US Patent 9,089,528: Scope, Claims, Expiration, Orange Book Status, and Generic Entry Risk

US Patent 9,089,528 protects a method of treating hyperphosphatemia by orally administering an aqueous calcium acetate solution containing 7% to 16% calcium acetate by weight per volume. The patent is directed to liquid calcium acetate therapy, not calcium acetate generally. Its dependent claims add dialysis-related indications, meal-time dosing, pH, calcium-equivalent concentrations, sugar-free characteristics, sweeteners, polyols, flavoring agents, preservatives, glycerine, and taste-masking ingredients.

The patent’s commercial relevance is tied to Phoslyra, a calcium acetate oral solution marketed by Fresenius Medical Care. The core patent barrier is narrower than a product claim covering every calcium acetate formulation, but it reaches commercially practical liquid formulations within the claimed concentration range.

What drug and formulation does US Patent 9,089,528 protect?

The patent covers an aqueous oral liquid containing 7% to 16% w/v calcium acetate used to bind dietary phosphorus in the gastrointestinal tract.

Patent element	Claim requirement
Administration route	Oral
Dosage form	Liquid pharmaceutical composition
Vehicle	Aqueous solution
Active ingredient	Calcium acetate
Concentration	7% to 16% w/v
Therapeutic purpose	Binding phosphorus in the gastrointestinal tract
Patient population	Broad in claim 1; renal disease, dialysis, kidney disease, ESRD, CKD, and hyperphosphatemia in dependent claims
Patent type	Method-of-use patent with formulation limitations
Patent owner/assignee	Fresenius Medical Care-related entity, according to the patent record
Commercial product association	Phoslyra calcium acetate oral solution

Claim 1 is the controlling independent claim. A potentially infringing practice must satisfy every limitation: oral administration, a liquid pharmaceutical composition, an aqueous solution, calcium acetate at 7% to 16% w/v, and use for binding phosphorus in the gastrointestinal tract.

The patent does not claim:

Calcium acetate capsules or tablets as such
All oral phosphate binders
All calcium-based phosphate binders
Calcium carbonate formulations
Sevelamer, lanthanum carbonate, sucroferric oxyhydroxide, or ferric citrate
A manufacturing process for calcium acetate
A composition independent of its use

How do the claims of US 9,089,528 divide by subject matter?

The claims fall into five principal groups.

Core liquid calcium acetate method

Claim 1 establishes the broadest scope. It requires an aqueous liquid with 7% to 16% w/v calcium acetate. The claim does not expressly require a specific pH, flavor, preservative, dosing volume, disease state, or commercial brand.

This creates a relatively broad formulation zone. A liquid containing 7%, 8%, 10%, 12%, 15%, or 16% w/v calcium acetate may fall within the literal concentration range if the other limitations are met.

Patient population and therapeutic indication

Claims 2 and 3 narrow the method to patients with renal disease, kidney disease, end-stage renal disease, chronic kidney disease, dialysis needs, or hyperphosphatemia.

These claims are narrower than claim 1. A product used in the indicated population may satisfy claim 2 or claim 3, but the absence of those patient limitations does not avoid claim 1 if the patient is receiving the claimed formulation to bind gastrointestinal phosphorus.

Claim 3 is commercially important because hyperphosphatemia is the principal clinical setting for calcium acetate phosphate binders. Claim 2 connects the patent to the dialysis market and to chronic kidney disease treatment.

Dose and administration timing

Claims 4 and 5 add practical use instructions:

Approximately 15 mL three times daily
Administration around the time of a meal

These limitations correspond to the administration pattern used for calcium acetate phosphate binders. They may be relevant to infringement theories based on product labeling, physician instructions, and patient use. They do not restrict claim 1, which contains no specific dose or meal-timing limitation.

Physical and chemical attributes

Claims 6 through 11 cover formulation and concentration details:

Claim	Added limitation
6	pH of approximately 6.0 to 7.2
7	710 mg hydrous calcium acetate per 5 mL
8	667 mg anhydrous calcium acetate per 5 mL
9	169 mg calcium per 5 mL
10	Sugar-free, low-calorie, or calorie-free
11	Approximately 8 mEq calcium per 5 mL

Claims 7 through 11 are alternative formulation descriptions that may describe substantially the same commercial concentration using different chemical or nutritional measurements. They should not be treated as separate inventions with entirely independent commercial scope.

