US Patent 7,635,773 landscape: what the SAE-CD excipient composition and phosphate-free activated carbon process protect (and where design-arounds likely work)
United States Patent 7,635,773 is centered on (i) tight impurity specifications for sulfoalkyl ether cyclodextrins (SAE-CDs), expressed through phosphate content and UV/vis absorbance limits that act as proxies for drug-degrading and color-forming impurities, and (ii) a phosphate-free activated carbon treatment workflow used during manufacture to drive those impurity proxies down. The core claim scope is narrow by construction because it requires quantified thresholds (ppm/% levels) plus method-linked “degradation/color” absorbance limits at specified wavelengths and sample concentrations, but it is also broad in the sense that it covers a family of SAE-CD chemistries defined by a substitution pattern formula and multiple carbon-handling process variants.
What is US Patent 7,635,773 claiming about SAE-CD composition and UV absorbance impurities?
Claim 1: the foundational composition gate
Claim 1 requires a composition comprising an excipient plus an SAE-CD composition with three linked limitations:
- Phosphate impurity control: SAE-CD composition has <100 ppm phosphate.
- Drug-degrading agent control via UV/vis proxy: SAE-CD composition has absorption <0.2 A.U. attributable to a drug-degrading agent measured by UV/vis at 245–270 nm with:
- 300 mg SAE-CD per mL aqueous solution
- 1 cm path length cell
- “Excipient + SAE-CD” packaging: the claim ties the SAE-CD specification to a final composition context (“composition comprising an excipient and a SAE-CD composition”).
This is a classic “composition-by-property” approach: the patent protects not only chemical identity (SAE-CD) but also process-consistent impurity quality, with UV/vis windows converting analytical outcomes into enforceable claim boundaries.
Claim 2: color-forming agent proxy
Claim 2 depends on claim 1 and tightens the UV proxy for a different impurity class:
- Absorption <0.2 A.U. attributable to a color-forming agent
- measured by UV/vis at 320–350 nm
- 500 mg/mL aqueous solution
- 1 cm path length
Claim 3: impurity package beyond phosphate and UV
Claim 3 depends on claim 1 and further narrows the SAE-CD composition by adding multiple low-level impurities:
- <20 ppm sulfoalkylating agent
- <0.5 wt% underivatized cyclodextrin
- <1 wt% alkali metal halide salt
- <0.25 wt% hydrolyzed sulfoalkylating agent
This claim is important because it prevents arguments that a party can match only phosphate and UV while ignoring synthesis and hydrolysis residues.
Claims 4 and 7–9: additional measurement windows and tighter embodiments
- Claim 4 is a dependent duplicate of claim 1’s “drug-degrading agent” concept but includes a slightly different wavelength recitation (245–270 m-n), indicating the drafter’s attempt to preserve measurement flexibility while still staying in the same UV band.
- Claim 7 depends from claim 1 with a combined “hard spec” set:
- phosphate <50 ppm
- sulfoalkylating agent <10 ppm
- underivatized cyclodextrin <0.2 wt%
- alkali metal halide <0.5 wt%
- hydrolyzed sulfoalkylating agent <0.1 wt%
- plus color UV absorption <0.2 A.U. at 320–350 nm (500 mg/mL).
- Claims 8–9 create a more stringent subgroup:
- phosphate <10 ppm (claim 8)
- sulfoalkylating agent <2 ppm
- underivatized cyclodextrin <0.1 wt%
- alkali metal halide <0.2 wt%
- hydrolyzed sulfoalkylating agent <0.08 wt%
- and color UV <0.1 A.U. at 320–350 nm (also 500 mg/mL)
- Claim 9 tightens further:
- phosphate <5 ppm
- alkali metal halide <0.1 wt%
- hydrolyzed sulfoalkylating agent <0.05 wt%
Claims 5–6 and 10: the structural definition of the SAE-CD family
Claim 5 depends on claim 1 and defines the SAE-CD as Formula (I) with:
- p = 4, 5 or 6
- R1 groups independently = —OH or —O-(C2–C6 alkylene)-SO3−-T
- T = pharmaceutically acceptable cations
- at least one R1 = —OH, and at least one R1 = sulfonate-bearing ether substituent.
Claim 6 narrows the substituent and cation:
- R1 = —OH or —O-(C4 alkylene)-SO3−-T
- T = Na+ at each occurrence.
Claim 10 is a further embodiment specifying:
- sulfobutyl ether cyclodextrin
- average degree of substitution (DS) = 7
- phosphate <100 ppm
- drug-degrading UV absorption <0.2 A.U. at 245–270 nm (300 mg/mL)
Net effect: the patent protects SAE-CDs that match both (i) the substitution pattern and (ii) the impurity/UV quality parameters. That combination is the enforcement lever.
What does US 7,635,773 claim about manufacturing processes using phosphate-free activated carbon?
