United States Patent 5,968,976: Lanthanum Carbonate Scope, Expiration, Litigation, and Generic Risk

U.S. Patent No. 5,968,976 protected lanthanum carbonate hydrate compositions containing approximately 3 to 6 waters of crystallization, processes for producing those hydrates, and oral treatment of hyperphosphatemia. The patent covered the active pharmaceutical ingredient used in Fosrenol, but its nominal patent term ended on December 11, 2016. FDA approval of generic lanthanum carbonate products after that date removed the principal patent barrier to competition.[1][2]

The patent did not broadly claim every lanthanum compound or every phosphate binder. Its central limitation was the defined hydrated form of lanthanum carbonate, together with the pharmaceutical, manufacturing, and treatment-use limitations recited in separate claim groups.

What drug does U.S. Patent 5,968,976 protect?

U.S. Patent 5,968,976 protects lanthanum carbonate hydrate for treating hyperphosphatemia, particularly in patients with renal impairment. The protected material has the formula:

La₂(CO₃)₃·xH₂O

where x is from 3 to 6.

The patent is associated with lanthanum carbonate, the active ingredient in Fosrenol, marketed for reducing serum phosphate concentrations in patients with end-stage renal disease.[2][3]

Item	Patent and product data
U.S. patent	5,968,976
Patent subject	Lanthanum carbonate hydrate
Active ingredient	Lanthanum carbonate
Core hydrate range	3 to 6 waters of crystallization
Preferred range	3.5 to 5
Narrowest claimed range	3.8 to 4.5
Principal dosage form	Oral gastrointestinal administration
Therapeutic use	Treatment of hyperphosphatemia
Brand product	Fosrenol
Original U.S. approval	November 24, 2004
FDA application	NDA 021468
Nominal patent expiration	December 11, 2016

What are the independent claims in U.S. Patent 5,968,976?

The patent has three substantive independent claim categories: composition, manufacturing process, and treatment method.

Claim 1: Pharmaceutical composition

Claim 1 covers a pharmaceutical composition containing:

Lanthanum carbonate of the formula La₂(CO₃)₃·xH₂O;
x from 3 to 6;
A pharmaceutically acceptable diluent or carrier; and
A form suitable for administration to the gastrointestinal tract.

This is a composition claim, not a claim to the chemical compound in isolation. A product lacking a pharmaceutical carrier, or a material outside the claimed hydration range, would not literally satisfy every limitation of claim 1.

The phrase "form for administration to the gastrointestinal tract" is directed to pharmaceutical delivery, including oral products and other gastrointestinally administered preparations. The claim does not expressly require a tablet, chewable tablet, powder, sachet, or particular excipient system.

Claims 2 and 3: Narrower hydrate ranges

Claim 2 narrows the water content to 3.5 to 5 molecules of water.

Claim 3 narrows it further to 3.8 to 4.5 molecules of water.

These dependent claims can provide narrower fallback positions if the broader 3-to-6 range is challenged for validity or scope. They also create potential infringement issues involving analytical measurement of hydration state, manufacturing controls, storage conditions, and batch-to-batch variation.

Claim 4: Unit dosage form

Claim 4 requires a unit dosage form providing 0.1 to 20 grams per day.

This limitation does not require one unit to contain the full daily amount. It requires the dosage regimen or unit-dosage presentation to provide an amount within the stated daily range. A competing product could face claim 4 exposure even if its individual tablet strength differs from the branded product, depending on how the dosage instructions and product labeling are construed.

What does claim 5 protect in the lanthanum carbonate manufacturing process?

Claim 5 protects a process that follows three defined steps:

Lanthanum oxide is reacted with hydrochloric acid to form lanthanum chloride.
The lanthanum chloride solution is reacted with an alkali-metal carbonate to produce a wet cake of lanthanum carbonate octahydrate.
The wet cake is dried to obtain lanthanum carbonate containing 3 to 6 waters of crystallization.

Claim 6 specifies sodium carbonate as the alkali-metal carbonate.

