United States Patent 4,486,420: Claim Scope, Patent Expiration, and Low-Molecular-Weight Heparin Landscape

U.S. Patent No. 4,486,420 covers selected low-molecular-weight heparin fractions with enhanced anti-factor Xa activity relative to whole anticoagulant activity, defined by molecular weight, solvent fractionation behavior, structural NMR signals, biological activity ratios, and antithrombin III binding. It also covers pharmaceutical compositions, injectable use, and manufacturing processes.

The patent was granted in 1984 and, as a pre-Uruguay Round Agreement Act patent, had a 17-year term from grant, subject to any recorded adjustments or disclaimers. Its ordinary term therefore expired in approximately 2001. The patent does not create a current U.S. blocking right against generic or follow-on low-molecular-weight heparin products. Its principal value today is historical and evidentiary: it helps establish the technical origin of selective anti-Xa heparin fractions and may remain relevant to freedom-to-operate analyses involving historical development, inventorship, priority, or patent-family strategy.

What technology does U.S. Patent 4,486,420 protect?

The patent protects low-molecular-weight heparinic mucopolysaccharide fractions, now generally discussed within the low-molecular-weight heparin, or LMWH, field.

The claimed fractions are characterized by a combination of:

Molecular weight of approximately 2,000 to 10,000 daltons.
Solubility in 55° to 61° GL aqueous alcohol.
Insolubility in alcohol.
Anti-Xa-to-USP anticoagulant activity ratio of at least 3.
Reduced whole anticoagulant activity relative to conventional heparin.
Specific glucosamine, iduronic acid, glucuronic acid, sulfate, and N-acetyl structural features.
Defined carbon-13 and proton NMR signals.
In certain claims, selective binding to antithrombin III.
Physiologically acceptable salts, particularly sodium and calcium salts.

The invention is directed to separating or enriching heparin fractions that inhibit factor Xa more selectively than they prolong global coagulation measurements. That distinction is central to the patent. Conventional unfractionated heparin has both anti-Xa and anti-thrombin activity. The patent seeks fractions with a higher anti-Xa effect per unit of overall anticoagulant activity.

The patent document is the controlling source for the claim language, examples, drawings, and disclosed analytical methods (U.S. Patent No. 4,486,420, 1984).

How are the claims organized?

The 29 claims fall into five principal categories.

Claim group	Claims	Subject matter
Composition claims	1-20	Heparinic mucopolysaccharide fractions and salts
Pharmaceutical composition claims	21-24	Compositions containing the fractions in a carrier
Treatment claims	25-26	Controlling thrombosis by administration, including injection or infusion
Manufacturing claims	27-29	Alcohol fractionation, gel filtration, and antithrombin III affinity selection
Narrow analytical or potency claims	2-19	NMR patterns, molecular-weight ranges, potency thresholds, and activity ratios

Claim 1 is the principal composition claim. Claims 2 through 20 narrow claim 1 through additional NMR, potency, molecular-weight, salt, and biological-activity limitations.

Claim 21 is a composition claim that incorporates the subject matter of the earlier composition claims. Claims 22 through 24 narrow the pharmaceutical composition by anti-Xa potency or solution concentration.

Claim 25 covers a therapeutic method for controlling thrombosis through selective inhibition of factor Xa. Claim 26 limits administration to injection or infusion.

Claim 27 is the broadest process claim. Claims 28 and 29 add gel filtration and antithrombin III affinity purification.

What does claim 1 require?

Claim 1 is cumulative. A product would need to satisfy the structural, physicochemical, and biological limitations together.

The claim requires a heparinic mucopolysaccharide fraction that:

Has a molecular weight of about 2,000 to 10,000 daltons.
Dissolves in 55° to 61° GL water-alcohol.
Is insoluble in alcohol.
Has an anti-Xa-to-USP activity ratio of at least 3.
Has specified sulfated glucosamine and iduronic acid relationships.
Shows the recited carbon-13 NMR resonance signals.
Has a lower whole anticoagulant activity than heparin.
Has improved in vivo antithrombotic activity measured through anti-Xa activity per milligram.
Includes physiologically acceptable salts.

