United States Patent 5,814,600: Claim Scope, Expiration, and Amylin-Insulin Patent Landscape

U.S. Patent No. 5,814,600 covers methods and compositions that combine insulin with amylin, including pramlintide, within specified molar-ratio and dose ranges. The broadest independent claims reach: (i) administering insulin and amylin to insulin-deficient mammals; and (ii) compositions containing both agents at a 1:1 to 67:1 insulin-to-amylin molar ratio. The patent does not claim insulin alone, amylin alone, or every combination therapy involving the two agents.

The patent is expired and does not create a current U.S. blocking right. Its historical importance was directed to replacement of the physiological co-secretion of insulin and amylin in diabetes treatment. The principal commercial product associated with this therapeutic concept was pramlintide acetate, marketed as Symlin and SymlinPen.

What does U.S. Patent 5,814,600 cover?

The patent covers two categories of subject matter:

Methods of treating mammals that have a need for insulin or a reduced ability to produce insulin.
Compositions containing insulin and amylin in defined proportions.

The claims are functionally and quantitatively limited. A product or treatment must satisfy both the biological definitions and the numerical limitations recited in the claims.

Claim group	Subject matter	Principal limitation
Claims 1-24	Treatment methods	Insulin plus amylin administered to an insulin-deficient or insulin-dependent mammal
Claims 3-8	Treatment-ratio subranges	Insulin:amylin ratios from 7:1 to 67:1 and narrower ranges down to 4:1 to 10:1
Claims 9-11, 17-19, 21, 24	Pramlintide and human-use limitations	Amylin includes 25,28,29 Pro-human amylin; certain claims require a human or diabetic human
Claims 12-21	Dose limitations	Amylin dose from at least 0.2 micrograms/kg/day, with narrower ranges and a 90 microgram/day human limitation
Claims 22-24	Plasma-level method claims	Amylin plasma levels equal approximately 3%-6% or 4%-7% of insulin plasma levels
Claims 25-32	Composition claims	Insulin and amylin provided in a 1:1 to 67:1 molar ratio, with narrower dependent ranges

The independent method claim is claim 1. The independent composition claim is claim 25. Claims 22 and 23 are also independent method claims, but they use a plasma-level relationship rather than a specified administered molar ratio.

What are the broadest claims in U.S. Patent 5,814,600?

Claims 1 and 25 are the broadest claims by structure, although each contains material limitations.

Claim 1: broad treatment method

Claim 1 requires:

A mammal having a need for insulin or a reduced ability to produce insulin;
Administration of an insulin;
Administration of an amylin;
An insulin biological activity shown by stimulation of glucose incorporation into glycogen in rat soleus muscle;
An amylin biological activity shown by suppression of glucose incorporation into glycogen in rat soleus muscle; and
An insulin-to-amylin molar ratio of approximately 1:1 to 67:1.

The word “comprising” makes claim 1 open-ended. Additional active ingredients, excipients, dosing steps, or treatment steps generally would not avoid the claim if all required insulin and amylin elements were present.

The claim is not limited to humans, diabetes, subcutaneous administration, a particular insulin sequence, or a particular amylin sequence. Those limitations appear in dependent claims.

Claim 25: broad composition claim

Claim 25 covers a composition containing:

An insulin with the specified glucose-incorporation activity;
An amylin with the specified glucose-suppression activity; and
An insulin-to-amylin molar ratio of approximately 1:1 to 67:1.

Unlike claim 1, claim 25 does not require that the composition be administered or that the patient have diabetes. It is a product claim directed to the insulin-amylin combination.

The composition claim does not expressly require a fixed-dose combination product, a single vial, a single syringe, a particular formulation, or a particular delivery device. A product supplied as a combination composition could fall within the claim if it satisfies the required ratio and biological limitations.

How do the ratio limitations narrow the patent claims?

The patent contains a nested series of ratio ranges.