Why the process claims matter

The process claims are narrower than the composition claims because they require a particular sequence and intermediate. A manufacturer using a different lanthanum source, a different precipitation route, a different carbonate reagent, or a process that does not produce the specified octahydrate wet cake may avoid literal infringement of claim 5.

The process claims also create potential issues under 35 U.S.C. § 271(g) if a product made outside the United States by a patented process is imported into the United States. Whether section 271(g) applies depends on whether the imported lanthanum carbonate is made by the claimed process and whether the statutory exceptions apply.[4]

The process claims do not cover every method of manufacturing lanthanum carbonate. Their value depends on whether the claimed route is commercially necessary, preferred for controlling hydration, or used by a competitor.

What do claims 7 through 10 protect?

Claims 7 through 10 are method-of-treatment claims.

Claim 7 covers administering an effective amount of lanthanum carbonate hydrate containing 3 to 6 waters of crystallization to treat hyperphosphatemia.

Claims 8 and 9 narrow the hydrate range to 3.5 to 5 and 3.8 to 4.5, respectively.

Claim 10 requires oral administration.

These claims are directed to treatment conduct rather than the composition itself. Their practical enforcement value depends on the accused product's labeling, promotional materials, instructions for use, and the ability to establish induced or contributory infringement.

A generic product labeled for the same hyperphosphatemia indication could create method-of-use exposure while the patent remains enforceable. FDA labeling rules and the scope of any approved indication would therefore be relevant to a Paragraph IV strategy.

How strong is the patent estate for lanthanum carbonate?

The patent estate represented by U.S. 5,968,976 was technically significant but structurally limited.

Patent feature	Scope assessment
Hydrated active ingredient	Broad within 3 to 6 waters, but limited to that hydration range
Preferred hydrate	Stronger technical specificity at 3.5 to 5 and 3.8 to 4.5
Pharmaceutical composition	Requires carrier or diluent and gastrointestinal administration
Dosage limitation	Adds 0.1 to 20 g/day requirement
Manufacturing route	Narrow, sequence-dependent process claim
Treatment method	Covers hyperphosphatemia treatment using the specified hydrate
Oral use	Expressly covered by claim 10
Chemical genus	Does not broadly cover all lanthanum salts
Unhydrated material	Not expressly covered by the claims
Lanthanum chloride or lanthanum hydroxide	Not covered as the claimed active ingredient
Other phosphate binders	Not covered

The main technical vulnerability is the reliance on a measurable hydration range. Hydrated inorganic compounds can change water content during drying, storage, milling, granulation, and testing. A dispute could involve the appropriate analytical method, sample conditioning, crystalline phase, and whether the claimed range describes a fixed stoichiometric compound or an average composition.

The main legal vulnerability is claim breadth relative to prior art concerning lanthanum carbonate, hydrated lanthanum salts, phosphate binding, and pharmaceutical use of lanthanum compounds. The patent's narrower ranges and process sequence would likely provide stronger positions than the broadest composition language if validity were contested.

When did U.S. Patent 5,968,976 lose exclusivity?

The patent's nominal expiration date was December 11, 2016, as reflected in FDA Orange Book patent information.[1] The date is based on the patent's applicable twenty-year term and is distinct from the patent's issue date of October 19, 1999.

FDA exclusivity timeline

Event	Date
Patent issued	October 19, 1999
Fosrenol FDA approval	November 24, 2004
Five-year NCE exclusivity	Through November 24, 2009
Nominal U.S. patent expiration	December 11, 2016
Post-expiration generic market	2017 onward

The patent was not the only regulatory protection relevant to Fosrenol. FDA new chemical entity exclusivity initially prevented submission of an ANDA for five years after approval, subject to statutory exceptions. That regulatory exclusivity ended well before the patent expiration date.[3]

Any pediatric exclusivity extension would have required confirmation in FDA exclusivity records. It should not be treated as a patent-term extension. Patent term extension under 35 U.S.C. § 156 also requires a specific regulatory record and is separate from ordinary patent expiration.[4]

What was the Orange Book status of lanthanum carbonate?

