Details for Patent: 6,051,259

US Patent 6,051,259: What Is Claimed and How Broad Is the Scope?

US 6,051,259 claims a sustained-release human growth hormone (hGH) formulation built around two required structural elements:

1. a polymer matrix of poly(lactide-co-glycolide) (PLGA), and
2. particles of zinc-complexed hGH dispersed in that matrix, with the zinc-to-hGH molar ratio constrained to 4:1 to 100:1, and an hGH loading of 10 to 30 wt% in the composition.

The patent also claims methods of delivering hGH using that same formulation. The claim set is short and tightly tethered to the zinc complex and PLGA formulation parameters, which narrows design-around space relative to broader PLGA-hGH controlled-release concepts that do not require a defined metal-to-protein complex stoichiometry.

What Exactly Do Claims 1-6 Cover (Composition Scope)?

Claim 1: Core composition definition

Independent claim 1 defines the sustained-release composition as having:

• Polymer matrix component (a):

  • Poly(lactide-co-glycolide) (PLGA)

• Drug particle component (b):

  • Particles of zinc-complexed human growth hormone
  • Zinc cation component-to-hGH molar ratio between about 4:1 and about 100:1

• Dispersion condition:

  • zinc-complexed hGH particles are dispersed within the PLGA

• Drug loading requirement:

  • hGH proportion is between 10 and 30 weight percent of the sustained release composition

Claim 1 is a composite of three quantitative constraints (Zn:protein ratio; hGH wt%; PLGA presence). These constraints drive the practical infringement boundary.

Claim 2: Specific zinc stoichiometry

• Limits the Zn:hGH molar ratio to about 10:1.

Claim 3: Optional second metal cation, not complexed to hGH

• Adds a “second metal cation component” that:
  • is not complexed to hGH
  • is dispersed within the polymer matrix
  • is present at at least about 1% by weight of polymer

This claim introduces an additional formulation axis (co-dispersed metal salt/ion) without requiring complexation to hGH. It can broaden coverage for multi-ion formulations built on the same zinc-complexed hGH particles.

Claim 4: PLGA lactide:glycolide ratio

• Sets PLGA composition to lactide:glycolide = 1:1.

Claim 5: “Unblocked” PLGA

• Requires PLGA to be unblocked.

Claim 6: PLGA molecular weight window

• Requires PLGA molecular weight about 6,000 to about 31,000 Daltons.

Composition-dependent claim nesting

The dependent claims stack as follows:

• Claim 1 (core) → Claim 2 (Zn ratio 10:1)
• Claim 1 + Claim 3 (adds optional second metal cation)
• Claim 1 + Claim 4 (PLGA 1:1) → Claim 5 (unblocked) → Claim 6 (MW range)

Net effect: the independent claim is already constrained; the dependents further constrain polymer chemistry and/or additives.

How Broad Is the Stoichiometry Constraint (4:1 to 100:1)?

The zinc cation component-to-hGH molar ratio range in claim 1 is broad in absolute terms but still a hard numerical boundary. In practical formulation work, zinc complexation depends on:

• zinc salt identity and counterion,
• complexation conditions (pH, ionic strength),
• protein particle formation process,
• residual uncomplexed zinc,
• analytically defined “complexed” fraction.

Claim 1 does not explicitly define how “zinc-complexed” is measured. It does, however, anchor infringement to the ratio.

Practical scope implications

• A formulation with zinc:hGH outside 4:1 to 100:1 is positioned outside claim 1 (at least on this parameter).
• A formulation with the same zinc ratio but hGH wt% outside 10–30 wt% is outside claim 1.
• A formulation with the same drug loading and zinc ratio but different polymer (not PLGA) is outside claim 1.
• A formulation that uses zinc-complexed hGH but changes particle dispersion approach (not “dispersed within” PLGA) risks non-infringement, but that language is typically satisfied by typical encapsulation/dispersion formats.

What Exactly Do Claims 7-12 Cover (Method Scope)?

Claim 7: Delivery method

Claim 7 is a method claim framed as:

• Administer to a subject in need thereof
• a composition for sustained release comprising the same elements as claim 1:
  • PLGA
  • zinc-complexed hGH particles
  • zinc:hGH molar ratio 4:1 to 100:1
  • dispersed within PLGA
  • hGH content 10–30 wt%

Claims 8-12 are coextensive dependent method claims

• Claim 8: Zn:hGH molar ratio about 10:1
• Claim 9: Adds second metal cation (not complexed to hGH) in polymer ≥1 wt% of polymer
• Claim 10: PLGA lactide:glycolide 1:1
• Claim 11: PLGA is unblocked
• Claim 12: PLGA MW 6,000–31,000 Da

Net effect: method coverage tracks the formulation coverage with no additional delivery mechanism limitation (no injection device constraints, injection route, dosing interval, etc.). That increases the risk profile for any clinician administration of an infringing formulation.