Claim 11: the process core
Claim 11 claims a manufacturing method for an excipient + SAE-CD composition with these stages:
(a) Sulfoalkylation reaction setup
- Mix cyclodextrin with a sulfoalkylating agent
- in presence of an alkalizing agent
- to form an aqueous reaction milieu containing:
- unwanted components
- drug-degrading impurities
(b) Separation / purification step
- remove unwanted components using one or more separations selected from:
- ultrafiltration, diafiltration, centrifugation, extraction, solvent precipitation, dialysis
- result: a partially purified aqueous solution containing SAE-CD plus drug-degrading impurities.
(c) Phosphate-free activated carbon treatment loop
- Treat partially purified solution with phosphate-free activated carbon two or more times
- to provide an SAE-CD composition with:
- phosphate <100 ppm
- drug-degrading UV absorption <0.5 A.U. at 245–270 nm (300 mg/mL)
- then
(d) Combine with excipient.
This claim is the main “manufacturing IP” pathway: it doesn’t just require that the final product has the specs, it claims the intermediate purification workflow and particularly the carbon step being phosphate-free and done two or more times.
Claim 12: color UV control in process
Depends on claim 11 and sets:
- color-forming agent UV absorption <0.5 A.U.
- at 320–500 nm (note the broad window recited)
- 500 mg/mL, 1 cm path.
Claim 13: combined phosphate + both UV constraints
A tighter process spec bundle:
- phosphate <50 ppm
- sulfoalkylating agent <10 ppm
- underivatized cyclodextrin <0.2 wt%
- alkali metal halide <0.5 wt%
- hydrolyzed sulfoalkylating agent <0.1 wt%
- drug-degrading UV absorption <0.5 A.U. at 245–270 nm
- plus color UV absorption <0.2 A.U. at 320–350 nm.
Claims 14–15: formula-limited process embodiments
These mirror claim 5–6, specifying:
- Formula (I) substitution pattern (claim 14)
- and the specific R1 (C4 alkylene ether) plus Na+ (claim 15).
Claims 16–18: activated carbon handling specifics create enforceable sub-scope
Claim 16 limits the carbon treatment mechanics to two alternatives:
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Batch add-and-separate loop
- add phosphate-free activated carbon while mixing
- separate carbon from solution
- repeat at least once until drug-degrading agent reaches target.
-
Flow-through recycling
- pass and recycle through a flow-through apparatus packed with phosphate-free activated carbon until target reached.
Claim 17 specifies that conducting includes passing and recycling two or more times, and each pass uses different mass of activated carbon.
Claim 18 quantifies carbon loading and time:
- activated carbon during conducting is about 12 wt% of SAE-CD
- conducted for at least about 2 hours.
Claim 19: product-by-process
Claim 19 is a product prepared by the process of claim 11, giving additional leverage: if a product is made using the claimed process, it inherits protection even when direct compositional testing is disputed.
How broad is the patent scope: property limits vs structural limits vs process limits?
Scope “stacking” makes invalidation-by-design harder, but design-arounds possible
The claim set stacks multiple constraints:
- Composition constraints: phosphate ppm plus UV absorbance thresholds tied to drug-degrading and color-forming impurities.
- Impurity package: sulfoalkylating agent, underivatized cyclodextrin, alkali metal halides, hydrolyzed sulfoalkylating agent.
- Structural constraints: Formula (I), p = 4–6, at least one —OH and at least one sulfonate-bearing ether substituent; plus embodiments with Na+ and C4 alkylene ether.
- Manufacturing constraints: phosphate-free activated carbon used two or more times, plus optional loop mechanics and quantitative carbon loading/time.
This makes “one parameter change” design-arounds less effective. But it also offers predictable release points:
- avoid phosphate-free activated carbon as the purification step,
- or avoid matching both UV absorbance thresholds in the same wavelength bands and at the same mg/mL sample prep,
- or adjust formulation to shift the claimed “composition comprising an excipient and SAE-CD composition” boundary (though composition inclusion alone is unlikely to avoid infringement if the SAE-CD itself meets the claim).
Where “composition-by-property” boundaries are tight
Because UV/vis absorbance limits are explicit, infringement analysis will turn on:
- the specific measurement protocol (wavelength range, sample concentration, path length),
- whether “absorption due to drug-degrading agent” and “due to color-forming agent” can be mapped to the same analytical decompositions used by the patentee.
From a freedom-to-operate standpoint, this is both a strength for enforcement and a risk for generics/alternatives that may have slightly different impurity profiles even if chemically similar.
Which parts of the claim set define the patent estate’s enforceable “hooks”?
Hook 1: phosphate impurity thresholds
Repeated across claims and embodiments:
- <100 ppm (claim 1 and 10)
- <50 ppm (claim 7 and 13)
- <10 ppm (claim 8)
- <5 ppm (claim 9)
This is likely tied to the activated carbon selection and/or phosphate removal strategy.
Hook 2: UV absorbance windows
Two channels:
- drug-degrading agent UV: 245–270 nm; thresholds <0.2 A.U. (claim 1/10) and <0.5 A.U. (process claim 11/13).
- color-forming agent UV: 320–350 nm; thresholds <0.2 A.U. (claim 2/7/13) and <0.1 A.U. (claim 8).
Process claim 12 expands color window to 320–500 nm with <0.5 A.U., increasing process capture.
