US 5,840,680: Critical claim analysis and U.S. patent landscape (AspB28 insulin + protamine + phenol/m-cresol crystals; zinc optional)

What does US 5,840,680 actually claim?

US 5,840,680 claims crystalline forms of AspB28 human insulin made with protamine and a phenolic component (phenol, m-cresol, or both). The claims then broaden protection to formulations (aqueous suspensions) and therapeutic methods for diabetes via administering those compositions.

Core claim set (verbatim-structure summary)

Claim	Scope anchor	Essential components (must be present)	State/form factor
1	Crystal composition	AspB28 human insulin + protamine + phenol and/or m-cresol	Crystalline
2	Crystal composition (dependent)	Claim 1 + zinc	Crystalline
3	Formulation (dependent of claim 1)	Crystals of claim 1	Pharmaceutical formulation
4	Formulation (dependent of claim 2)	Crystals of claim 2	Pharmaceutical formulation
5	Formulation (state limitation)	Claim 3 + aqueous suspension	Suspended in aqueous medium
6	Formulation (state limitation)	Claim 4 + aqueous suspension	Suspended in aqueous medium
7	Formulation (excipient set)	Claim 3 + isotonic agent and/or buffer	Adds formulation excipients
8	Formulation (excipient set)	Claim 4 + isotonic agent and/or buffer	Adds formulation excipients
9	Excipient specificity	Claim 7 + isotonic agent (NaCl and/or glycerol) + buffer (disodium monohydrogen phosphate)	Specific formulation recipe
10	Excipient specificity	Claim 8 + same NaCl/glycerol + buffer (disodium monohydrogen phosphate)	Specific formulation recipe
11	Formulation (dual insulin)	Claim 3 + dissolved AspB28 human insulin	Crystals plus dissolved insulin
12	Formulation (dual insulin)	Claim 4 + dissolved AspB28 human insulin	Crystals plus dissolved insulin
13	Medical use	Administer formulation of claim 3	Treat diabetes mellitus
14	Medical use	Administer formulation of claim 4	Treat diabetes mellitus

How strong are the claim elements as patent boundaries?

The enforceability hinges on whether the “crystals” are defined narrowly enough to require a specific physical/structural state and whether the “AspB28” substitution is limiting enough against insulin analogs and mixtures.

1) “AspB28 human insulin” is a specific molecular species

AspB28 is the physiologic insulin sequence variant at position B28 (Asp at B28 is characteristic of human insulin; many older references emphasize insulin structural variants at B28 to distinguish from “insulin-like” or modified forms used in prior art). This term can function as a meaningful limit that blocks coverage of analogs that do not contain Asp at B28, and it can block certain insulin salts/forms if they are argued not to be “AspB28 human insulin” as claimed.

Patent boundary risk: If the specification treats AspB28 human insulin as indistinguishable from ordinary human insulin or broadly includes human insulin forms already known, the difference-versus-prior-art may shrink.

2) “Protamine + phenol and/or m-cresol” tracks long-standing insulin formulation chemistry

Protamine association with insulin to extend duration is a known insulin strategy. Phenol and m-cresol are classic antimicrobial stabilizers in insulin products. The claim ties these ingredients together specifically in a crystalline form, but the ingredient set itself is not exotic.

Patent boundary risk: Many competitors and earlier products already used protamine and phenolic stabilizers in insulin suspensions. The legal novelty is more likely placed on the crystal form and on the specific AspB28/protamine/phenol-m-cresol crystallization outcome.

3) “Crystals comprising …” makes physical form the likely novelty carrier

Claim 1’s novelty must come from crystallization conditions and the resulting crystal morphology/structure. Without objective crystal characterization limits in the claims (particle size, X-ray diffraction patterns, lattice parameters, polymorph identity, etc.), “crystals” can be vulnerable to arguments that prior art also yields crystals, or that the claim term is too functional.

Patent boundary risk: If the claims do not recite objective crystal-identifying parameters, “crystals” can be attacked as indefinite, or broad enough that it captures routine crystallization outcomes known in earlier insulin-protamine systems.

4) Zinc is optional (dependent claim 2)

Claim 2 adds zinc to claim 1 crystals. This creates a second tier of coverage. If earlier art uses zinc in insulin formulations, claim 2 may face prior-art overlap. Still, dependence keeps claim 2 narrower.