Core Claim Elements: A Claim-Chart Style Breakdown

Where This Sits in the Landscape: How Strong Is Its “Patent Gravity”?

US 6,051,259 is a composition-and-method patent with key differentiators:

• Metal complexation is part of the formulation claim (not just a processing method).
• The zinc:hGH molar ratio range is explicit.
• The hGH loading window is explicit.
• The sustained-release carrier is not generic “biodegradable polymer”; it is PLGA with optional further definition (1:1 lactide:glycolide; unblocked; specific MW band).

This combination reduces interpretive elasticity. Courts and examiners often struggle when claims are broad but unclear; here, the numeric constraints tighten claim construction.

Likely infringement pathways

• A product that uses PLGA microspheres or similar devices containing zinc-complexed hGH with target zinc stoichiometry and protein loading will map directly to claim 1.
• A product that includes additional metal ions in the matrix but keeps hGH not complexed with the second metal can still fall under claim 3/9 if zinc-complexed hGH particles and the core stoichiometry/loading exist.

Likely design-around pathways (high-level)

Based on the claim geometry, the most direct levers are:

• Change zinc:hGH molar ratio outside 4:1–100:1
• Change hGH wt% outside 10–30 wt%
• Replace PLGA with another polymer system
• Use a zinc-associated approach that is not “complexed” (if chemically and analytically justified) or that does not form particles of zinc-complexed hGH as claimed

(These are scope levers derived from the claim language, not recommendations.)

Potential Claim Construction Frictions (What Typically Becomes Litigated)

1) “Zinc-complexed” and “molar ratio”

Claims use “zinc cation component-to-human growth hormone molar ratio” and require particles of “zinc-complexed hGH.” In disputes, the key issues tend to be:

• What counts as “zinc cation component” (total zinc? labile zinc? zinc released under test conditions?).
• What fraction of hGH is actually complexed versus simply exposed to zinc salt.
• How the ratio is calculated (input formulation vs measured composition vs post-processing residual content).

2) “Particles dispersed within the polymer matrix”

If the formulation is truly molecularly dispersed (no particulate phase), that may avoid “particles” language. If it is microspheres/aggregates/solid domains containing zinc-complexed hGH, “particles dispersed” is likely met.

3) hGH wt%

“Proportion of hGH in the sustained release composition” is quantitative. Process-induced variability (e.g., residual solvent, different excipient fractions) can affect the wt% definition.

4) “Unblocked” PLGA

“Unblocked” is a polymer end-group concept that can hinge on chemistry and specification (e.g., free ends vs protected ends). That matters mainly for dependents 5/11.

What the Patent Actually Protects: A Concentrated Target

US 6,051,259 is not a broad PLGA-hGH sustained release patent. It is a zinc-stoichiometry PLGA-hGH sustained-release patent.

• The independent claim requires both the zinc-complexed hGH particulate element and two numerical windows (Zn:hGH and hGH wt%).
• The dependents add specific PLGA grade descriptors (1:1, unblocked, MW band) and/or a second metal that is not complexed to hGH and is present at ≥1% by weight of polymer.

That claim structure indicates the patent was drafted to capture a specific formulation concept, not the entire universe of controlled-release hGH systems.

Key Takeaways

• Independent claims 1 and 7 cover a sustained-release composition and delivery method built on PLGA and particles of zinc-complexed hGH dispersed in PLGA.
• Coverage hinges on two explicit numeric constraints: Zn:hGH molar ratio 4:1–100:1 and hGH 10–30 wt%.
• Dependent claims tighten the scope by specifying Zn:hGH about 10:1, adding a second metal cation at ≥1 wt% of polymer (not complexed to hGH), and constraining PLGA to 1:1 lactide:glycolide, unblocked, and 6,000–31,000 Da.
• The patent’s protection is highly targeted; the most straightforward design-around routes follow the claim’s numeric and structural boundaries (zinc stoichiometry, protein loading, polymer identity, and particulate complex presence).

FAQs

1) Is US 6,051,259 limited to PLGA only?

Yes. Claim 1 requires a polymer matrix comprising poly(lactide-co-glycolide).

2) Does the zinc range apply to every claim?

The zinc cation-to-hGH molar ratio 4:1 to 100:1 is required in claims 1 and 7. Dependent claim 2/8 narrows it to about 10:1.

3) What is the hGH loading window in the core claims?

Claims 1 and 7 require hGH in the sustained release composition at 10 to 30 weight percent.

4) Can a formulation include other metal cations and still fall within the patent?

Yes. Claims 3 and 9 add a second metal cation that is not complexed to hGH and is dispersed in the polymer at ≥1% by weight of polymer.

5) Does the patent specify PLGA grade details?

The dependents do. Claims 4/10 require lactide:glycolide = 1:1, claims 5/11 require unblocked PLGA, and claims 6/12 require MW about 6,000 to about 31,000 Da.

References

[1] United States Patent No. 6,051,259.