The claim is therefore broader than a claim limited to one commercial product, but narrower than a generic claim to all LMWHs. The product must fall within the defined molecular-weight and activity ranges and must also exhibit the required structural fingerprint.

A major claim-construction issue is whether the NMR language is treated as a true structural limitation or as evidence of the claimed carbohydrate architecture. The prosecution history, specification, and original examples would be important in any historical infringement analysis. Based on the claim text alone, the NMR limitations materially narrow the scope.

What do claims 2 through 20 add?

NMR-defined fractions

Claims 2, 4, 5, 6, and 7 rely on NMR spectra shown in the patent figures. These claims may be difficult to apply without reproducing the patent’s testing conditions, including solvent, frequency, reference standard, concentration, temperature, and assignment methodology.

Claim 2 adopts the spectrum shown in Figure 1a. Claim 7 refers to any of the spectra in Figures 11, 12, 14, or 15. These claims create possible factual disputes over:

Whether the spectrum must match exactly or only materially.
Whether peak intensity is required.
Whether the testing method must replicate the disclosed 20 MHz carbon-13 conditions.
Whether later analytical instruments produce equivalent results.
Whether a complex mixture can satisfy a spectrum limitation despite batch variability.

Claim 3 addresses primary carbon positions in the 6-position and resonance behavior near the 100 ppm region. Claims 4 through 6 add signals in the 75 ppm and 60 ppm regions and proton resonances at approximately 4.8, 5.2, and 5.4 ppm.

Potency and activity-ratio limitations

Claims 9 through 19 define multiple potency profiles.

Claim	Principal limitation
9	USP titer about 45 units/mg; anti-Xa about 160 units/mg; ratio about 3.55
10	USP titer below about 10 units/mg; anti-Xa about 161 units/mg
11	Anti-Xa/USP ratio at least 6; anti-Xa at least 300 units/mg
12	Ratio at least 10
13	Ratio at least 50
14	Ratio at least 130
15	Claim 11 profile with anti-Xa not less than about 50 units/mg
16	Ratio above 18; anti-Xa at least 900 units/mg
17	Ratio above 65; anti-Xa at least 1,300 units/mg
18	USP no more than about 13 units/mg; anti-Xa 135-160 units/mg; ratio 13-16; molecular weight 4,000-8,000 daltons
19	USP no more than about 6 units/mg; anti-Xa at least 44 units/mg; ratio above about 9; molecular weight 4,000-8,000 daltons

These claims create substantial enablement and definiteness questions if read literally across the full numerical ranges. Biological titers can vary with assay conditions, reference standards, calibration lots, and manufacturing batches. Terms such as “about,” “not less than,” and “does not exceed” provide some flexibility but do not eliminate the need for validated testing.

Claim 15 is internally awkward because it depends on claim 11, which already requires anti-Xa activity of at least 300 units/mg, while claim 15 recites an anti-Xa value of at least about 50 units/mg. The lower 50-unit threshold does not expand the scope of claim 11. It is effectively redundant unless the claim hierarchy or dependency was corrected during prosecution.

Salt claims

Claim 20 identifies sodium and calcium salts. This limitation is commercially relevant because LMWH products are commonly supplied as sodium or calcium salts, but the expired status of the patent means the limitation does not presently prevent use of those salt forms.

What pharmaceutical products and dosage forms are implicated?

Claims 21 through 24 cover therapeutic compositions containing the claimed fractions in a pharmaceutically acceptable carrier.

Claim 21 is broad as to the carrier and incorporates the subject matter of claims 1 through 20. Claim 22 requires anti-Xa potency above approximately 100 units/mg. Claims 23 and 24 cover solutions at approximately 1,000 to 100,000 Yin-Wessler units per milliliter, with a narrower range of approximately 5,000 to 50,000 units per milliliter in claim 24.

Claim 25 covers treatment of thrombosis by selectively inhibiting factor Xa. Claim 26 identifies injection or infusion. The claim set therefore reaches:

Injectable anticoagulant solutions.
Infusion products.
Sodium or calcium heparinic salts.
Products supplied in prefilled syringes or vials, to the extent they contain a claimed fraction.
Therapeutic use against thrombotic conditions.