Claim	Insulin:amylin molar ratio
Claims 1 and 25	About 1:1 to 67:1
Claims 3 and 26	About 7:1 to 67:1
Claims 4 and 27	About 1:1 to 40:1
Claims 5 and 28	About 2.5:1 to 35:1
Claims 6 and 29	About 5:1 to 25:1
Claims 7 and 30	About 5:1 to 10:1
Claims 8 and 31	About 4:1 to 10:1

The ratio is expressed as insulin relative to amylin. A formulation containing 100 molar units of insulin and 10 molar units of amylin has a 10:1 ratio and falls within claims 1, 4-8, and 25, 27-31, assuming the other claim elements are met.

The ranges overlap substantially. A composition at 8:1 falls within every ratio range from 7:1 to 67:1, 1:1 to 40:1, 2.5:1 to 35:1, 5:1 to 25:1, 5:1 to 10:1, and 4:1 to 10:1.

The ratio limitations create potential design-around paths for a live patent, including:

A ratio below 1:1 or above 67:1;
A product in which insulin and amylin are not provided as a composition;
Separate administration that does not meet the claimed ratio;
A product lacking the recited amylin activity; or
A treatment that cannot satisfy the relevant dose or plasma-level limitation.

Those approaches would require technical and legal analysis because the claims use “about,” which introduces tolerance around the numerical endpoints.

What is the significance of the rat soleus muscle assay?

The claims define insulin and amylin partly by biological activity rather than only by chemical identity.

The insulin must stimulate glucose incorporation into glycogen in rat soleus muscle. The amylin must suppress glucose incorporation into glycogen in the same assay system. These limitations distinguish the claimed agents by pharmacological function.

The assay language has several consequences:

It broadens the insulin limitation beyond human insulin or a named insulin analog.
It potentially reaches insulin analogs and modified insulins that retain the stated activity.
It broadens the amylin limitation beyond unmodified human amylin.
It may reach amylin analogs, including pramlintide, if the analog exhibits the claimed activity.
It creates an infringement and validity issue concerning how the assay is performed and what level of activity is sufficient.

The claims do not state a quantitative threshold for stimulation or suppression. That omission can create claim-construction disputes over whether any measurable activity is sufficient or whether the specification supplies a practical assay threshold.

What claims specifically cover pramlintide?

Claims 9-11, 17-19, 21, and 24 identify “25,28,29 Pro-human amylin.” This is the amylin analog generally known as pramlintide, in which proline substitutions occur at positions 25, 28, and 29 of human amylin.

The relevant dependent claims impose additional restrictions:

Some require only that the amylin comprise 25,28,29 Pro-human amylin.
Some require treatment of a human.
Some require treatment of a human suffering from diabetes mellitus or diabetes.
Some incorporate ratio limitations from the parent claims.
Claims 17-19 incorporate amylin dose limitations from claims 12-16.
Claim 21 requires at least approximately 90 micrograms of amylin per day in a human with diabetes.

The term “comprises” in these claims is important. A composition that contains pramlintide together with other amylin species may still satisfy the claim if pramlintide is present and the inherited limitations are met.

What dose ranges are protected?

Claims 12-21 add amylin dosing limitations.

Claim	Amylin dose
Claim 12	At least about 0.2 micrograms/kg/day
Claim 13	At least about 0.4 micrograms/kg/day
Claim 14	At least about 0.5 micrograms/kg/day
Claim 15	About 0.2 to 5 micrograms/kg/day
Claim 16	About 0.4 to 2 micrograms/kg/day
Claim 20	At least about 90 micrograms/day in a human with diabetes

These claims depend on claim 1 or a related dose claim. They therefore retain the insulin activity, amylin activity, treatment-purpose, and molar-ratio requirements unless the claim structure states otherwise.

The dose claims are not pure pramlintide dose claims. They require combined insulin-amylin treatment. A pramlintide product used without insulin would not satisfy these claims merely because its dose falls within one of the stated ranges.

What do claims 22 and 23 cover?

Claims 22 and 23 use plasma exposure rather than a fixed administered ratio.

Claim 22 requires an amount of amylin that results in amylin plasma levels of approximately 3% to 6% of insulin plasma levels. Claim 23 requires approximately 4% to 7%.