Fosrenol was listed in the Orange Book under NDA 021468. U.S. Patent 5,968,976 was listed for the product and had an expiration date of December 11, 2016.[1]

The Orange Book listing did not mean that every later lanthanum carbonate product infringed every claim. It identified a patent associated with the approved drug and created the statutory framework for ANDA applicants to submit a Paragraph IV certification before expiration.

Because the patent has expired, the Orange Book listing no longer creates a continuing patent block. Current generic applicants do not face a live 5,968,976 patent barrier, although other patents, regulatory requirements, or manufacturing rights could matter independently.

Which companies challenged the Fosrenol patent?

ANDA applicants seeking approval before patent expiration could challenge the listed patent through a Paragraph IV certification. Publicly available FDA Orange Book records establish the listed patent and its expiration, but they do not alone provide a complete litigation history for every ANDA applicant.

The commercially relevant post-expiration landscape has included generic manufacturers offering lanthanum carbonate chewable tablets and related presentations. Generic approval was possible after the patent expired, subject to FDA bioequivalence, chemistry, manufacturing, and labeling requirements.

A Paragraph IV certification would have created potential Hatch-Waxman litigation under 35 U.S.C. § 271(e)(2), with a possible thirty-month stay if the NDA holder filed a timely infringement action. After December 11, 2016, the principal listed-patent stay risk from U.S. 5,968,976 ended.[5]

What formulation patents protect Fosrenol beyond U.S. 5,968,976?

U.S. 5,968,976 is primarily a hydrate, composition, process, and treatment patent. It is not a detailed chewable-tablet formulation patent. The claims do not specify:

A particular sweetener;
A particular flavor system;
A particular compression force;
A defined tablet hardness;
A specific particle-size distribution;
A particular disintegrant;
A particular granulation process; or
A controlled-release delivery system.

Later patents or applications could have addressed tablet formulation, taste masking, particle engineering, manufacturing controls, or alternative lanthanum carbonate forms. Those rights must be evaluated separately by family, claim scope, expiration date, terminal disclaimers, Orange Book listing, and legal status. They should not be assumed to be covered by U.S. 5,968,976.

The core 5,968,976 claims also do not expressly require the branded Fosrenol chewable-tablet excipient formulation. A generic manufacturer could potentially use a different excipient system while still infringing if its product contains lanthanum carbonate within the claimed hydration range and meets the remaining limitations.

What generic entry risks existed before patent expiration?

Before December 11, 2016, generic entry faced four principal risks:

Composition infringement. A product containing lanthanum carbonate hydrate within the 3-to-6 range could fall within claims 1 through 3.
Method-of-use infringement. A label for treating hyperphosphatemia could implicate claims 7 through 10.
Process infringement. A manufacturer using the specified lanthanum oxide, hydrochloric acid, carbonate precipitation, octahydrate wet-cake, and drying sequence could implicate claims 5 and 6.
Regulatory delay. A Paragraph IV lawsuit could trigger the Hatch-Waxman thirty-month stay.

After expiration, the primary risks shifted from patent infringement to regulatory and commercial execution. Those risks include demonstrating pharmaceutical equivalence, controlling hydration state, satisfying dissolution requirements, matching the reference product's dosage form, and obtaining supply-chain approval.

How does U.S. 5,968,976 compare with competing phosphate-binder patents?

Product or class	Main protection type	Relationship to 5,968,976
Fosrenol, lanthanum carbonate	Hydrate composition, process, treatment	Subject of 5,968,976
Sevelamer carbonate/hydrochloride	Polymer composition and use patents	Chemically distinct
Calcium acetate	Composition and formulation rights	Chemically distinct
Sucroferric oxyhydroxide	Iron-based compound and formulation rights	Chemically distinct
Ferric citrate	Iron-citrate composition and treatment rights	Chemically distinct
Aluminum-based binders	Older composition and use rights	Chemically distinct

The patent did not block development of other phosphate binders. Its competitive effect was concentrated within the lanthanum carbonate market.

What manufacturing and geographic barriers remain?

The U.S. patent expired, but geographic patent risk must be evaluated independently. A patent family may contain corresponding rights in Europe, Japan, Canada, Australia, and other jurisdictions with different expiration dates, claim amendments, supplementary protection certificates, or legal-status outcomes.