The claims do not expressly require a particular disease, dose, dosing interval, syringe configuration, preservative, buffer, or packaging system.

What manufacturing processes are protected?

Claims 27 through 29 protect a multistage fractionation and purification process.

Alcohol fractionation

Claim 27 requires:

Starting heparin mucopolysaccharides with a molecular weight of approximately 2,000 to 50,000 daltons.
Mixing the material in a 55° to 61° GL aqueous-alcoholic medium.
Separating the liquid medium containing dissolved mucopolysaccharides.
Precipitating the soluble mucopolysaccharides by alcoholic precipitation.
Recovering fractions with an increased anti-Xa-to-USP ratio.

The process is not limited to a particular alcohol by the supplied claim language, although the specification may narrow the technical interpretation through examples.

Gel filtration

Claim 28 adds gel filtration of the aqueous solution and recovery of a fraction with a further increased anti-Xa-to-USP ratio.

This limitation may distinguish the patent from processes that use only chemical depolymerization, chromatographic separation, or membrane filtration.

Antithrombin III affinity purification

Claim 29 adds contact with antithrombin III immobilized on a support. Fractions with higher Yin-Wessler activity are selectively retained and later eluted.

This is a functional affinity-purification limitation. A process using a different affinity ligand, a different immobilization chemistry, or a different selection mechanism would require separate analysis. A process that produces a similar LMWH product through chemical depolymerization without the claimed alcohol fractionation and antithrombin III selection would not necessarily fall within claim 29.

How strong is the patent estate?

The patent’s historical scope was technically significant but legally narrow in several respects.

Strength factor	Assessment
Product coverage	Moderate; broad concept, narrowed by NMR and activity limitations
Process coverage	Moderate to strong against the specific disclosed fractionation sequence
NMR limitations	Potentially strong for identity testing, but vulnerable to reproducibility disputes
Biological potency limitations	Dependent on assay standards and test conditions
Pharmaceutical composition claims	Broad in formulation terms but dependent on the underlying fraction
Method-of-use claims	Limited to factor Xa-selective thrombosis treatment
Current enforceability	None after expiration of the patent term
Orange Book relevance	No current blocking effect established from the supplied record
Biosimilar relevance	Historical only; not a current biologic exclusivity barrier

The patent does not appear, from the claim set supplied, to claim a single fully defined molecular structure. It claims a heterogeneous polysaccharide fraction through a combination of measurable properties. That approach can capture products with overlapping analytical and biological characteristics, but it also creates proof burdens.

When did U.S. Patent 4,486,420 lose exclusivity?

The patent was granted in 1984. Under the patent-term rules applicable to patents filed before June 8, 1995, the term generally ran for 17 years from grant, subject to patent-term adjustment, terminal disclaimers, or other recorded changes (U.S. Patent and Trademark Office, n.d.-a).

On that basis, the ordinary expiration date was approximately 2001. The exact enforceable expiration date should be taken from the USPTO Patent Center file and the face of the issued patent, including any term disclaimer or adjustment. The patent is not an active exclusion right in the United States today.

Expiration eliminates ordinary infringement liability for activities occurring after expiration. It does not eliminate the patent’s relevance to:

Historical infringement disputes.
Ownership and inventorship questions.
Priority disputes.
Validity analysis of continuation or divisional patents.
Regulatory history.
Prior-art and obviousness analysis.
Technology licensing records.

What is the Orange Book status of the patent?

The Orange Book lists patents submitted for approved drug products under the Hatch-Waxman framework. A patent covering a historical LMWH fraction is not automatically an Orange Book-listed patent for every later heparin or LMWH product.

The supplied claim set does not identify a specific FDA-approved product, NDA, patent-use code, or Orange Book listing. The patent should therefore not be treated as an Orange Book barrier without a product-specific FDA listing and NDA record. FDA’s Orange Book is the relevant source for current listed patents and exclusivity associated with approved small-molecule drug applications (U.S. Food and Drug Administration, n.d.-a).

For LMWH products, regulatory characterization can also depend on whether the product is treated as a drug, a biological product, or a complex mixture requiring product-specific equivalence evidence. That classification does not revive an expired patent.

