United States Patent 8,591,938: What Is Claimed and Where It Sits in the U.S. Landscape
US Drug Patent 8,591,938 covers an oral liquid calcium acetate formulation and a use method for binding phosphorus in the gastrointestinal (GI) tract. The claims are drafted around a narrow composition architecture: high-concentration calcium acetate in water plus a defined sweetener/polyol package plus monoammonium glycyrrhizinate taste masking, with optional excipients for stability, pH control, and palatability, and with dosing and GI-relevant use assertions.
1. What does the patent claim (composition and use)?
A. Core composition claim (Claim 1)
Claim 1 is an oral dosage form defined by a liquid pharmaceutical composition that is an aqueous solution containing four required functional components:
- Calcium acetate: 7-16% (w/v)
- Artificial sweetener selected from: sucralose, acesulfame potassium, aspartame, saccharin
- Polyol selected from: sorbitol, glycerine, propylene glycol, xylitol, maltitol, and combinations
- Taste masking agent: monoammonium glycyrrhizinate
The claim language ties the invention to a specific taste-management strategy (monoammonium glycyrrhizinate) and to a defined palatability matrix (sweetener + polyol).
B. Concentration guardrails (dependent claims)
The claim set then constrains preferred quantitative ranges and exemplifies two specific embodiments:
Calcium acetate
- Claim 2: 12-16% (w/v)
- Claim 3: about 14% (w/v)
Total polyol
Sorbitol-specific polyol embodiments
- Claim 5: 15-40% (w/v) sorbitol
- Claim 6: about 21% (w/v) sorbitol
Maltitol-specific polyol embodiments
- Claim 7: 15-25% (w/v) maltitol
- Claim 8: about 20% (w/v) maltitol
Glycerine within the polyol system
- Claim 9: 1-25% (w/v) glycerine
- Claim 10: about 5% (w/v) glycerine
Artificial sweetener narrowing
- Claim 11: sweetener is sucralose or saccharin
- Claim 12: about 0.35% (w/v) sucralose or about 0.15% (w/v) saccharin
pH
C. Optional excipients broaden real-world coverage
The independent composition claim is expanded by optional dependent claims that typically appear in formulation patents for acceptability and shelf-life:
- Flavoring agent (Claims 13-17): includes berry, root beer, cream, chocolate, peppermint, spearmint, wintergreen, and in Claim 16 black cherry, with Claim 17 specifying artificial black cherry
- Menthol flavor (Claim 15 and embedded in Claim 24)
- Preservative (Claims 18-20): methylparaben, propylparaben, sorbic acid, sodium benzoate, potassium sorbate; Claim 20 specifies methylparaben
- PVP inclusion (Claim 21; explicitly in Claim 24/25)
- Propylene glycol as part of polyol (Claim 22)
D. Two explicit “formula exemplars” (Claims 24 and 25)
Claim 24 (sorbitol version) and Claim 25 (maltitol version) are full-portfolio composition definitions with numeric values:
Claim 24 (sorbitol embodiment)
- Sorbitol: 21% (w/v)
- Calcium acetate: 14% (w/v)
- Glycerine: 5% (w/v)
- Propylene glycol: 2% (w/v)
- Monoammonium glycyrrhizinate: 0.25% (w/v)
- Sucralose: 0.35% (w/v)
- PVP: 0.75% (w/v)
- Methylparaben: 0.2% (w/v)
- Artificial black cherry flavor: 0.2% (w/v)
- Menthol flavor: 0.2% (w/v)
Claim 25 (maltitol embodiment)
- Maltitol: 20% (w/v)
- Calcium acetate: 14% (w/v)
- Glycerine: 5% (w/v)
- Propylene glycol: 2% (w/v)
- Monoammonium glycyrrhizinate: 0.25% (w/v)
- Sucralose: 0.35% (w/v)
- PVP: 0.75% (w/v)
- Methylparaben: 0.2% (w/v)
- Artificial black cherry flavor: 0.2% (w/v)
- Menthol flavor: 0.2% (w/v)
These exemplars matter because they anchor the claim to a manufacturable formulation that competitors can inadvertently map onto.
