United States Patent 6,576,665: Claim Scope, Expiration, Litigation, and Calcium Acetate Patent Landscape

U.S. Patent No. 6,576,665 protected a specific calcium acetate phosphate-binder product architecture: compressed calcium acetate caplets, sized for hard capsules, with controlled bulk density and rapid dissolution. The patent did not protect calcium acetate itself, phosphate binding generally, or all calcium acetate dosage forms. It expired in January 2021, eliminating current U.S. patent-based generic-entry barriers. Its commercial importance was historically tied to PhosLo and related calcium acetate capsules.

What does U.S. Patent 6,576,665 protect?

The patent claims a calcium acetate composition or method with four cumulative technical requirements:

Calcium acetate is used to bind or absorb phosphorus in the gastrointestinal tract.
The calcium acetate has a specified bulk density.
The material is compressed into a caplet sized to fit inside a specified capsule.
At least 85% dissolves within 15 minutes under the specified USP dissolution test conditions. [1]

The central independent claim is claim 1:

Limitation	Claim requirement	Scope implication
Active ingredient	Calcium acetate	Does not cover non-calcium phosphate binders
Therapeutic function	Binding phosphorus in the gastrointestinal tract	Directed to phosphate-binder use
Bulk density	About 0.55-0.75 kg/L	Numeric formulation limitation
Dosage form	Compressed caplet inside a capsule	Excludes ordinary powder-filled capsules unless they contain the claimed caplet
Capsule design	Capsule volume optimized	Requires a dimensional or volume relationship
Dissolution	At least 85% in no more than 15 minutes	Performance limitation
Test conditions	USP <711>, 50-100 RPM, Apparatus 1 or 2	Broadens testing alternatives but introduces measurement questions

The claim is therefore a combination claim. A product must satisfy all material limitations to infringe literally. A calcium acetate capsule lacking the claimed caplet structure, bulk-density range, or dissolution profile would fall outside the literal scope of claim 1.

How are claims 1 through 15 organized?

The claims divide into composition claims and method claims.

Composition claims

Claims 1 through 11 cover the product.

Claim 1 is the broadest composition claim.
Claims 2 and 3 narrow claim 1 by specifying calcium acetate quantity or bulk density.
Claims 4 through 9 add capsule size and dosage-specific limitations.
Claim 10 independently recites approximately 667 mg of anhydrous calcium acetate in a #0 capsule.
Claim 11 independently recites approximately 333.5 mg of anhydrous calcium acetate in a #2 capsule.

The principal commercial dosage configuration is the #0 capsule containing approximately 667 mg of anhydrous calcium acetate. The smaller #2 capsule configuration divides the dose into approximately half-size units.

Method claims

Claims 12 through 15 cover administering the claimed calcium acetate composition to bind phosphorus.

Claim 12 is the broadest method claim.
Claim 13 focuses on the approximately 667 mg/#0 capsule configuration.
Claim 14 narrows bulk density to 0.60-0.70 kg/L.
Claim 15 addresses the smaller capsule configuration.

The method claims do not create a separate patent on treating hyperphosphatemia with calcium acetate generally. They require administration of a composition containing the same formulation, density, capsule, and dissolution characteristics.

What are the most important claim limitations?

Bulk-density limitation

The claimed bulk-density range is about 0.55-0.75 kg/L, with a preferred range of 0.60-0.70 kg/L.

This limitation is directed to powder handling and dose packing. Calcium acetate with a lower bulk density may require a larger capsule or multiple capsules. A higher-density material may alter compression, dissolution, or capsule dimensions.

The range is potentially important in infringement analysis because bulk density must be measured using an appropriate and reproducible procedure. The claims do not, in the supplied text, identify a detailed measurement protocol such as tapped density versus untapped bulk density. That creates possible evidentiary disputes, particularly where a generic manufacturer uses different sampling, vibration, or compaction conditions.

Caplet-in-capsule limitation

The claimed product is not a conventional powder-filled capsule. The calcium acetate is compressed into a caplet, and the caplet is placed inside a hard capsule.