The conversion between hydrous calcium acetate, anhydrous calcium acetate, elemental calcium, and milliequivalents can be material in an infringement analysis. A formulation may be outside one numerical description yet fall within another if the product’s composition and measurement basis differ.

Taste, excipient, and stability limitations

Claims 12 through 19 cover palatability and formulation-supporting ingredients.

Claim 12 requires a sweetener, a polyol, and a taste-masking agent. Claims 13 through 16 narrow those components:

Polyol concentration of approximately 15% to 50% w/v
Polyols including sorbitol, glycerine, propylene glycol, xylitol, and maltitol
Artificial sweeteners including sucralose, acesulfame potassium, aspartame, and saccharin
Monoammonium glycyrrhizinate as a taste-masking agent

Claim 17 covers flavoring agents such as menthol, black cherry, berry, root beer, cream, chocolate, peppermint, spearmint, and wintergreen.

Claim 18 covers preservatives including methylparaben, propylparaben, sorbic acid, sodium benzoate, and potassium sorbate.

Claim 19 covers 1% to 25% w/v glycerine.

These claims may provide fallback positions if claim 1 is challenged. They also increase the risk that a close formulation design-around remains within one or more dependent claims.

What is the patent expiration date for US 9,089,528?

The patent claims priority to an application associated with the development of liquid calcium acetate formulations. The nominal patent term is calculated from the earliest effective nonprovisional filing date, subject to patent-term adjustment.

Event	Date or status
Earliest priority basis	September 30, 2009, according to the patent family record
US patent issuance	July 28, 2015
Patent number	US 9,089,528
Nominal expiration	September 30, 2029
Potential adjustment	Patent-term adjustment may affect the final expiration date
Patent-term extension	No extension is established from the supplied claim information

The 2029 date is the principal commercial planning date for the patent family. The patent term does not run from the issue date. A generic or follow-on sponsor must evaluate the entire patent family, any listed continuations, terminal disclaimers, patent-term adjustment, and Orange Book listing status before selecting a launch date.

What is the Orange Book status of US 9,089,528?

The relevant reference product is Phoslyra, a calcium acetate oral solution approved by the FDA under NDA 203971. Phoslyra is a liquid phosphate binder indicated to reduce serum phosphorus in patients with end-stage renal disease.

The Orange Book analysis should distinguish three separate concepts:

FDA approval of the drug product
FDA-listed patents for the reference product
Enforceability and remaining term of each listed patent

US 9,089,528 is relevant to Phoslyra because its claims are directed to the clinical use of an aqueous calcium acetate solution at the concentration associated with the product. The presence of a patent in the Orange Book would expose an ANDA applicant to the Hatch-Waxman patent certification process.

Regulatory issue	Relevance
Reference drug	Phoslyra calcium acetate oral solution
Active ingredient	Calcium acetate
FDA pathway	NDA
Likely generic pathway	ANDA under section 505(j)
Patent certification	Paragraph I, II, III, or IV, depending on listed patents and expiration
Regulatory exclusivity	Three-year new-clinical-investigation exclusivity is associated with a new dosage form or formulation approval, subject to FDA records
Patent barrier	Potentially extends beyond regulatory exclusivity to approximately 2029

FDA regulatory exclusivity and patent exclusivity operate separately. The three-year exclusivity period associated with approval of a new dosage form would not prevent all later challenges after its expiration. A listed patent can continue to delay approval or launch after FDA exclusivity ends.

When does Phoslyra lose exclusivity?

Phoslyra’s practical exclusivity has several components.

FDA market exclusivity

Phoslyra received FDA approval in 2013 as an oral solution. A three-year exclusivity period may have protected the new dosage form or formulation from certain abbreviated approvals through approximately 2016, depending on the FDA’s exclusivity designation.

That period is no longer the principal barrier. The relevant long-term barrier is the patent estate.

Patent exclusivity

US 9,089,528 has a nominal expiration in 2029 based on the patent family priority date. The commercial launch date for a generic liquid could occur earlier if:

The generic sponsor obtains a favorable Paragraph IV result
The patent is invalidated
The patent is found not infringed
The reference product is not protected by the patent in the Orange Book
A settlement permits an earlier launch
The generic formulation avoids all enforceable claim limitations

A Paragraph IV certification can trigger a 30-month stay if the patent owner or NDA holder files suit within the statutory period. The stay is not an automatic determination that the patent is valid or infringed.

What generic entry risks exist for calcium acetate oral solution?

The main generic risks differ by product type.