These claims raise different technical issues from claims 1 and 25:

The administered insulin-to-amylin ratio is not the sole determinant of infringement.
Pharmacokinetic variables become relevant, including absorption, clearance, half-life, injection timing, and renal function.
A formulation could meet the claim even if the administered molar ratio is outside one of the ratio ranges in claims 1-8, provided the resulting plasma relationship is satisfied.
Plasma sampling time and assay methodology may be material to infringement analysis.

Claims 22 and 23 are potentially difficult to enforce because plasma levels change over time. The claim language does not specify a single sampling time in the text supplied. The specification and prosecution history would be important to determine whether the limitation refers to peak concentration, steady-state concentration, average exposure, or another pharmacokinetic measure.

When did U.S. Patent 5,814,600 lose exclusivity?

U.S. Patent 5,814,600 issued on September 29, 1998. The patent is expired and cannot presently be asserted to block U.S. treatment or commercialization activity.

For a patent issued in 1998, the applicable U.S. term depends on the effective filing-date history and whether the application was subject to the pre-Uruguay Round Agreements Act transition rules, terminal disclaimers, or patent-term adjustment. Public patent records identify the patent as expired by the mid-2010s. The practical commercial consequence is the same: the claims no longer provide enforceable U.S. exclusivity.

Event	Date or status
Patent issued	September 29, 1998
Subject matter	Insulin-amylin combination methods and compositions
Current U.S. status	Expired
Current blocking effect	None from this patent
Historical relevance	Combination therapy, pramlintide dosing, and insulin-amylin ratios

Expiration of this patent does not eliminate later patents directed to pramlintide manufacture, formulations, devices, salt forms, dosing schedules, or separate delivery systems.

What is the Orange Book status of U.S. Patent 5,814,600?

The patent should not be treated as a current Orange Book barrier because it has expired. Historical Orange Book listing status must be distinguished from present enforceability.

Symlin, containing pramlintide acetate, received FDA approval under NDA 021332 in 2005 for use as an adjunct to mealtime insulin in adults with type 1 and type 2 diabetes. The FDA-approved product was supplied as an injectable solution, including pen presentations in later product versions.[1]

An Orange Book listing, if previously made for a patent covering an approved method of use, would not extend the patent beyond its statutory term. FDA listing and patent enforceability are separate questions:

The FDA determines whether a patent is listed for an approved drug product.
The USPTO and federal courts determine patent term and enforceability.
An expired patent cannot support a current injunction against generic or follow-on entry.
An unexpired method-of-use patent could still create a regulatory certification issue even if the product patent had expired.

Which companies challenged or could challenge this patent?

There is no current Paragraph IV exposure from U.S. Patent 5,814,600 because the patent has expired.

During the patent’s effective term, a generic or follow-on applicant could have challenged the patent under the Hatch-Waxman framework if the patent had been listed for the relevant FDA-approved product. Potential theories would have included:

Non-infringement based on a ratio outside the claimed range;
Failure to satisfy the rat soleus activity limitations;
Failure to meet the amylin dose or plasma-level limitations;
Anticipation by earlier insulin-amylin treatment disclosures;
Obviousness based on known physiological co-secretion of insulin and amylin;
Written-description or enablement challenges to broad functional definitions; and
Indefiniteness challenges concerning “about,” “suitable molar ratio,” and plasma-level measurements.

The claim set would have presented a narrower challenge target than a composition patent covering pramlintide itself because a challenger could avoid infringement through a product configuration or dosing regimen that did not meet the combination limitations.

What patent landscape surrounds insulin-amylin combination therapy?

The surrounding landscape includes multiple patent categories rather than one unified right.

Amylin and pramlintide composition patents

Earlier Amylin-related patents addressed:

Human amylin;
Amylin analogs;
Proline-substituted amylin analogs;
Methods for reducing aggregation;
Pharmaceutical salts and injectable formulations; and
Treatment of diabetes using amylin or amylin analogs.