E. Dose-per-volume definitions (Claims 26-28)
The formulation is also pegged to calcium acetate / calcium content in 5 mL:
- Claim 26: ~710 mg hydrous calcium acetate per 5 mL
- Claim 27: ~667 mg anhydrous calcium acetate per 5 mL
- Claim 28: ~169 mg calcium per 5 mL
This turns the patent into a product-by-spec target for label-level equivalents.
F. “Diet positioning” language (Claims 29-31)
Claims 29-31 specify that the composition may be:
- sugar-free (Claim 29)
- low-calorie (Claim 30)
- calorie-free (Claim 31)
These claims read like regulatory-friendly descriptors, but they also increase the chance of overlap with marketed “reformulated” phosphate binders aimed at CKD/diet-constrained populations.
G. Calcium equivalence (Claim 32)
- Claim 32: composition comprises about 8 milliequivalents of calcium
This is another anchor for functional equivalence that can be used in infringement mapping.
2. What does the patent claim for methods of use? (Claims 33-68)
The second half of the claim set is a method for binding phosphorus via oral administration of the same constrained composition.
A. Method claim (Claim 33)
Claim 33 recites:
- administering to an individual
- an oral liquid pharmaceutical composition that includes:
- 7-16% (w/v) calcium acetate
- sweetener selected from sucralose/acesulfame potassium/aspartame/saccharin
- polyol selected from sorbitol/glycerine/propylene glycol/xylitol/maltitol (and combinations)
- taste masking agent monoammonium glycyrrhizinate
B. Clinical target (Claim 34 and 66)
- Claim 34: individual is in need of dialysis and/or has disorders including renal disease / kidney disease / end stage renal disease / chronic kidney disease
- Claim 66: method for the individual is suffering from hyperphosphatemia
These claims do not require a particular CKD staging label; they rely on functional therapeutic context.
C. Method formulation concentration constraints (Claims 35-45, 37-43)
The method claims parallel the composition constraints:
- calcium acetate: 12-16% (Claim 35), about 14% (Claim 36)
- total polyol: 15-50% (Claim 37)
- sorbitol: 15-40% (Claim 38) and about 21% (Claim 39)
- maltitol: 15-25% (Claim 40) and about 20% (Claim 41)
- glycerine: 1-25% (Claim 42) and about 5% (Claim 43)
- sweetener: sucralose or saccharin with 0.35% sucralose or 0.15% saccharin (Claim 44-45)
D. Taste and stability add-ons persist in method claims
Flavor and preservative options reappear:
- flavor agents including menthol and black cherry (Claims 46-50)
- preservatives including methylparaben (Claims 51-53)
- PVP included (Claim 54)
- propylene glycol included (Claim 55)
- pH range (Claim 56)
E. Method exemplars mirror Claims 24-25
- Claim 57: the full sorbitol exemplar
- Claim 58: the full maltitol exemplar
F. Dosing directions (Claims 67-68)
- Claim 67: administer about 1 tablespoon (15 mL) three times per day
- Claim 68: administer around the time of ingestion of a meal
These dosing claims can be a friction point for generic or reformulated entrants who try to keep composition design-around but use similar dosing regimens.
3. What is the infringement “core” and where are design-arounds most plausible?
A. The invention’s center of gravity
The binding constraint in both composition and method is the conjunction of:
- calcium acetate concentration 7-16% (w/v)
- monoammonium glycyrrhizinate as taste masking
- a specified sweetener class plus a polyol class
- with optional pH and excipient choices that appear in many aqueous formulations
In infringement mapping, the most decisive elements are:
- monoammonium glycyrrhizinate presence
- calcium acetate level within 7-16% (w/v)
- sweetener and polyol selection from the claimed sets
- (second-tier) whether they track the exemplar concentrations (Claims 24/25) or dose-per-5 mL calcium statements (Claims 26-28)
B. Likely “hard” design-arounds
Because the claim is a closed set of alternatives for sweetener/polyol but includes multiple members within each set, the primary design-around vectors tend to be structural:
- Remove monoammonium glycyrrhizinate (not just change concentration, but switch taste masking agent type)
- Move calcium acetate out of 7-16% (w/v) range for the aqueous liquid solution
- Use a sweetener or polyol outside the enumerated lists
- Note: the claims allow “combinations thereof,” so partial overlap does not escape if the remaining ingredients still fall within the enumerated sets.