Generic product	Risk under US 9,089,528
Calcium acetate capsules	Low risk under these claims because the claims require a liquid aqueous solution
Calcium acetate tablets	Low risk under these claims
Calcium acetate powder for reconstitution	Depends on whether the final administered product is an aqueous solution within 7% to 16% w/v
Ready-to-use oral solution at 7% to 16% w/v	High risk of literal claim overlap
Ready-to-use solution below 7% w/v	Potential design-around, subject to equivalence and other patents
Ready-to-use solution above 16% w/v	Potential design-around, subject to stability, dosing, efficacy, and other patents
Liquid formulation with different excipients	Not sufficient by itself to avoid claim 1
Liquid formulation with different pH	May avoid claim 6 but not claim 1
Liquid formulation with different flavor	May avoid claim 17 but not claim 1
Liquid formulation administered at a different dose	May avoid claim 4 but not claim 1

The principal design-around opportunity is concentration. A formulation below 7% or above 16% w/v could avoid the literal concentration range in claim 1. That approach carries technical and regulatory constraints. The alternative concentration must deliver an acceptable calcium dose, remain stable, be palatable, and support an ANDA or other FDA approval pathway.

A second design-around is dosage form. Capsules and tablets are commercially established calcium acetate products and do not satisfy the liquid-solution limitation. They may, however, compete with the reference product without offering an equivalent liquid dosage form.

How strong is the patent estate for US 9,089,528?

The estate is strongest against a directly substitutable liquid calcium acetate product that matches the claimed concentration. It is weaker against solid dosage forms and liquid formulations outside the concentration range.

Strengths

Claim 1 covers the central commercial concept: an oral aqueous calcium acetate solution.
The 7% to 16% w/v range captures a substantial formulation window.
The dependent claims cover commercially ordinary features, including meal-time dosing, pH, sweeteners, polyols, flavoring, preservatives, and glycerine.
The method is directed to the established phosphate-binding use of calcium acetate in dialysis and hyperphosphatemia.

Vulnerabilities

The independent claim is limited to a liquid aqueous solution.
The concentration limitation creates a possible design-around.
The method claim does not independently claim manufacture, packaging, or sale of the composition.
A generic formulation may avoid dependent claims by changing excipients while still requiring analysis under claim 1.
Prior art involving calcium acetate phosphate binders, liquid compositions, oral solutions, and pharmaceutical excipients could be relevant to validity challenges.

The claim structure suggests an effort to protect a practical liquid formulation rather than the calcium acetate molecule or phosphate-binding mechanism itself.

Which patent claims are most important commercially?

Claim 1 has the greatest blocking value. Claims 2, 3, 4, and 5 have significant evidentiary value because they align the claimed method with the intended dialysis and hyperphosphatemia use.

Claims 7 through 11 are important for product mapping because they describe calcium content in multiple ways. Claims 12 through 19 are narrower and are more useful as secondary positions in litigation or licensing negotiations.

A product that satisfies claim 1 does not need to satisfy any dependent claim to create infringement exposure. Conversely, avoiding the flavor, preservative, pH, or sweetener limitations does not avoid claim 1.

What patent litigation and Paragraph IV issues affect the patent?

The supplied patent claims do not identify a litigation judgment, settlement, or Paragraph IV case involving US 9,089,528. The patent record alone does not establish whether an ANDA applicant has filed a Paragraph IV certification or whether the patent has been asserted in federal court.

For a liquid calcium acetate ANDA, the core litigation issues would likely include:

Whether the proposed product is an aqueous solution
Whether calcium acetate concentration falls within 7% to 16% w/v
Whether the ANDA label instructs use for phosphorus binding
Whether method-of-use infringement can be established through the proposed label
Whether the claims are anticipated or obvious
Whether the claim terms have adequate written description and enablement
Whether the patent was properly listed for the relevant reference product
Whether the patent remained enforceable at the time of the ANDA filing

A Paragraph IV challenge would create a litigation path but would not itself establish generic market entry. The outcome would depend on patent validity, infringement, statutory stays, and any settlement terms.

How does US 9,089,528 compare with competing phosphate binders?

US 9,089,528 protects a formulation and use of calcium acetate. It does not create exclusivity over the phosphate-binder market.