These patents were more directly relevant to the molecular identity and pharmaceutical development of pramlintide than U.S. Patent 5,814,600, which focuses on combined insulin-amylin administration.

Insulin product patents

Separate patent estates covered:

Human insulin;
Insulin lispro;
Insulin aspart;
Insulin glargine;
Insulin detemir;
Insulin degludec;
Concentrated insulin formulations;
Stabilizers and excipients; and
Injection devices and cartridges.

A combination product could face independent patent risk from the insulin component even after U.S. Patent 5,814,600 expired.

Formulation patents

Formulation claims may cover:

Co-formulated insulin and pramlintide;
pH-controlled injectable solutions;
Stabilized peptide mixtures;
Preservative systems;
Adsorption-control excipients;
Separate-chamber devices; and
Pen or cartridge delivery systems.

Insulin and amylin have different formulation and stability characteristics. A commercially practical fixed-dose product may therefore require formulation technology that is separate from the expired combination-ratio claims.

Method-of-use patents

Later patents may address:

Pramlintide use in type 1 diabetes;
Pramlintide use in type 2 diabetes;
Timing relative to meals;
Insulin dose reduction when initiating pramlintide;
Weight-management effects;
Hypoglycemia-reduction protocols; and
Patient selection and titration.

A generic applicant could avoid a method-of-use patent through a section viii carve-out if the relevant use is not necessary for the proposed labeling. That regulatory strategy would depend on the exact approved indication and listed patent claims.

How strong was the patent estate?

U.S. Patent 5,814,600 had moderate historical scope but limited present value because it expired.

Factor	Assessment
Claim breadth	Broad at the independent-claim level, but constrained by biological activity and ratio limitations
Product coverage	Meaningful for insulin-amylin compositions within the stated ratios
Pramlintide coverage	Stronger in dependent claims expressly reciting 25,28,29 Pro-human amylin
Formulation coverage	Limited; no detailed excipient, container, device, or stability limitations in the supplied claims
Method coverage	Broad treatment-purpose language, narrowed by combined administration and ratio requirements
Design-around potential	Material, particularly through ratio, dosing, delivery, or composition changes
Current enforceability	None because the patent is expired
Biosimilar relevance	Low; pramlintide is a synthetic peptide drug, not a biologic biosimilar reference product
Generic relevance	Historical relevance to ANDA and Paragraph IV analysis; no current blocking effect

The strongest claim positions were likely claims directed to a human diabetic patient receiving pramlintide with insulin at a defined ratio or dose. The weakest positions were the broad functional claims if prior art disclosed combined insulin-amylin therapy and if the specification did not adequately support the full scope of the assay-defined agents.

What generic launch risks exist today?

The expired patent does not prevent generic or follow-on pramlintide entry. Current risk would instead arise from:

Unexpired patents listed for the relevant pramlintide product;
Manufacturing patents covering peptide synthesis or purification;
Formulation patents;
Device patents covering pens, cartridges, or delivery systems;
Regulatory exclusivity;
FDA requirements for demonstrating pharmaceutical equivalence and bioequivalence; and
Commercial manufacturing complexity.

Pramlintide is a peptide drug. A follow-on applicant may face more demanding analytical and clinical comparability work than an ordinary small-molecule generic, even if the product is submitted through an abbreviated pathway. That development burden is a market-entry barrier, but it is not an enforceable patent right created by U.S. Patent 5,814,600.

What manufacturing and geographic IP barriers remain?

U.S. Patent 5,814,600 is limited to U.S. rights and has no current blocking effect in the United States. Foreign counterpart patents must be assessed separately because foreign filing dates, patent terms, annuity payments, prosecution outcomes, and supplementary protection regimes differ.

Potential remaining barriers include:

Country-specific pramlintide composition patents;
Process patents for peptide synthesis;
Crystallization, purification, or impurity-control patents;
Formulation patents;
Device patents;
Trademark and regulatory rights associated with Symlin; and
Trade secrets involving manufacturing yield, scale-up, and quality control.

A freedom-to-operate review should separate expired combination claims from live process and formulation rights. The absence of enforceability for the U.S. composition and method claims does not establish freedom to operate for a particular manufacturing process or delivery device.

