US Patent 5,965,581: Tirofiban Injection Claims, Scope, Expiration, and Patent Landscape

US Patent 5,965,581 protects narrow intravenous tirofiban formulations rather than the tirofiban molecule broadly. Its claims focus on two low-dose compositions containing tirofiban, sodium chloride, sodium citrate dihydrate, and citric acid, with specified osmolality and pH ranges. The patent also covers intravenous antiplatelet treatment using two of those formulations.

The patent is associated with tirofiban hydrochloride, marketed in the United States as Aggrastat. Its patent term has expired, eliminating current US patent-based barriers to generic tirofiban injection products. The principal commercial risks now arise from regulatory substitution, formulation execution, manufacturing controls, and market competition rather than from US Patent 5,965,581.

What drug and formulation does US Patent 5,965,581 protect?

The claimed active ingredient is tirofiban, chemically identified in the claims as:

2-S-(n-butylsulfonylamino)-3-[4-[4-(piperidin-4-yl)butyloxy]phenyl]propionic acid

The claims also cover the hydrochloride monohydrate salt. Tirofiban is a small-molecule glycoprotein IIb/IIIa platelet aggregation inhibitor administered intravenously in acute coronary syndrome and during percutaneous coronary intervention.

The commercial product is tirofiban hydrochloride injection. The FDA-approved product label identifies Aggrastat as tirofiban hydrochloride injection in a ready-to-use intravenous formulation. The claimed excipient system is consistent with a parenteral solution designed to control tonicity, buffering, pH, and chemical stability. [1]

Core formulation elements

Element	Claim 1 / 3 / 7 formulation	Claim 2 / 4 / 8 formulation
Tirofiban free acid	About 0.25 mg/mL	About 0.05 mg/mL
Tirofiban hydrochloride monohydrate equivalent	About 0.28 mg/mL	About 0.056 mg/mL
Sodium chloride	About 8 mg/mL	About 9 mg/mL
Sodium citrate dihydrate	About 2.7 mg/mL	About 0.54 mg/mL
Citric acid, anhydrous	About 0.16 mg/mL	About 0.032 mg/mL
Osmolality	About 250-310 mOsmol/kg	About 255-345 mOsmol/kg
pH	5.5-6.5	5.5-6.5
Administration	Intravenous	Intravenous

The free-acid and hydrochloride-monohydrate concentrations are corresponding forms of the same active pharmaceutical ingredient. The salt quantities are higher because the hydrochloride monohydrate includes hydrochloride and water-of-crystallization mass.

What are the independent claim categories in US 5,965,581?

The patent has three principal claim groups:

Composition claims.
Composition claims directed to the hydrochloride monohydrate form.
Method-of-treatment claims requiring intravenous administration.

Claims 1 and 2 recite formulations using the active ingredient by reference to the free-acid chemical name. Claims 3, 4, 7, and 8 recite compositions formed by combining the hydrochloride monohydrate with the specified excipients.

Claims 5 and 6 are method claims. They require intravenous treatment of a patient with a pharmaceutically effective amount of the composition of claim 1 or claim 2 to inhibit platelet aggregation.

Claim architecture

Claims	Claim type	Primary limitation
1	Composition	0.25 mg/mL tirofiban, excipients, pH and osmolality
2	Composition	0.05 mg/mL tirofiban, excipients, pH and osmolality
3	Composition	0.28 mg/mL tirofiban hydrochloride monohydrate formulation
4	Composition	0.056 mg/mL tirofiban hydrochloride monohydrate formulation
5	Method	IV platelet-aggregation inhibition using claim 1 composition
6	Method	IV platelet-aggregation inhibition using claim 2 composition
7	Composition	Claim 3-type formulation with pH adjustment language
8	Composition	Claim 4-type formulation with pH adjustment language

How narrow are the formulation claims?

The claims are narrow and formulation-specific. A potentially infringing product would generally need to satisfy the active-ingredient identity, approximate concentration, excipient composition, pH, and osmolality limitations.

The claims do not broadly cover every tirofiban formulation. A product using a different buffer, materially different sodium chloride concentration, different pH, or materially different tirofiban concentration may fall outside the literal claim scope. The word "about" creates a numerical tolerance issue, but it does not eliminate the requirement that the accused formulation remain reasonably close to the claimed concentration.