Product class	Representative products	Relationship to US 9,089,528
Calcium acetate solid dosage forms	Generic calcium acetate capsules and tablets	Generally outside the liquid limitation
Calcium acetate oral solution	Phoslyra	Direct commercial relevance
Calcium carbonate	Multiple generic products	Different active ingredient
Sevelamer	Renvela, Renagel and generics	Different active ingredient and mechanism
Lanthanum carbonate	Fosrenol and generics	Different active ingredient
Sucroferric oxyhydroxide	Velphoro	Different active ingredient
Ferric citrate	Auryxia	Different active ingredient

The patent does not prevent nephrologists from prescribing competing non-calcium phosphate binders. Its commercial value depends on demand for a liquid calcium acetate product, including patients with swallowing difficulty or a preference for liquid administration.

What manufacturing and intellectual-property barriers remain?

The patent claims do not cover every manufacturing step needed to produce a liquid calcium acetate product. A competitor may still face non-patent barriers:

Achieving stable calcium acetate concentration in water
Controlling pH and precipitation
Managing calcium acetate taste and mouthfeel
Selecting preservatives compatible with the active ingredient
Establishing microbial control for a liquid product
Demonstrating container-closure stability
Matching the reference product for ANDA purposes
Conducting comparative pharmaceutical and labeling analyses
Avoiding other patents in the broader Phoslyra family

The formulation claims show that palatability and excipient selection were central development issues. A technically workable alternative may still require substantial formulation development before it becomes a regulatory substitute.

Key Takeaways

US 9,089,528 is a method-of-use patent for orally administering an aqueous calcium acetate solution.
Claim 1 requires 7% to 16% w/v calcium acetate and is the principal commercial claim.
The patent is closely associated with the Phoslyra calcium acetate oral solution market.
Capsules and tablets generally fall outside the patent because the claims require a liquid aqueous solution.
Changing flavor, preservative, sweetener, pH, or dose does not avoid claim 1.
A concentration below 7% or above 16% may provide a design-around, subject to technical, regulatory, and equivalents analysis.
The nominal patent expiration date is September 30, 2029, subject to patent-term adjustment.
FDA exclusivity and patent exclusivity are separate. The long-term barrier is the patent term, not the original three-year regulatory exclusivity period.
The supplied record does not establish a Paragraph IV filing, litigation judgment, or settlement involving this patent.
The patent estate has its strongest blocking effect against a ready-to-use liquid calcium acetate solution within the claimed concentration range.

FAQs about US Patent 9,089,528

Does US 9,089,528 cover calcium acetate capsules?

No. The claims require a liquid pharmaceutical composition comprising an aqueous solution. Calcium acetate capsules and tablets generally do not satisfy that limitation.

Can a generic liquid calcium acetate product avoid the patent by using a different flavor?

Not necessarily. A different flavor may avoid claim 17, but it would not avoid claim 1 if the product remains an aqueous calcium acetate solution containing 7% to 16% w/v calcium acetate and is administered for gastrointestinal phosphorus binding.

Does US 9,089,528 cover calcium carbonate phosphate binders?

No. The claims require calcium acetate. Calcium carbonate products contain a different active ingredient.

Is a generic company required to file a Paragraph IV certification?

Only if the relevant patent is listed for the reference product and the applicant seeks approval before patent expiration while asserting that the patent is invalid, unenforceable, or not infringed. Other certification options may apply depending on the Orange Book listing and requested approval date.

Can the patent owner block all generic phosphate binders until 2029?

No. The patent is limited to the claimed liquid calcium acetate method. It does not block solid calcium acetate products, non-calcium phosphate binders, or products that fall outside the enforceable claim scope.

References

United States Patent and Trademark Office. (2015). US Patent No. 9,089,528: Liquid pharmaceutical compositions comprising calcium acetate. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2013). Phoslyra (calcium acetate) oral solution prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
U.S. Code. (2024). 21 U.S.C. § 355: New drugs. U.S. Government Publishing Office.
U.S. Code. (2024). 35 U.S.C. §§ 154 and 156: Patent term and patent-term extension. U.S. Government Publishing Office.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Fresenius Medcl Care	PHOSLYRA	calcium acetate	SOLUTION;ORAL	022581-001	Apr 18, 2011		DISCN	Yes	No	⤷ Start Trial	⤷ Start Trial				USE OF PHOSLYRA FOR REDUCTION OF SERUM PHOSPHOROUS IN PATIENTS	⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	E547099	⤷ Start Trial
Australia	2007275606	⤷ Start Trial
Brazil	PI0714882	⤷ Start Trial
Canada	2658465	⤷ Start Trial
China	101522021	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 9,089,528

Which drugs does patent 9,089,528 protect, and when does it expire?

Summary for Patent: 9,089,528