The specification-specific capsule sizes are:

Claim group	Capsule	Calcium acetate amount
Claims 4-6, 10, 13	#0	Approximately 667 mg anhydrous basis
Claims 7-9, 11, 15	#2	Approximately 333-354 mg, depending on hydration state

The phrase “optimizes the volume of the capsule” is functional and potentially subjective. In practice, infringement would likely focus on whether the compressed unit is dimensioned to fit within the specified capsule and whether the product uses substantially the claimed capsule capacity.

Dissolution limitation

The claims require at least 85% dissolution within 15 minutes under USP <711> conditions at 50-100 RPM using Apparatus 1 or 2.

This is a significant narrowing feature. A calcium acetate product could have the same ingredient, dosage strength, and capsule size but avoid literal infringement if it fails the claimed dissolution threshold. Conversely, a manufacturer cannot reliably avoid the patent merely by selecting a different dissolution apparatus if the product meets the limitation under either permitted apparatus.

The breadth of “50 to 100 RPM” and “Apparatus 1 or 2” creates testing flexibility. It also raises claim-construction issues concerning:

The dissolution medium.
The number of tested units.
The applicable USP acceptance criteria.
Whether the claim requires 85% dissolution for each unit or an average.
Whether the test is performed on the caplet before encapsulation or on the finished capsule.

USP <711> addresses dissolution testing but does not independently resolve every product-specific testing question. [2]

Which claims are strongest commercially?

Claims 10 and 11 are likely the most commercially targeted because they recite complete dosage configurations independently rather than depending on claim 1.

Claim	Commercial relevance	Main vulnerability
1	Broadest product combination	Must prove every limitation, including “optimizes”
3	Preferred density range	Vulnerable to measurement methodology
4	#0 capsule configuration	Requires capsule-fit relationship
10	667 mg/#0 capsule product	Strong product read-on if marketed configuration matches
11	Approximately 333.5 mg/#2 capsule product	Numerical inconsistency and capsule-fit proof
12	Treatment method	Requires administration of the claimed formulation
13	667 mg/#0 method configuration	Narrow and commercially specific
15	Smaller-dose method configuration	Contains apparent amount discrepancy

Claims 2, 5, 6, 8, 9, 13, and 15 add dosage or hydration details but are dependent or highly narrow. Their practical value is strongest where a product uses the exact capsule and dosage architecture.

Are there drafting errors in the supplied claims?

Yes. Claims 12, 13, and 15 contain apparent typographical errors:

“hulk density” instead of “bulk density.”
“bilk density” instead of “bulk density.”
“anhydrous basics” instead of “anhydrous basis.”
Claim 15 recites 335.5 mg, while claim 8 recites 333.3 mg and the surrounding formulation appears to target approximately one-half of 667 mg.

A court could construe obvious typographical errors based on the patent specification and prosecution record. The errors do not automatically invalidate the claims. They can, however, create disputes over indefiniteness, correction, written description, or the scope of the claimed dosage.

What was the patent’s legal status and expiration date?

U.S. Patent 6,576,665 issued on June 10, 2003. The patent term was tied to the nonprovisional application filing date rather than the earlier development history. The patent expired in January 2021, approximately 20 years after the relevant nonprovisional filing date, subject to any applicable patent-term adjustment recorded by the USPTO. [1][3]

The patent is therefore expired and cannot support a current U.S. injunction against a generic calcium acetate product.

Event	Date or status
U.S. application filing	January 2001
Patent issue	June 10, 2003
Historical product relevance	PhosLo and calcium acetate phosphate-binder capsules
Patent expiration	January 2021
Current enforceability	Expired
Current Paragraph IV risk	None under this patent
Current biosimilar relevance	None

The patent’s expiration also removes the practical significance of its formulation-specific claim limitations for present-day U.S. entry. A manufacturer may still need to satisfy FDA quality, labeling, bioequivalence, and manufacturing requirements, but those requirements are separate from patent exclusivity.

What was the Orange Book status of U.S. Patent 6,576,665?