Are there Paragraph IV challenges or generic launch risks?

A Paragraph IV certification is relevant when an ANDA applicant challenges an unexpired patent listed for an approved reference drug. Because U.S. Patent 4,486,420 expired approximately two decades ago, it does not present a current Paragraph IV launch barrier.

The principal generic-entry risks for LMWH products are more likely to involve:

Product-specific FDA requirements.
Demonstration of sameness or equivalence for complex polysaccharide mixtures.
Assay comparability.
Molecular-weight distribution.
Anti-Xa and anti-IIa activity.
Impurities and process-related variants.
Source material and animal-origin controls.
Manufacturing consistency.
Other later patents covering formulations, devices, manufacturing processes, or dosing regimens.

An expired composition patent can still be relevant to whether a competitor’s product is scientifically similar, but it cannot independently support a current U.S. injunction.

Does the patent create biosimilar risk?

The patent is not a current biosimilar exclusivity barrier. The Purple Book concerns licensed biological products and biosimilar or interchangeable products, while LMWH products occupy a more complicated regulatory position than conventional monoclonal-antibody biologics (U.S. Food and Drug Administration, n.d.-b).

Any current competitive risk would arise from:

Product-specific FDA approval requirements.
Regulatory classification.
Manufacturing and analytical comparability.
Other unexpired patents.
State substitution rules.
Procurement contracts and supply reliability.

The 4,486,420 patent itself is expired and does not create a live biosimilar or follow-on biologic exclusion period.

Which competing LMWH products should be compared?

The relevant commercial comparators include enoxaparin, dalteparin, tinzaparin, nadroparin, and other LMWH products. They differ in source material, depolymerization method, molecular-weight distribution, anti-Xa-to-anti-IIa profile, regulatory status, and patent history.

Product	Active material	Typical commercial positioning	Relevance to Patent 4,486,420
Enoxaparin	Enoxaparin sodium	Low-molecular-weight heparin with strong anti-Xa activity	May overlap conceptually, but product-specific composition and process claims require separate analysis
Dalteparin	Dalteparin sodium	LMWH with distinct molecular-weight and activity profile	Requires product-specific structural comparison
Tinzaparin	Tinzaparin sodium	LMWH prepared through a distinct depolymerization approach	Process differences may reduce relevance of process claims
Nadroparin	Nadroparin calcium	Calcium LMWH with product-specific specifications	Calcium salt is expressly contemplated by claim 20, but the patent is expired
Parnaparin and other LMWHs	Product-specific salts	Regional or specialty anticoagulant products	Overlap cannot be determined from salt form alone

A product cannot be assessed against the patent solely by its anti-Xa activity or molecular weight. The NMR, solvent behavior, structural composition, and process limitations must also be evaluated.

What licensing and settlement issues are associated with the patent?

The supplied information does not identify a license, assignment chain, settlement agreement, consent judgment, or patent litigation involving U.S. Patent 4,486,420. The patent’s assignee, ownership transfers, and related agreements must be confirmed through the USPTO assignment database and court records.

Because the patent expired approximately in 2001, any historical license would now have limited forward-looking value unless it included:

Know-how rights.
Trade secrets.
Manufacturing technology.
Regulatory data rights.
Improvements.
Trademark rights.
Confidential technical documentation.
Royalty obligations surviving patent expiration.

Patent expiration does not necessarily terminate separate contractual restrictions, although enforceability depends on the agreement and applicable law.

What manufacturing and intellectual-property barriers remain after expiration?

The patent no longer blocks use of the disclosed fractionation concept. Practical barriers remain in manufacturing and regulatory execution.

Manufacturing barriers

LMWH production requires control over:

Starting heparin source and animal tissue supply.
Molecular-weight distribution.
Degree and location of sulfation.
Depolymerization or fractionation conditions.
Residual solvents and reagents.
Batch-to-batch anti-Xa and anti-IIa activity.
Endotoxin and impurity levels.
Sterility and particulate control.
Salt form and injectable stability.

These barriers can support trade-secret protection even when the foundational patent has expired.

