Details for Patent: 4,761,237

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Summary for Patent: 4,761,237

Title:	Peritoneal dialysis solution containing carbohydrate polymers
Abstract:	A peritoneal dialysis solution which comprises a water solution of physiological pH, and having physiological salts and metabolizable carbohydrate polymers in concentrations sufficient to safely effect the removal of solutes and water from a patient by peritoneal dialysis.
Inventor(s):	Steven R. Alexander, W. Michael Myers
Assignee:	Baxter International Inc
Application Number:	US07/065,656
Patent Claim Types: see list of patent claims	Use; Formulation;

United States Patent 4,761,237: Scope, Claim Logic, and US Patent Landscape for Peritoneal Dialysis Using Starch-Derived Glucose Polymers

What does US 4,761,237 claim, in plain claim architecture?

US 4,761,237 claims methods of peritoneal dialysis (PD) that address a known PD engineering constraint: sustaining ultrafiltration (UF) over time as osmotic pressure declines.

The claims are built around one core technical lever and three layered constraint tiers:

1. Core UF mechanism: maintain an osmotic gradient that drives water removal by diffusion across the peritoneal membrane.
2. Osmotic agent identity: use nonionic starch hydrolyzate glucose polymers.
3. Molecular weight constraint: polymers must have average degree of polymerization (DP) ≥ 4 to slow polymer loss and thus sustain osmotic pressure.
4. Optional combinatorial UF booster: claim 2 adds glucose in combination with the polymer.
5. Quantified formulation window: claims 3 and 4 lock the osmolarity range (272 to 700 mOsm/L; and a narrower 279 to 480 mOsm/L).

The patent’s novelty posture is not “peritoneal dialysis with an osmotic agent” in general, but peritoneal dialysis with a starch-derived nonionic glucose polymer fraction selected by DP to reduce osmotic pressure decay rate and sustain UF.

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What are the claim elements and how do they limit infringement?

Claim 1 (base claim): DP-selective nonionic starch hydrolyzate polymers for sustained UF

Claim 1 requires all of the following steps and limitations:

(a) Dialysate base salts to enable solute diffusion

• Introducing into the peritoneal cavity a solution containing physiological salts at concentrations sufficient to remove solutes by diffusion from blood across the peritoneal membrane into the dialysate.

(b) Osmotic support using polymer osmotic pressure and reduced osmotic decay

• Reducing the rate of osmotic pressure decrease over time to maintain a desired UF rate.
• Achieved by introducing into the solution nonionic starch hydrolyzate glucose polymers that:
  • Are present in concentrations sufficient to create an osmotic pressure to effect water removal by diffusion.
  • Have average DP of at least 4.
  • DP ≥ 4 is tied to slow removal by diffusion into blood versus polymers with DP < 4.

Claim 1 defines infringement as a method performance (not a product per se): a party practices the method when they perform PD with such a dialysate and achieve the stated functional result (UF maintenance via reduced osmotic pressure decay attributable to DP ≥ 4 polymer persistence).

Key constraining facts for scope

• Polymer must be:
  • Nonionic
  • Starch hydrolyzate glucose polymer
  • Average DP ≥ 4
• Performance hinges on:
  • Maintaining osmotic pressure sufficiently over time for desired UF
  • The mechanism includes relative diffusion loss vs DP < 4.

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Claim 2 (dependent): add glucose with polymers

Claim 2 adds:

• In step (b), introducing glucose in combination with the nonionic starch hydrolyzate polymers.

This narrows scope to formulations or treatment regimens where both:

• glucose is present, and
• the starch hydrolyzate polymers (DP ≥ 4 per Claim 1) are present.

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Claim 3 (dependent): osmolarity range for polymers/glucose

Claim 3 limits:

• Polymer-containing step (b) must create osmolarity about 272 to about 700 mOsm/L.

This is a quantitative cap/floor on the dialysate osmotic strength.

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Claim 4 (dependent): narrower osmolarity sub-range

Claim 4 narrows claim 3 to:

• about 279 to about 480 mOsm/L.

This is the tightest formulation window and likely the most commercially relevant working range.

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What is the technical “center of gravity” for claim breadth?

The claims are broadest where they are least numerically constrained:

• Broadest: Claim 1 (no numeric osmolarity, no glucose requirement).
• Medium: Claim 2 (glucose required).
• Narrowest: Claims 3-4 (osmolarity windows), with Claim 4 as the most constrained.

The most decisive breadth determinant is the polymer selection using DP ≥ 4. If an accused regimen uses:

• a different type of osmotic agent (e.g., ionic polymers, amino acid solutions, different carbohydrate polymers),
• or a starch hydrolyzate fraction with average DP < 4, then it can fall outside the literal limitation.

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How does the DP ≥ 4 limitation function as a scope boundary?

The claim uses a mechanistic rationale to distinguish DP fractions:

• Nonionic starch hydrolyzate glucose polymers with DP ≥ 4 are said to sustain osmotic pressure over time because of relatively slow removal by diffusion across the peritoneal membrane.
• The comparison is explicitly against polymers with DP < 4.

Practically, this creates two infringement risk buckets:

1. Material composition risk (DP determination)

   • The “average DP” must be at least 4.
   • Litigation risk will turn on how the polymer fraction’s DP is measured and what “average DP” means for the product fraction in use.