C. Likely “soft” design-arounds
These may avoid the dependent claim embodiments but still land in the independent claim:
- Adjust flavor system (the dependent claims list flavors; Claim 1 only requires monoammonium glycyrrhizinate as taste masking, plus sweetener and polyol)
- Adjust PVP/methylparaben, because those are not required by Claim 1
- Adjust pH slightly only if it is still within Claim 1’s broader scope (Claim 1 does not state pH; Claim 23 adds a dependent pH restriction)
4. Claim strategy: what the dependent claims add to enforcement leverage
The dependent claim set does four things that matter commercially:
-
Quantitative tightening
It creates multiple “infringement ladders” where a challenger can meet one range without matching another (e.g., calcium acetate 12-16% vs 7-16%).
-
Exemplar locking
Claims 24 and 25 define a near-exact composition that is easier to map against an actual product formulation.
-
Dose specification
Claims 26-28 convert w/v concentrations into per-volume mass/equivalence, which is useful for product labeling, lot testing, and forensic comparison.
-
Therapeutic method coverage
Claims 33-68 extend coverage to labeled indications and administration practices for CKD/hyperphosphatemia patients.
5. Patent landscape implications for U.S. competitors (practical landscape read)
A. Landscape shape: formulation patent, not API monopoly
The patent is about a formulation architecture for calcium acetate and a taste masking approach, not about novel calcium acetate salts or new calcium acetate chemistry. That typically means:
- the market’s main competitive differentiators are taste, adherence, dosing convenience, and manufacturability
- infringement disputes often turn on ingredient-by-ingredient compliance and exact w/v calcium acetate ranges
B. High-risk overlap profile
Competitors reformulating aqueous calcium acetate phosphate binders must avoid a “triple match”:
- calcium acetate in the 7-16% (w/v) window
- at least one claimed artificial sweetener
- at least one claimed polyol
- plus monoammonium glycyrrhizinate as taste masking
If all four are present, the independent claim is met even if flavor/preservatives differ.
C. Portfolio friction for generics or licensees
If a generic seeks to launch an oral liquid calcium acetate with the same taste masking logic and comparable calcium concentration, it may face:
- direct composition infringement risk (Claim 1)
- direct method infringement risk (Claim 33), depending on label and administration directions (Claims 67-68)
Key Takeaways
- The patent’s enforceable core is the combination of aqueous calcium acetate (7-16% w/v) plus monoammonium glycyrrhizinate taste masking plus claimed sweetener and polyol alternatives.
- Claims 24-25 and 26-28 create “product-spec” checkpoints that are easy to compare against a commercial formulation.
- Method claims track CKD/dialysis/hyperphosphatemia use and include administration timing and dosing volume frequency.
- Design-arounds most plausibly require changing taste masking agent away from monoammonium glycyrrhizinate and/or moving calcium acetate out of the 7-16% (w/v) band, not just changing flavor or excipient grade.
FAQs
1. Does the patent require specific flavoring agents?
No. Flavoring agents appear in dependent claims, while Claim 1 only requires monoammonium glycyrrhizinate plus the sweetener and polyol selections.
2. What is the tightest calcium acetate constraint in the set?
The narrowest dependent calcium acetate range is 12-16% (w/v) (Claim 2), with a preferred specific point at about 14% (w/v) (Claim 3 and echoed in exemplars).
3. Which ingredient is most central for taste in Claim 1?
Monoammonium glycyrrhizinate is required in Claim 1 and is repeated throughout the method claims.
4. Do the method claims require dialysis specifically?
No. Claim 34 includes dialysis and/or renal disease categories, and Claim 66 explicitly covers hyperphosphatemia.
5. Can a product avoid infringement by changing only preservatives or PVP?
Preservatives and PVP are present in dependent claims and exemplars, but Claim 1 does not require them. Avoiding infringement typically requires changing one of the independent claim essentials (notably monoammonium glycyrrhizinate, calcium acetate concentration band, or the sweetener/polyol selections).
References
[1] United States Patent 8,591,938 (claims as provided).