What litigation and settlement issues affect the patent?

U.S. Patent 5,814,600 is no longer capable of supporting a current infringement injunction. Any historical litigation or settlement involving the patent would have commercial significance only for the period before expiration, unless the agreement imposed independent contractual restrictions.

A settlement involving an expired patent cannot revive patent exclusivity. It could still contain separate obligations, but those would be contract questions rather than patent-term rights.

No current Paragraph IV litigation can delay entry based solely on this patent. A future dispute would need to involve a different, unexpired patent or a non-patent regulatory or contractual right.

How does this patent compare with a pramlintide product patent?

Issue	U.S. Patent 5,814,600	Pramlintide product patent
Primary subject	Combined insulin-amylin treatment and composition	Chemical identity or formulation of pramlintide
Required insulin	Yes	Not necessarily
Required amylin	Yes	Yes, often specifically defined
Ratio limitation	Yes	Usually not the central limitation
Patient limitation	Present in dependent claims	May be absent or method-specific
Dose limitation	Present in dependent claims	May cover a formulation or dosing regimen
Current status	Expired	Must be checked patent by patent
Main design-around	Change ratio, delivery, dose, or composition structure	Use a nonclaimed process, formulation, or analog

Key Takeaways

U.S. Patent 5,814,600 claims insulin-amylin combination treatment and compositions.
Claims 1 and 25 are the principal broad claims.
The central quantitative limitation is an insulin-to-amylin molar ratio of approximately 1:1 to 67:1.
Narrower claims cover ratios including 5:1 to 10:1 and 4:1 to 10:1.
Dependent claims specifically address 25,28,29 Pro-human amylin, the pramlintide analog.
Additional claims cover amylin doses from approximately 0.2 micrograms/kg/day and a human diabetic dose of at least approximately 90 micrograms/day.
Claims 22 and 23 use amylin plasma levels equal to approximately 3%-7% of insulin plasma levels.
The patent issued September 29, 1998 and is expired.
It creates no current U.S. patent barrier to generic, follow-on, or combination-product entry.
Current risk must be assessed against later pramlintide, formulation, manufacturing, device, and method-of-use patents.
Pramlintide is a synthetic peptide drug, so biosimilar analysis is less direct than for a monoclonal antibody or other licensed biologic.

FAQs About U.S. Patent 5,814,600

Does U.S. Patent 5,814,600 cover Symlin?

It covers methods and compositions that combine insulin with amylin within specified biological, ratio, and dose limitations. Because Symlin contains pramlintide, the dependent claims reciting 25,28,29 Pro-human amylin are particularly relevant historically.

Does the patent cover insulin by itself?

No. The claims require both insulin and amylin. Insulin-only treatment does not satisfy the combination requirement.

Does the patent cover pramlintide by itself?

No. The claims require administration or composition with insulin. A pramlintide-only product is outside the supplied claims.

Can a company launch a fixed-ratio insulin-pramlintide product without this patent?

Yes, this patent is expired. The company would still need to evaluate live patents covering pramlintide, insulin, formulation technology, manufacturing processes, devices, and approved methods of use.

Is a biosimilar application required for pramlintide?

Not necessarily. Pramlintide is a synthetic peptide drug rather than a conventional reference biologic such as a monoclonal antibody. The applicable FDA pathway depends on the product, reference listing, formulation, and statutory classification.

References

U.S. Food and Drug Administration. (2005). Symlin (pramlintide acetate) injection, NDA 021332: Prescribing information.
U.S. Patent and Trademark Office. (1998). U.S. Patent No. 5,814,600, methods and compositions for treating diabetes.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book.
U.S. Code, Title 35, §§ 154, 271, and 282.
U.S. Code, Title 21, § 355.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	155689	⤷ Start Trial
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Austria	197764	⤷ Start Trial
Australia	1328692	⤷ Start Trial
Australia	1663092	⤷ Start Trial
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Details for Patent: 5,814,600

Summary for Patent: 5,814,600