Active ingredient limitation

The claims are directed to tirofiban and its hydrochloride monohydrate salt. They do not cover unrelated glycoprotein IIb/IIIa inhibitors such as abciximab or eptifibatide.

A formulation containing tirofiban hydrochloride may still be relevant to claims that recite the free acid if the active species in solution is chemically equivalent. The outcome would depend on claim construction, product composition, and whether the formulation meets the other limitations. Claims 3, 4, 7, and 8 provide clearer coverage for the hydrochloride monohydrate form.

Concentration limitations

The patent covers two principal strength levels:

Approximately 0.25 mg/mL tirofiban free acid, corresponding to approximately 0.28 mg/mL hydrochloride monohydrate.
Approximately 0.05 mg/mL tirofiban free acid, corresponding to approximately 0.056 mg/mL hydrochloride monohydrate.

A formulation with a different strength could avoid literal infringement if it falls outside the legally applicable meaning of "about." A concentration change alone would not necessarily avoid infringement under the doctrine of equivalents, although the doctrine is fact-specific and constrained by prosecution history and claim scope.

Excipient limitations

The claims require a specific combination of:

Sodium chloride.
Sodium citrate dihydrate.
Citric acid anhydrous.

The formulation claims are therefore vulnerable to design-around strategies using another buffer system, a different citrate ratio, or a materially different tonicity agent. A formulation with the same active ingredient and pH but without the claimed citrate and citric-acid combination would present a stronger noninfringement position.

pH and osmolality limitations

The pH requirement is 5.5-6.5 across the principal formulations. The osmolality ranges differ:

250-310 mOsmol/kg for the higher-strength formulation.
255-345 mOsmol/kg for the lower-strength formulation.

These parameters create additional claim limitations. A product outside both the stated pH and osmolality ranges would be less likely to fall within the literal composition claims, provided the measured values are reliable and the claim language is construed as requiring those ranges.

What do the intravenous treatment claims cover?

Claims 5 and 6 require:

A patient.
Inhibition of platelet aggregation.
Intravenous treatment.
A pharmaceutically effective amount.
Use of the composition recited in claim 1 or claim 2.

These claims are narrower than a general method-of-use claim for tirofiban. They do not expressly cover every route of administration, every tirofiban dosage, or every tirofiban formulation. They are tied to the two specified compositions.

Because claims 5 and 6 depend on claims 1 and 2, a method practitioner would generally need to establish that the administered formulation satisfies the underlying composition limitations. A hospital's use of an already approved formulation could theoretically implicate a method claim, but the patent's expiration removes current US patent liability under these claims.

When did US Patent 5,965,581 expire?

US Patent 5,965,581 issued on October 12, 1999. The patent is an early US patent governed by the 20-year patent-term framework measured from the relevant nonprovisional filing date, subject to patent-term adjustment and any applicable extension.

Public patent records identify the patent as expired. The formulation patent therefore does not currently block manufacture, FDA approval, sale, or use of a tirofiban injection product in the United States. [2]

Exclusivity timeline

Event	Date or status
US patent application	Filed before issuance
Patent issuance	October 12, 1999
FDA approval of Aggrastat	1998
US Patent 5,965,581	Expired
Current patent barrier	None from this patent
Current regulatory pathway	ANDA or other applicable abbreviated pathway for a qualifying generic

The exact terminal date should be taken from the USPTO patent record and current Orange Book data for any transaction or litigation opinion. Expiration status, however, is dispositive for the present competitive analysis. [2, 3]

What is the Orange Book status of tirofiban and Aggrastat?

The FDA Orange Book historically listed US Patent 5,965,581 in connection with the Aggrastat reference product. Orange Book listing does not extend an expired patent. A listed patent can create an ANDA certification obligation while enforceable, but expiration removes the practical Paragraph IV litigation risk associated with that patent.

The Orange Book analysis should distinguish:

Product listing.
Patent listing.
Patent expiration.
Regulatory exclusivity.
Current reference-product status.

Tirofiban is a small molecule, not a biologic. Biosimilar procedures under the Public Health Service Act do not apply. A competing product would ordinarily proceed through the generic drug framework, including an abbreviated new drug application where the product and route qualify. [3, 4]

Are there current Paragraph IV challenges to US Patent 5,965,581?