Later patent barriers

A freedom-to-operate review should search later patents covering:

Specific depolymerization chemistry.
Enoxaparin manufacturing processes.
Chromatographic purification.
Injectable formulations.
Prefilled syringes and delivery devices.
Dosing regimens.
Combination anticoagulant therapy.
New indications.
Analytical release specifications.
Process controls and impurity removal.

The existence of an expired foundational patent does not establish freedom to operate for later patents.

What is the geographic coverage?

U.S. Patent 4,486,420 provides U.S. territorial rights only. Related foreign applications may have existed in Europe, Canada, Japan, or other jurisdictions, but their scope and expiration dates must be analyzed separately.

Patent-family searches should distinguish:

Priority applications.
National-stage or convention filings.
Continuations.
Divisionals.
Continuation-in-part applications.
Foreign counterparts.
Later improvement patents.

Expiration of the U.S. patent does not establish expiration of every foreign counterpart, although patents from the same early priority period are generally also likely to be expired.

Key Takeaways

U.S. Patent 4,486,420 claims selective anti-Xa low-molecular-weight heparin fractions, related pharmaceutical compositions, thrombosis treatment, and fractionation processes.
Claim 1 requires a cumulative combination of molecular weight, solvent behavior, activity ratio, carbohydrate structure, and NMR characteristics.
Claims 27 through 29 cover alcohol fractionation, gel filtration, and antithrombin III affinity purification.
The patent was granted in 1984 and ordinarily expired around 2001 under the pre-1995 patent-term rules.
It is not a current U.S. blocking patent for LMWH development, generic entry, biosimilar competition, or injectable anticoagulant commercialization.
Orange Book and Paragraph IV consequences cannot be inferred from this patent alone because the supplied record does not identify an FDA-listed product or current listed patent.
Current risk is more likely to arise from later process, formulation, device, dosing, regulatory, or manufacturing patents.
Historical technical overlap with enoxaparin, dalteparin, tinzaparin, nadroparin, or other LMWHs cannot be determined from anti-Xa potency or molecular weight alone.

FAQs

Does U.S. Patent 4,486,420 cover enoxaparin?

Not automatically. Enoxaparin would require comparison against the patent’s full product limitations, including NMR characteristics, solvent behavior, structural composition, molecular-weight range, and anti-Xa-to-USP ratio. The patent’s expiration also eliminates current infringement exposure based on this patent.

Can a company commercialize a calcium LMWH despite claim 20?

Yes, claim 20 expressly identifies calcium salts, but the patent expired approximately in 2001. Current commercialization would require review of later patents and FDA requirements.

Does the patent claim unfractionated heparin?

No. The claims are directed to selected heparinic mucopolysaccharide fractions, generally within a low-molecular-weight range, with enhanced anti-Xa selectivity and defined structural or analytical properties.

Are the NMR limitations likely to matter in a historical infringement case?

Yes. The NMR limitations could determine whether a product falls within claims 2 through 7 and may also inform construction of claim 1. Testing conditions, peak assignments, mixture variability, and the interpretation of “as shown” would be central issues.

Can the disclosed fractionation process still be used?

The expired patent does not prevent use of the disclosed process. A current freedom-to-operate analysis must still identify later patents covering specific alcohol systems, gel-filtration materials, affinity supports, process controls, or product specifications.

References

U.S. Patent No. 4,486,420. (1984). Heparinic mucopolysaccharides, process for preparing same and pharmaceutical compositions thereof. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.-a). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
U.S. Food and Drug Administration. (n.d.-b). Purple Book: Database of licensed biological products. https://purplebooksearch.fda.gov/
United States Patent and Trademark Office. (n.d.-a). Patent term adjustment and patent term calculation. https://www.uspto.gov/patents/laws/patent-term-calculator
United States Patent and Trademark Office. (n.d.-b). Patent Center. https://patentcenter.uspto.gov/

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
France	78 31357	Nov 06, 1978
France	79 18873	Jul 20, 1979

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	227417	⤷ Start Trial
Austria	17586	⤷ Start Trial
Austria	26450	⤷ Start Trial
Australia	540433	⤷ Start Trial
Australia	543679	⤷ Start Trial
Australia	6392080	⤷ Start Trial
Australia	6787081	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,486,420

Summary for Patent: 4,486,420