2. Functional/clinical performance risk (osmotic pressure decay and UF maintenance)

   • The method recites functional performance: maintaining desired UF rate by reducing osmotic pressure decrease rate.
   • Evidence of UF persistence linked to the polymer’s slower diffusion loss strengthens enforceability.

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What product/formulation equivalents are likely within or outside the claim?

Within likely scope (based on wording)

• Dialysate solutions for PD that include:
  • physiological salt base for diffusion of solutes,
  • nonionic starch hydrolyzate glucose polymers with average DP ≥ 4,
  • optionally glucose,
  • with osmolarity within the claimed window (if claims 3 or 4 are asserted).

Likely outside literal scope

• Use of osmotic agents that are:
  • not nonionic,
  • not starch hydrolyzate glucose polymers,
  • or a polymer distribution whose average DP is < 4.
• Formulations that use osmotic agents but do not rely on starch hydrolyzate glucose polymers to “reduce the rate of decrease of osmotic pressure … due to relatively slow removal.”

Because claims are drafted as “starch hydrolyzate glucose polymers” and “average DP ≥ 4,” similar intent alone is insufficient for literal coverage.

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What does Claim 1 implicitly require about the treatment setting?

The claimed method is explicitly:

• performed by peritoneal dialysis
• involving introduction of a solution into the peritoneal cavity of a patient.

So the claim targets clinical PD procedures rather than in vitro systems, and it requires a treatment delivery into the peritoneal space.

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US 4,761,237 vs. the broader PD osmotic agent landscape

The claim is positioned within a crowded area: osmotic agents in PD have included glucose, icodextrin, amino acid solutions, and other polymeric or carbohydrate-based osmotics. The differentiator here is the use of nonionic starch hydrolyzate glucose polymers with DP ≥ 4 and the functional result of slowing osmotic pressure decay via polymer retention.

Where it likely sits conceptually

• It is a carbohydrate polymer osmotic approach.
• It focuses on polymer chain length (DP) as the retention lever.
• It seeks to overcome the decline in osmotic driving force over time that occurs when the osmotic agent rapidly dissipates.

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What is the practical freedom-to-operate map for US claims as stated?

A regulatory or R&D team evaluating PD dialysate options can treat US 4,761,237 as creating three actionable design constraints:

1. Nonionic starch hydrolyzate glucose polymer identity

   • If the osmotic agent is not in that category, the regimen avoids the central limitation.

2. Average DP must be at least 4 (if you are trying to avoid infringement, you must not meet it)

   • Reformulating to a fraction with average DP < 4 can reduce risk, but it must be controlled and demonstrated relative to the claimed “average DP” measurement.

3. Osmolarity window risks

   • If the regimen’s osmolarity falls in 272–700 mOsm/L (or 279–480 mOsm/L), it increases claim 3/4 exposure, assuming other limitations are also met.

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What is known and what is not determinable from the claim text alone

From the claim text provided, the scope can be parsed precisely at the claim-element level (DP, nonionic starch hydrolyzate glucose polymers, osmolarity ranges, optional glucose, method of PD).

What cannot be derived from the claim excerpt alone is:

• whether the patent has additional dependent claims beyond claim 4,
• whether there are composition claims (the excerpt only shows method claims 1-4),
• the priority date, prosecution history, examiner rejections, and claim construction anchors,
• whether the patent was cited/overruled in later reexaminations,
• whether competitors’ products are explicitly constrained by this patent in practice.

Per your input constraints, the analysis below focuses strictly on the claim scope you provided.

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Key Takeaways

• US 4,761,237 claims PD methods that maintain ultrafiltration by reducing osmotic pressure decay over time.
• The osmotic agent must be nonionic starch hydrolyzate glucose polymers with average DP ≥ 4, which the claim links to slower polymer removal by diffusion.
• Claim 2 adds glucose with the polymers.
• Claims 3 and 4 impose osmolarity windows: 272–700 mOsm/L and 279–480 mOsm/L.
• From a freedom-to-operate standpoint, the hardest boundary is polymer identity and DP ≥ 4; the next boundary is osmolarity if claims 3 or 4 are asserted.

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FAQs

1) Does US 4,761,237 cover any peritoneal dialysis osmotic solution?

No. It covers PD methods where the osmotic support is provided by nonionic starch hydrolyzate glucose polymers with average DP ≥ 4, used to slow osmotic pressure decrease and sustain UF.

2) Is glucose required for infringement?

No. Glucose is only required for Claim 2. Claim 1 does not require glucose.

3) What is the most decisive technical limitation?

The polymer’s average degree of polymerization (DP) of at least 4 and its characterization as nonionic starch hydrolyzate glucose polymers.

4) Do the osmolarity ranges apply to all claims?

No. The osmolarity ranges are in Claims 3 and 4. Claim 1 does not recite a numeric osmolarity window.

5) Is the claim directed to a composition or a procedure?

It is directed to a method of performing peritoneal dialysis (procedure), not a stand-alone composition claim in the excerpt provided.

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References (APA)

1. United States Patent 4,761,237. Claims 1-4 (per your provided claim text).

Drugs Protected by US Patent 4,761,237

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate

International Family Members for US Patent 4,761,237

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Canada	1172563
Germany	3276048
European Patent Office	0083360