No current Paragraph IV challenge to this patent creates a meaningful market barrier because the patent has expired.

Historically, an ANDA applicant seeking approval before patent expiration could have filed:

Paragraph III certification, agreeing to await expiration.
Paragraph IV certification, asserting that the patent was invalid, unenforceable, or not infringed.
A section viii statement, where an approved use was carved out and the patent did not cover the remaining labeling.

For an expired formulation patent, the Paragraph IV controversy is no longer commercially material. The principal approval issue is product equivalence and compliance with FDA requirements, not patent certification strategy.

Which companies challenged or competed with Aggrastat?

The competitive field includes the original sponsor, generic injectable manufacturers, and other antiplatelet products.

Company or product category	Role
Merck and associated Aggrastat commercialization entities	Original tirofiban sponsor and reference-product network
Generic injectable manufacturers	Potential ANDA applicants and suppliers of tirofiban hydrochloride injection
Eptifibatide manufacturers	Direct pharmacologic competitors in the GP IIb/IIIa class
Abciximab suppliers	Alternative GP IIb/IIIa inhibitor suppliers
Hospital and specialty injectable distributors	Commercial channels for institutional use

The relevant generic competition is product-specific. A company may avoid the expired patent while still facing FDA manufacturing requirements for sterile injectable production, validated analytical methods, container-closure integrity, particulate control, and aseptic processing.

What manufacturing and intellectual-property barriers remain?

Patent expiration does not eliminate technical barriers. Tirofiban injection is a sterile parenteral product, and the principal barriers include:

Sterile manufacturing

Manufacturers must demonstrate control of:

Aseptic filling.
Endotoxin levels.
Sterility.
Visible and subvisible particulate matter.
Container-closure integrity.
Hold times and batch uniformity.
Stability under labeled storage conditions.

Analytical characterization

The active ingredient and finished product require methods for:

Assay.
Related substances and degradation products.
Identity.
pH.
Osmolality.
Sterility and bacterial endotoxins.
Stability-indicating analysis.

Formulation execution

A competitor using the same or similar formulation must control citrate buffering, ionic strength, pH, and osmolality. Small changes may affect stability, tolerability, labeling, or bioequivalence strategy even if they do not create patent exposure.

Process and manufacturing patents

US Patent 5,965,581 does not appear, from the claims supplied, to cover a proprietary manufacturing process, container, delivery device, or broad pharmaceutical composition platform. Its claims are directed to the finished formulation and specified use. Separate process or device patents would require independent review and cannot be inferred from this patent alone.

How strong is the patent estate for tirofiban?

The current US estate is weak from an exclusionary standpoint because the principal formulation patent has expired.

Estate component	Assessment
Core molecule patent	Historical protection; expired
Formulation patent, US 5,965,581	Expired
Method-of-use claims in 5,965,581	Expired
Biosimilar protection	Not applicable
FDA exclusivity	No current exclusivity inferred from the expired patent
Generic entry risk	High from a patent perspective
Manufacturing risk	Moderate to high for sterile injectable production
Litigation risk	Low under this patent
Commercial substitution risk	Depends on FDA approval, supply, and institutional contracting

The patent’s historical value was concentrated in protecting a ready-to-use intravenous formulation and its use for platelet-aggregation inhibition. Its present value as a blocking right is zero in the United States because the patent term has ended.

What generic launch scenarios exist for tirofiban injection?

Three launch scenarios are commercially relevant.

Immediate post-expiration generic entry

A manufacturer with an approved ANDA can launch after patent expiration, subject to applicable regulatory requirements and any other enforceable exclusivity. This is the lowest patent-risk scenario.

Formulation-aligned generic entry

A generic manufacturer may use a formulation close to the disclosed composition, including tirofiban hydrochloride, sodium chloride, citrate, citric acid, pH 5.5-6.5, and the disclosed osmolality range. The expired patent does not prevent that approach.

Design-around formulation

A manufacturer may use a different buffer or concentration, provided the product remains pharmaceutically equivalent and acceptable to FDA. Design-around may reduce dependency on the exact historical formulation but can introduce formulation-development and stability risks.

How does tirofiban compare with competing platelet inhibitors?