The U.S. claims also create a manufacturing-screening issue. A company should map:

The lanthanum starting material;
The acidification step;
The carbonate reagent;
The precipitation intermediate;
The water content after drying;
The analytical method for hydration;
The manufacturing location; and
The final product's U.S. import route.

Because the U.S. patent expired in 2016, those process issues no longer create infringement liability under this patent in the United States. They may still matter for foreign manufacture in jurisdictions where related rights remain active, or for freedom-to-operate analysis against later patents.

What is the current commercial significance of the patent?

U.S. 5,968,976 no longer provides enforceable U.S. exclusivity. Its historical value was substantial because it protected the hydrate form used in Fosrenol across composition, process, and treatment claims. Its commercial value after expiration is limited to patent-history analysis, validity review, freedom-to-operate records, and historical generic-entry analysis.

Revenue exposure was tied to Fosrenol sales in the U.S. lanthanum carbonate market before generic entry. After expiration, pricing pressure and market-share erosion became more important than litigation over this patent. A precise revenue estimate requires company-period financial data and should not be inferred solely from the patent record.

Key Takeaways

U.S. Patent 5,968,976 covers lanthanum carbonate hydrate containing 3 to 6 waters of crystallization.
The preferred claimed ranges are 3.5 to 5 and 3.8 to 4.5 waters.
The patent includes composition, manufacturing-process, and hyperphosphatemia-treatment claims.
Claim 5 is materially narrower because it requires lanthanum oxide, hydrochloric acid, carbonate precipitation, an octahydrate wet cake, and drying.
Claim 10 expressly requires oral administration.
Fosrenol was approved under NDA 021468 on November 24, 2004.
The nominal patent expiration date was December 11, 2016.
The patent no longer blocks U.S. generic lanthanum carbonate entry.
Later formulation or process patents must be analyzed separately.
Current U.S. risk is primarily regulatory, manufacturing, commercial, and related-patent risk rather than infringement risk under 5,968,976.

FAQs About U.S. Patent 5,968,976

Is U.S. Patent 5,968,976 still enforceable?

No. Its nominal U.S. patent term ended on December 11, 2016.

Does the patent cover lanthanum carbonate octahydrate?

The process claims refer to producing a wet cake of lanthanum carbonate octahydrate. The final claimed composition must contain 3 to 6 waters of crystallization, not necessarily eight.

Does the patent cover lanthanum carbonate powder?

Potentially, if the powder is a pharmaceutical composition with the claimed hydrate range, a pharmaceutically acceptable carrier or diluent, and a gastrointestinal administration form. The patent does not automatically cover every industrial or nonpharmaceutical powder.

Can a generic company use a different manufacturing process?

Yes, after expiration of U.S. 5,968,976. Before expiration, a different process could have reduced risk under the process claims, but it would not necessarily have avoided the composition or method claims.

Is Fosrenol protected by biosimilar exclusivity?

No. Lanthanum carbonate is a small-molecule inorganic active ingredient, not a biologic. Biosimilar approval pathways do not apply. Generic products proceed through the ANDA framework rather than the biosimilar pathway.

References

U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
U.S. Patent and Trademark Office. (1999). U.S. Patent No. 5,968,976: Lanthanum carbonate. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2004). Fosrenol approval letter and prescribing information, NDA 021468. FDA.
United States Code. (2024). 35 U.S.C. §§ 154, 156, 271, and 271(g).
United States Code. (2024). 21 U.S.C. § 355(j).

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9506126	Mar 25, 1995

PCT Information
PCT Filed	March 19, 1996	PCT Application Number:	PCT/GB96/00575
PCT Publication Date:	October 03, 1996	PCT Publication Number:	WO96/30029

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0817639	⤷ Start Trial	SPC/GB06/036	United Kingdom	⤷ Start Trial
European Patent Office	0817639	⤷ Start Trial	PA2008005	Lithuania	⤷ Start Trial
European Patent Office	0817639	⤷ Start Trial	PA2008005,C0817639	Lithuania	⤷ Start Trial
Austria	209923	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,968,976

Summary for Patent: 5,968,976