The patent was associated with the PhosLo calcium acetate product franchise and was relevant to FDA-listed patent litigation and abbreviated new drug application activity. The Orange Book identifies patents submitted by NDA holders for approved drug products, including use patents and certain formulation patents. [4]

The patent’s Orange Book relevance was historical. Because it expired in 2021, it no longer creates a live Orange Book patent obstacle for an ANDA applicant.

A Paragraph IV certification would historically have alleged that the patent was invalid, unenforceable, or not infringed. A timely patent-infringement action following a Paragraph IV notice could have triggered the 30-month stay under the Hatch-Waxman framework. [5] That mechanism no longer provides a current entry delay based on the expired patent.

Which companies challenged or competed against the PhosLo patent?

The commercial challenge came from generic calcium acetate manufacturers filing ANDAs for products equivalent or therapeutically substitutable to PhosLo. Public litigation records identify disputes involving Nabi Biopharmaceuticals and Roxane Laboratories concerning the patent and generic calcium acetate products.

The commercial competitive field included:

Nabi Biopharmaceuticals, associated with the PhosLo franchise.
Roxane Laboratories, a generic pharmaceutical company.
Other ANDA applicants marketing calcium acetate capsules or tablets after the relevant exclusivity and patent barriers declined.

The central generic strategy was to offer calcium acetate in a formulation that met FDA equivalence requirements while contesting or avoiding the patent’s caplet, density, capsule, and dissolution limitations.

Historical litigation did not create a lasting proprietary barrier. The patent’s expiration converted the issue from patent clearance to ordinary product development and regulatory compliance.

What patent landscape surrounds calcium acetate phosphate binders?

Calcium acetate is an old active pharmaceutical ingredient. The important patent distinction is between the active ingredient and the dosage-form engineering.

Technology area	Patent strength today	Explanation
Calcium acetate molecule	Low	No current composition-of-matter exclusivity
Phosphate binding use	Low	Broad medical use was known before the patent
Compressed caplet in capsule	Historical, now expired	Core subject of US 6,576,665
Bulk-density-controlled material	Historical, now expired	Numerical formulation limitation
Rapid dissolution	Historical, now expired	Performance limitation
Manufacturing process	Product-dependent	May involve separate patents or trade secrets
New delivery system	Potentially patentable	Requires a genuinely novel formulation or device
Calcium acetate combination product	Potentially patentable	Depends on novelty and nonobviousness
Biologic or biosimilar protection	Not applicable	Calcium acetate is a small-molecule drug

The main residual competitive advantages are manufacturing scale, raw-material control, tablet compression know-how, dissolution consistency, packaging, and FDA-approved labeling. Those factors may affect cost and substitution but are not equivalent to patent exclusivity.

How does calcium acetate compare with competing phosphate binders?

Calcium acetate competes with sevelamer, lanthanum carbonate, ferric citrate, and sucroferric oxyhydroxide.

Product class	Active ingredient	Patent profile	Key commercial distinction
Calcium acetate	Calcium acetate	Mature and largely off-patent	Low-cost calcium-based binder
Sevelamer	Sevelamer carbonate or hydrochloride	Historically extensive formulation and method patents	Non-calcium polymer binder
Lanthanum carbonate	Lanthanum carbonate	Historical composition and formulation protection	Chewable-tablet positioning
Ferric citrate	Ferric citrate	More recent formulation and method patents	Iron-containing phosphate binder
Sucroferric oxyhydroxide	Sucroferric oxyhydroxide	Product-specific patent estate	Iron-based chewable binder

Calcium acetate has the weakest current patent protection among the major phosphate-binder products because its core formulation patents have expired. Its competitive position depends mainly on price, availability, tolerability, calcium-load considerations, and prescribing practice.

What generic launch risks exist after patent expiration?

After January 2021, the principal launch risks were regulatory and commercial rather than patent-based.

Regulatory risks

An ANDA applicant must demonstrate pharmaceutical equivalence and bioequivalence or satisfy the FDA’s applicable waiver or product-specific requirements. The applicant must also comply with current good manufacturing practice, stability, dissolution, content uniformity, and labeling requirements. [6]

Formulation risks

A calcium acetate caplet must maintain:

Dose uniformity.
Mechanical strength.
Capsule fit.
Rapid and reproducible dissolution.
Stability under storage conditions.
Acceptable handling during encapsulation and packaging.