Product	Active ingredient	Modality	Patent status relevant to this analysis
Aggrastat and generic tirofiban	Tirofiban hydrochloride	Small-molecule IV inhibitor	Principal cited formulation patent expired
Integrilin and generic eptifibatide	Eptifibatide	Peptide-like IV inhibitor	Separate patent and regulatory history
ReoPro	Abciximab	Monoclonal antibody fragment	Biologic-related regulatory and manufacturing framework
Oral P2Y12 inhibitors	Clopidogrel, prasugrel, ticagrelor	Oral antiplatelet agents	Different mechanisms, dosage forms, and patent estates

Tirofiban competes in a hospital-based intravenous market. Its commercial position depends on procedure volume, institutional protocols, dosing convenience, inventory requirements, and generic pricing. Oral antiplatelet drugs are not direct formulation substitutes but affect the broader antithrombotic treatment market.

What revenue exposure is associated with the expired patent?

The patent no longer protects revenue directly. Any historical revenue associated with Aggrastat was exposed to generic entry once the patent and applicable exclusivity periods ended.

Revenue exposure should be assessed through:

Reference-product unit sales.
Hospital purchasing contracts.
Generic price erosion.
Number of approved suppliers.
Shortages or discontinuations.
Use in PCI and acute coronary syndrome protocols.
Availability of alternative GP IIb/IIIa inhibitors.

Because tirofiban is an institutional injectable, generic price erosion can be substantial once multiple suppliers qualify, but supply concentration can preserve pricing temporarily. The patent itself does not justify a current exclusivity premium.

What is the geographic coverage of US Patent 5,965,581?

US Patent 5,965,581 provides protection only in the United States. It does not establish rights in Europe, Canada, Japan, China, or other jurisdictions.

International protection would require separate national or regional patents, such as European Patent Office filings or national applications. The US patent number cannot be used to infer foreign validity, expiration, or enforceability. Any global launch assessment requires a separate family-level review of priority filings, continuations, national-phase applications, terminal disclaimers, and local patent-term adjustments.

Key Takeaways

US Patent 5,965,581 covers narrow tirofiban intravenous formulations and related platelet-aggregation treatment methods.
The central limitations are tirofiban concentration, sodium chloride, citrate, citric acid, pH, and osmolality.
Claims 1, 2, 7, and 8 are composition claims; claims 5 and 6 are intravenous method claims.
The patent does not broadly cover all tirofiban products or all antiplatelet therapies.
The patent has expired and does not currently block US generic entry.
Tirofiban is a small molecule, so biosimilar regulation does not apply.
Current entry barriers are primarily FDA approval, sterile manufacturing, analytical control, supply reliability, and institutional contracting.
Any current freedom-to-operate opinion should review the full US patent family and separate patents covering manufacturing, containers, dosing regimens, and commercial products.

Frequently Asked Questions

Does US Patent 5,965,581 cover tirofiban hydrochloride injection?

Yes. Claims 3, 4, 7, and 8 expressly recite tirofiban hydrochloride monohydrate formulations. Claims 1 and 2 recite corresponding free-acid concentrations.

Can a generic company use the same tirofiban formulation after patent expiration?

Yes. Patent expiration removes the patent-based restriction, subject to FDA approval, applicable regulatory requirements, and any separate unexpired patent or exclusivity right.

Is tirofiban subject to a biosimilar pathway?

No. Tirofiban is a synthetic small molecule. A qualifying generic tirofiban injection would generally use the ANDA framework rather than the biosimilar pathway.

Could a different buffer avoid the patent claims?

Potentially. The claims require sodium citrate dihydrate and citric acid anhydrous at specified approximate concentrations. A materially different buffer system may avoid literal infringement, although product quality and regulatory equivalence would remain separate issues.

Does the patent cover oral tirofiban or subcutaneous tirofiban?

No. The supplied claims are directed to intravenous compositions and intravenous platelet-aggregation treatment. They do not broadly claim oral or subcutaneous dosage forms.

References

U.S. Food and Drug Administration. (2024). Aggrastat (tirofiban hydrochloride) injection prescribing information.
United States Patent and Trademark Office. (1999). U.S. Patent No. 5,965,581: Pharmaceutical compositions containing tirofiban.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application guidance and generic drug regulatory framework.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	004223	⤷ Start Trial
Austria	213648	⤷ Start Trial
Australia	712755	⤷ Start Trial
Australia	7718996	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 5,965,581