Hook 3: activated carbon must be phosphate-free and used iteratively
Claim 11 makes “phosphate-free activated carbon” + “two or more times” central. Claims 16–18 further specify looping mechanics and quantitative carbon loading/time.
Hook 4: SAE-CD chemistry defined by Formula (I) and embodiments
Coverage includes:
- p = 4–6
- R1 mix of —OH and sulfonate-ether substituents
- embodiments for Na+ and C4 alkylene ether substitution and DS=7 sulfobutyl ether cyclodextrin.
How to assess infringement risk: what would likely satisfy each claim element?
Direct infringement: product sold as excipient-containing composition
If a supplier sells a SAE-CD excipient system (or offers it as part of a drug formulation) that meets:
- phosphate <100 ppm,
- UV/vis thresholds for drug-degrading and color-forming proxies,
then the product likely meets claims 1 and 2 at least.
The dependent claims 3, 7–9 add impurity package restrictions that narrow capture.
Process infringement: making SAE-CD via phosphate-free activated carbon loops
Manufacturers using phosphate-free activated carbon multiple times with UV-target-driven endpoints could trigger claim 11, with subclaims 16–18 capturing particular loop mechanics and carbon load/time conditions.
Product-by-process
If manufacturing records show use of the claim 11 process, claim 19 can extend risk even if the final product testing is contested, since “prepared by” is the test.
What patent landscape questions matter commercially for SAE-CD suppliers and drug formulators?
1) Is there likely a “blocking patent family” around SAE-CD impurity specs?
Patent 7,635,773’s claim architecture suggests it sits in a quality-control and manufacturing optimization family. The decisive differentiators are:
- phosphate-free activated carbon treatment,
- UV proxies for degradation and color,
- and tight impurity residue ceilings.
If a company’s SAE-CD manufacturing uses different adsorption media, different phosphate-removal strategies, or different termination criteria, they may be outside the key claim hooks even if their SAE-CD is otherwise similar.
2) Are design-arounds feasible by switching carbon chemistry or adding phosphate to carbon?
The claim requires “phosphate-free activated carbon.” Using carbon that contains phosphate above some threshold could, in theory, avoid literal satisfaction of that element, but it can increase phosphate impurity in the SAE-CD and fail the phosphate ppm limits anyway. So “switch the carbon” may not be sufficient unless the whole purification chain preserves low phosphate and low UV proxies.
3) Does the patent cover only sulfobutyl ether cyclodextrin or broader SAE-CDs?
It covers the SAE-CD family under Formula (I) and includes a specific sulfobutyl ether example (DS=7). That implies coverage is not confined to one SAE-CD species.
4) What about alternative purification steps
Claim 11’s separation step is broadly defined (many separation methods), but the activated carbon step is specific. If a process achieves low phosphate and low UV proxies without phosphate-free activated carbon, it may avoid the process claims while still requiring compositional clearance to avoid product claims.
5) Regulatory and QbD implications
For formulators using SAE-CD excipients, the patent’s reliance on analytical proxies means internal QC and supplier specifications become litigation-relevant. A supplier’s ability to document UV absorbance at defined sample concentrations will be central to any challenge.
Key Takeaways
- Core protection is “SAE-CD quality,” not just SAE-CD chemistry. Claims 1–3 and 7–9 lock phosphate and low UV absorbance proxies for drug-degrading and color-forming impurities.
- Manufacturing is protected via phosphate-free activated carbon used two or more times. Claim 11 is the primary process pathway, with tighter looping mechanics in claims 16–18.
- Scope is narrowed by quantified thresholds and defined analytical protocols. Wavelength windows, mg/mL sample prep, and 1 cm path length make infringement analysis highly measurement-dependent.
- Design-around strategies must address both phosphate and UV proxies, and likely cannot rely on changing only one step. Avoiding “phosphate-free activated carbon” alone may be insufficient if phosphate and UV specs are still met.
FAQs
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Does US 7,635,773 require both drug-degrading and color-forming UV limits to be met for the strictest embodiments?
Yes, for the dependent claims that combine them (e.g., claim 7/8/13), both channels are part of the recited limitations.
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Which UV wavelength windows define infringement risk for drug-degrading vs color-forming impurities?
Drug-degrading agent proxy: 245–270 nm. Color-forming agent proxy: 320–350 nm (and in one process claim, 320–500 nm).
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Are alkali metal halide residues part of the claimed impurity package?
Yes. Claims 3, 7–9 include ceilings on alkali metal halide salts (e.g., <1 wt% in claim 3; tighter limits in claims 7–9).
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Does the patent cover the manufacturing step only, or also the material sold downstream?
Both. Claim 11 protects the process, and claim 19 protects product-by-process; claims 1–10 protect the composition itself.
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Is the SAE-CD chemistry limited to one substitution pattern?
No. It is defined by Formula (I) with p = 4–6 and mixed R1 substitution types, with additional embodiments narrowing to specific substitution (C4 alkylene ether, Na+) and DS=7 sulfobutyl ether cyclodextrin.
References (APA)
- United States Patent 7,635,773.