Commercial risks

Calcium acetate is a commodity-like generic market. Entry can produce rapid price erosion, especially where multiple manufacturers receive approval. The lack of active patent protection increases competition but reduces the value of licensing the expired patent.

Litigation risks

No current infringement action can be based on an expired patent. A manufacturer could still face litigation over a different, later-expiring formulation patent, trade dress, labeling, trademarks, or manufacturing technology. Those risks are separate from U.S. Patent 6,576,665.

Is a license to U.S. Patent 6,576,665 still commercially valuable?

No ordinary patent license is required for current U.S. practice because the patent has expired. Historical licensing or settlement arrangements may have governed launch timing before expiration, but they do not extend the patent term.

A transaction involving the old patent would have value only as part of a historical dispute, portfolio review, chain-of-title investigation, or litigation archive. It would not provide current exclusionary rights over calcium acetate capsules.

How strong was the patent estate?

The estate was commercially meaningful during its term but technically narrow.

Strength factor	Assessment
Active ingredient coverage	Weak
Product-specific coverage	Moderate
Ease of designing around	Moderate to high
Reliance on measurable parameters	High
Claim breadth	Limited by cumulative limitations
Litigation leverage before expiration	Material
Current exclusionary value	None
Manufacturing barrier	Low to moderate
Biosimilar relevance	None

The strongest historical position was against a product that copied the same 667 mg calcium acetate caplet, #0 capsule, density range, and rapid-dissolution profile. The patent was less effective against tablets, powder-filled capsules, different capsule sizes, altered density, or formulations outside the dissolution limitation.

Key Takeaways

U.S. Patent 6,576,665 covered a specific calcium acetate caplet-in-capsule formulation, not calcium acetate generally.
The core limitations were bulk density, capsule fit, dosage amount, and rapid dissolution.
Claims 10 and 11 were the most commercially specific independent product claims.
Claims 12 through 15 covered administration of the claimed formulation rather than phosphate binding with calcium acetate generally.
The patent expired in January 2021.
Its Orange Book and Paragraph IV significance is historical.
Calcium acetate is not subject to current U.S. composition-of-matter or biosimilar exclusivity.
Current generic-entry risk is driven by FDA requirements, manufacturing capability, pricing, and any unrelated later patents.
The patent’s residual business value is archival or litigation-related, not exclusionary.

FAQs

Does U.S. Patent 6,576,665 cover all PhosLo products?

No. It covers products meeting the specified density, caplet, capsule, dosage, and dissolution limitations. Other PhosLo dosage forms may not satisfy every limitation.

Can a generic manufacturer sell calcium acetate capsules after the patent expired?

Yes, provided the product satisfies applicable FDA requirements and does not infringe another unexpired patent.

Does the patent cover sevelamer or ferric citrate?

No. The claims are limited to calcium acetate compositions and methods.

Is a Paragraph IV certification still required for this patent?

No current Paragraph IV challenge is required for an expired patent. The certification framework applies to listed patents that remain relevant to ANDA approval.

Could the capsule-size limitations support infringement of a tablet product?

Generally, no literal infringement would exist if the product is not a compressed caplet fitted inside the claimed capsule. The analysis could differ only if a valid equivalents theory applied, which would depend on the specific product and litigation record.

References

U.S. Patent No. 6,576,665. (2003). Calcium acetate compositions and methods of use. United States Patent and Trademark Office.
United States Pharmacopeia. (2023). General chapter <711>: Dissolution. United States Pharmacopeial Convention.
United States Patent and Trademark Office. (2024). Patent term calculator and patent term adjustment guidance.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
21 U.S.C. § 355(j). (2024). Abbreviated applications for new drugs.
U.S. Food and Drug Administration. (2024). ANDA submissions: Content and format.

Details for Patent: 6,576,665

Summary for Patent: 6,576,665