5) Formulation claims (3-12) are broad on presentation

Claims 3-4 cover “pharmaceutical formulation comprising crystals” with no further state limitation until claims 5-6. Claims 5-6 require an aqueous suspension, but insulin products commonly use aqueous suspensions, which can be a prior-art magnet.

Claims 7-10 specify typical isotonic/buffer choices, using a short list:

isotonic agent: sodium chloride and/or glycerol
buffer: disodium monohydrogen phosphate

This is recipe-like but still constrained to conventional excipients. If earlier art uses these exact excipients with the same crystal system, the dependent formulation claims may not add much patentability.

Claims 11-12 add “further comprising dissolved AspB28 human insulin,” which is a meaningful limitation if prior art only presents insulin in solid crystal form.

6) Method claims (13-14) are tied to administration of the claimed formulation

These are standard medical-use claims that typically inherit limitations from the product claim. If the product claims are weak/invalid, the method claims usually fall with them.

What are the most likely prior-art pressure points?

Because the claims combine well-known insulin formulation elements, the landscape question becomes: did earlier patents or publications already describe AspB28 human insulin crystallized with protamine and stabilized with phenol and/or m-cresol, including zinc, and did they claim or disclose formulations as aqueous suspensions and therapeutic use?

Pressure point A: “Insulin + protamine” in crystals

If any earlier U.S. patents taught protamine-insulin crystalline complexes (even without using the exact AspB28 phrasing), claim 1’s novelty may collapse. The defense would be that earlier crystals were different (e.g., different insulin species, different stabilization chemistry, or different crystal structure).

Pressure point B: Phenol/m-cresol in protamine-insulin

Phenol and m-cresol are antimicrobial staples. If prior art crystallized insulin-protamine complexes in the presence of phenol and/or m-cresol, claim 1 may read on those disclosures if the “crystals” were recognized or implicit.

Pressure point C: Zinc-containing insulin-protamine systems

Zinc is widely used in insulin compositions (including insulin-zinc complexes). If prior art includes zinc in insulin-protamine complexes, claim 2 could overlap significantly.

Pressure point D: Dependent claims are conventional formulation recipes

Claims 7-10 use typical isotonic and buffer agents for insulin injections. If the only “distinctiveness” is excipient selection, these dependent claims can be attacked for lacking inventive step beyond the underlying crystal form.

Pressure point E: “Dissolved insulin” co-present

Claims 11-12 require dissolved AspB28 human insulin alongside the crystals. Some earlier suspensions may have only crystalline insulin-protamine complexes without free dissolved insulin. That requirement can be a differentiator if earlier products did not include free dissolved insulin at the same time.

How does the claim structure affect freedom-to-operate (FTO)?

The claims are layered:

Product: crystalline AspB28 insulin + protamine + phenol/m-cresol (± zinc)
Formulation: that crystalline product in aqueous medium with routine excipients (and possibly dissolved insulin)
Method: administering those formulations to treat diabetes

If a competitor avoids one ingredient

If they use insulin analogs not considered “AspB28 human insulin,” they can design around molecular scope.
If they omit phenol and m-cresol (using different preservatives), they can design around the claim 1 phenolic member.
If they avoid protamine, they can design around directly.

If a competitor uses the same ingredients but different physical form

If their product is a colloidal suspension or non-crystalline complex, they may avoid “crystals” (though this becomes a technical infringement question).

If a competitor includes zinc

They may infringe claim 2 more readily. If they exclude zinc entirely, they may still infringe claim 1.

If a competitor uses the same recipe but different buffer/isotonic agents

Claims 9-10 are constrained; using other isotonic agents or different buffers may avoid those dependent claims, while still potentially infringing the broader claims 7-8 (which only require “isotonic agent” and/or “buffer,” not necessarily NaCl/glycerol + disodium monohydrogen phosphate).

What does the landscape likely look like around this patent?

US 5,840,680 sits in the center of two dense patent clusters:

insulin-protamine duration and crystal/complex formation
insulin formulation with phenolic preservatives, aqueous suspension, buffers, isotonic agents
zinc-containing insulin systems
medical-use claims for diabetes treatment via insulin formulations

In practice, competitors face a broad risk zone because:

The ingredient lists are conventional.
The differentiator must be the crystalline identity and how AspB28 insulin participates in crystal formation with protamine and phenolic stabilizers.

Where are the highest-value claim invalidity arguments likely to concentrate?

