
Claim type	Method of treatment
Dependence on named molecule	Low
Dependence on formulation	Low
Current enforceability	None
Historical blocking value	High
Current generic launch risk from this patent	None
Residual value for freedom-to-operate history	High

The broadest risk during the patent term came from claim 22 and the independent repeat-unit claims. A competitor could have faced infringement exposure even if it used a polymer different from commercial sevelamer, provided the polymer met the claimed structural and functional requirements.

Validity risks would have included written-description and enablement challenges arising from the breadth of the claimed polymer genus. Other potential issues would have included anticipation by earlier ion-exchange polymers, obviousness based on known amine resins and phosphate-binding materials, and claim-construction disputes over "hydrophilic," "aliphatic amine polymer," "therapeutically effective amount" and "removing phosphate."

How does US 5,667,775 compare with competing phosphate-binder patents?

Product	Active material	Main patent landscape	Biosimilar risk
Renagel/Renvela	Sevelamer hydrochloride/carbonate	Foundational polymer, formulation and manufacturing patents	None
Fosrenol	Lanthanum carbonate	Composition, formulation and use patents	None
PhosLo	Calcium acetate	Formulation and method patents	None
Auryxia	Ferric citrate	Composition, use and formulation patents	None
Velphoro	Sucroferric oxyhydroxide	Composition, formulation and manufacturing patents	None

Sevelamer is a nonabsorbed polymeric phosphate binder. Fosrenol, Auryxia and Velphoro are inorganic or coordination-based binders. Their patent estates are chemically distinct. A generic sevelamer applicant generally faces product-specific patent issues, not cross-product patent infringement.

What generic launch risks remain after expiration?

The expired patent creates no direct launch barrier. Remaining risks are concentrated in later rights and regulatory execution.

Formulation and manufacturing barriers

A generic applicant may still need to design around patents claiming:

Sevelamer carbonate preparation;
Conversion from hydrochloride to carbonate;
Polymer particle-size distribution;
Tablet compression and hardness;
Dissolution or disintegration profiles;
Low-moisture or stability-controlled products;
Excipients and coating systems;
Manufacturing sequences;
Impurity controls;
Specific dosage forms.

FDA approval issues

FDA approval depends on pharmaceutical equivalence, quality attributes, product specifications and bioequivalence requirements. For nonabsorbed phosphate binders, conventional plasma pharmacokinetic bioequivalence may not fully capture the relevant regulatory analysis. FDA may require comparative clinical pharmacodynamic, in vitro binding or other product-specific evidence.[4]

Revenue exposure

Renagel and Renvela generated substantial revenue for the originator before generic entry. The foundational patent supported the commercial franchise during the period when sevelamer was differentiated from calcium-based phosphate binders and later from newer noncalcium products. After expiration, revenue exposure shifted from the expired polymer patent to:

Remaining formulation patents;
Brand loyalty and nephrology prescribing;
Supply reliability;
Generic substitution rules;
Payer contracting;
Dosage-form preference;
Manufacturing scale.

The expired patent no longer supports a royalty stream, injunction strategy or exclusivity premium in a US transaction.

What is the geographic coverage of US 5,667,775?

The patent provides rights only in the United States. Corresponding international or foreign-family patents must be evaluated separately by jurisdiction. Expiration, terminal disclaimers, prosecution history and enforceability can differ across Europe, Canada, Japan, Australia and other markets.

A US freedom-to-operate conclusion cannot be transferred automatically to:

European Patent Office member states;
Canada;
Japan;
China;
Australia;
Latin American jurisdictions.

The commercial product may have been protected by separate national patents covering sevelamer chemistry, formulations or manufacturing. Each jurisdiction requires a separate family and legal-status review.

Key Takeaways

US 5,667,775 claims oral phosphate removal using hydrophilic, cross-linked aliphatic amine polymers.
The patent broadly covers sevelamer-type polymers without naming sevelamer as a required molecule.
Independent claims 1, 9, 14, 18 and 22 cover polymer structure, charged counterions, substitution patterns and functional use.
Dependent claims specify crosslinking agents and concentration ranges from approximately 0.5% to 75% by weight, including narrower 2% to 20% ranges.
The patent issued Sept. 16, 1997, and expired Jan. 29, 2014.
It no longer blocks generic sevelamer entry in the United States.
Historical Paragraph IV activity involved the broader Renagel/Renvela patent estate, especially later formulation and manufacturing patents.
No biosimilar pathway applies because sevelamer is a nonbiologic polymeric drug.
Current launch risk is concentrated in later patents, FDA product-specific requirements, formulation design and manufacturing know-how.
The patent remains commercially important as the foundational patent for the sevelamer phosphate-binder concept, but it has no current prospective enforcement value.

FAQs About US Patent 5,667,775 and Sevelamer

Is US 5,667,775 still enforceable?

No. The patent expired on Jan. 29, 2014, and does not currently provide enforceable US exclusivity.

Does US 5,667,775 claim Renvela?

It claims broad methods using polymeric phosphate binders. Renvela's sevelamer carbonate polymer falls within the technical subject matter, but the patent does not claim the Renvela brand or require a specific commercial formulation.

Can a generic sevelamer manufacturer ignore this patent?

For prospective US launch analysis, the patent is expired and does not create an injunction risk. The manufacturer must still evaluate unexpired related patents and FDA requirements.

Is sevelamer subject to biosimilar competition?

No. Sevelamer is regulated as a nonbiologic drug product. Competition proceeds through generic or other abbreviated drug-approval pathways rather than the biosimilar pathway.

What patent issues are most important for a new sevelamer formulation?

The key issues are carbonate conversion, polymer particle size, tablet and powder formulation, manufacturing process, stability, dissolution, impurity profile and any unexpired method-of-use claims.

References

United States Patent and Trademark Office. (1997). Hydrophilic amine polymers as phosphate binders, U.S. Patent No. 5,667,775.
U.S. Food and Drug Administration. (2023). Renvela (sevelamer carbonate) prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations (Orange Book).
U.S. Food and Drug Administration. (2016). Draft guidance on sevelamer hydrochloride tablets and sevelamer carbonate tablets: Product-specific bioequivalence recommendations.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0716606	⤷ Start Trial	CA 2002 00003	Denmark	⤷ Start Trial
European Patent Office	0716606	⤷ Start Trial	SPC/GB02/011 200210	United Kingdom	⤷ Start Trial
European Patent Office	0716606	⤷ Start Trial	SPC004/2002	Ireland	⤷ Start Trial
European Patent Office	0716606	⤷ Start Trial	C00716606/01	Switzerland	⤷ Start Trial
European Patent Office	0716606	⤷ Start Trial	CA 2009 00048	Denmark	⤷ Start Trial
European Patent Office	0716606	⤷ Start Trial	C300428	Netherlands	⤷ Start Trial
European Patent Office	0716606	⤷ Start Trial	91629	Luxembourg	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,667,775

Summary for Patent: 5,667,775