These typically target:

Anticipation (35 U.S.C. §102): a single earlier reference discloses the same crystal composition and/or the same formulation and/or the same method.
Obviousness (35 U.S.C. §103): combining known insulin-protamine crystallization approaches with routine phenol/m-cresol inclusion and conventional excipients.

Most direct invalidity route

Prior art already discloses “crystals” or “crystalline complexes” made from human insulin + protamine, stabilized with phenol and/or m-cresol, optionally including zinc, and formulated as an aqueous suspension for diabetes treatment.

If prior art is close but not identical

The likely weak spot for the patent owner is whether the crystal term can be treated as not genuinely limiting due to:

lack of objective structural descriptors in the claims (if the claims do not recite crystal metrics),
or broad interpretations that capture routine crystallization outcomes.

Competitive assessment: how to interpret the claim scope for R&D decisions

Design-around levers that map cleanly to the claim text

Swap the preservative system away from phenol and m-cresol (to avoid claim 1 directly).
Avoid zinc where the formulation would otherwise be a claim 2/4 match.
Avoid protamine or change the association mechanism.
Change insulin away from “AspB28 human insulin” (if analogs are acceptable clinically).

What will likely be hardest to design around

If a product uses insulin + protamine + phenol/m-cresol and forms a crystalline solid phase, the remaining defenses become technical and evidentiary:
- whether the product truly forms “crystals,”
- whether the crystals are those comprising AspB28 human insulin,
- and whether the formulation has the required dissolved insulin component (claims 11-12).

Key Takeaways

US 5,840,680’s protection centers on crystalline compositions of AspB28 human insulin with protamine and phenol and/or m-cresol, with zinc in dependent claims.
The broad formulation claims largely follow routine insulin injection formulation practice (aqueous suspension, isotonic agents, phosphate buffer).
The patent’s main differentiator versus known insulin formulation chemistry is the crystalline identity and the specific ingredient pairing in that crystalline form.
For FTO, the cleanest design-arounds track the claim words: avoid phenol/m-cresol, avoid protamine, avoid zinc, or use a different insulin molecular species.
The method claims likely live or die with the underlying product claims.

FAQs

Which claim is the key independent claim?
Claim 1 is the independent claim covering the core crystalline composition: AspB28 human insulin + protamine + phenol and/or m-cresol.
Does the patent cover zinc-containing crystals?
Yes. Claim 2 adds zinc to the claim 1 crystal composition, and claims 4-6 and 8-10 build from claim 2.
Are the formulation claims limited to specific excipients?
Claims 7-8 require isotonic agent and/or buffer without limiting identity. Claims 9-10 lock the excipient identities to sodium chloride and/or glycerol (isotonic) and disodium monohydrogen phosphate (buffer).
Do the claims require dissolved insulin in the formulation?
Only claims 11-12 require additional dissolved AspB28 human insulin. Claims 3-10 do not.
Are the method claims separate inventions?
Claims 13-14 are therapeutic uses that require administration of the claimed pharmaceutical compositions (claim 3 or claim 4 respectively), so they depend on the product limitations.

References (APA)

U.S. Patent 5,840,680. (n.d.). Crystals of AspB28 human insulin with protamine and phenol/m-cresol (and zinc) for pharmaceutical formulations and methods for treating diabetes.

Applicant	Tradename	Biologic Ingredient	Dosage Form	BLA	Approval Date	Patent No.	Expiredate
Novo Nordisk Inc.	NOVOLOG MIX 70/30	insulin aspart protamine and insulin aspart	Injectable Suspension	021172	November 01, 2001	⤷ Start Trial	2016-12-11
Novo Nordisk Inc.	NOVOLOG MIX 70/30	insulin aspart protamine and insulin aspart	Injectable Suspension	021172	May 03, 2002	⤷ Start Trial	2016-12-11
Novo Nordisk Inc.	NOVOLOG MIX 50/50	insulin aspart protamine and insulin aspart	Injectable Suspension	021810	August 26, 2008	⤷ Start Trial	2016-12-11
>Applicant	>Tradename	>Biologic Ingredient	>Dosage Form	>BLA	>Approval Date	>Patent No.	>Expiredate

Country	Patent Number	Estimated Expiration
Austria	E176482	⤷ Start Trial
Australia	6995794	⤷ Start Trial
Germany	10199011	⤷ Start Trial
Germany	122006000015	⤷ Start Trial
Germany	122006000017	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration

Patent: 5,840,680

Summary for Patent: 5,840,680