United States Patent 4,665,062: Claim Scope, Expiration, and Foscarnet Patent Landscape

U.S. Patent No. 4,665,062 covers human and veterinary pharmaceutical preparations containing phosphonoformic acid, also known as foscarnet, or a physiologically acceptable salt. Its principal protection is formulation-based rather than compound-based. The claims require a defined concentration range, a pharmaceutical carrier suitable for human administration, and, for certain claims, a topical dosage form.

The patent issued on May 12, 1987. Under the pre-Uruguay Round patent term applicable to the patent, its ordinary 17-year term from issuance ended on May 12, 2004, absent an unusual term adjustment or extension. The patent therefore no longer creates a current U.S. patent barrier to generic foscarnet products. FDA regulatory exclusivity and patent rights are separate rights; any regulatory exclusivity associated with the original Foscavir approval also expired long ago.[1-4]

What drug does U.S. Patent 4,665,062 protect?

U.S. Patent 4,665,062 protects pharmaceutical preparations containing phosphonoformic acid or an acceptable salt, particularly the tri-sodium salt of phosphonoformic acid.

The active ingredient is foscarnet, generally administered clinically as foscarnet sodium, commonly identified as trisodium phosphonoformate or trisodium phosphonoformate hexahydrate. Foscarnet is an inorganic pyrophosphate analogue used against certain herpesviruses and human cytomegalovirus, particularly in patients with resistant infection or intolerance to other antiviral treatments.[1]

The patent does not broadly claim every use of foscarnet or the chemical compound itself. Its claims are directed to pharmaceutical preparations that contain the compound within a specified concentration range and that meet carrier, sterility, or dosage-form requirements.

Patent identification

Item	Data
Patent	U.S. Patent No. 4,665,062
Issue date	May 12, 1987
Subject matter	Pharmaceutical preparations containing phosphonoformic acid
Active ingredient	Phosphonoformic acid or physiologically acceptable salt
Specifically recited salt	Tri-sodium salt of phosphonoformic acid
Concentration range	About 0.05% to about 20% by weight
Covered routes	Topical administration under claims 1, 4, and 6; broader human administration under claims 2 and 3
Patent term	Ordinarily expired May 12, 2004
Current blocking effect	None based on the expired patent

What are the independent claims in U.S. Patent 4,665,062?

Claims 1 and 2 are the principal independent claims.

Claim 1: topical preparation

Claim 1 covers a pharmaceutical preparation:

Effective for treating viral infections in animals or humans;
Packaged in dosage-unit form;
Suitable for topical administration to humans;
Containing approximately 0.05% to 20% by weight of phosphonoformic acid or an acceptable salt; and
Using a physiologically acceptable carrier substantially free of pharmaceutically unacceptable impurities.

This is a combination claim. A product must satisfy the active-ingredient, concentration, dosage-form, topical-use, and carrier limitations to fall within its literal scope.

The claim does not require a particular topical dosage form. That limitation appears in dependent claim 4, which identifies solutions, ointments, gels, suspensions, and creams.

Claim 2: sterile human-use preparation

Claim 2 covers a preparation:

Effective for treating viral infections in animals or humans;
In dosage-unit form;
Containing approximately 0.05% to 20% by weight of the claimed compound or salt; and
Containing a physiologically acceptable sterile carrier suitable for human administration.

Claim 2 is broader in route than claim 1 because it does not expressly require topical administration. Its central additional limitation is sterility. This claim is the provision most relevant to an injectable or otherwise sterile human product, although the claim language does not expressly recite injection.

How do claims 3 through 6 narrow the patent?

Claims 3 through 6 add salt, dosage-form, and formulation limitations.

Claim	Limitation	Practical scope
1	Topical dosage-unit preparation; 0.05% to 20% active; acceptable carrier	Broad topical composition claim
2	Sterile dosage-unit preparation; 0.05% to 20% active; sterile carrier	Broad sterile human-use composition claim
3	Claim 2, where compound is tri-sodium phosphonoformate	Sterile preparation specifically containing foscarnet sodium
4	Claim 1, where preparation is solution, ointment, gel, suspension, or cream	Enumerated topical dosage forms
5	Claim 4, where preparation is a cream containing an absorption promoter	Narrow topical cream claim
6	Claim 1 or 4, where compound is tri-sodium phosphonoformate	Topical foscarnet sodium preparations

Claim 3 and injectable foscarnet

Claim 3 is the most commercially relevant claim for a sterile foscarnet sodium product because it combines claim 2's sterile-carrier requirement with the specifically identified tri-sodium salt.

The claim does not expressly require:

A particular injection route;
A particular concentration other than the 0.05% to 20% range;
A particular pH;
A particular tonicity;
A particular container;
A particular stabilizer;
A particular dosage volume; or
A particular crystallographic or hydration state.

Those omissions limit the claim's technical specificity. At the same time, its concentration and sterility requirements could have captured a wide range of sterile human formulations during the patent term.

Claim 5 and absorption promoters

Claim 5 is limited to a cream that contains an absorption promoter. The patent does not, in the claim text provided, identify a closed list of absorption promoters. The scope would therefore depend on the specification's disclosure and on how a court construes the term in light of that disclosure.

A topical product that contains foscarnet sodium but is not a cream would not meet claim 5. A cream without an absorption promoter would also fall outside claim 5, although it could still implicate claims 1, 4, or 6 if the other limitations were satisfied.

What formulations are protected by U.S. Patent 4,665,062?

The patent covers two principal formulation categories: topical preparations and sterile preparations for human administration.

Topical formulations

Claims 1, 4, and 6 reach formulations such as:

Solutions;
Ointments;
Gels;
Suspensions; and
Creams.

The active concentration must be approximately 0.05% to 20% by weight. A topical product outside that concentration range would not literally meet the concentration limitation, subject to claim-construction principles concerning the terms "about."

The topical claims also require a carrier suitable for human use. A laboratory vehicle, industrial solvent, or carrier containing pharmaceutically unacceptable impurities would not satisfy the express carrier limitation.

Sterile formulations

Claims 2 and 3 reach sterile preparations containing the active ingredient within the same approximate concentration range. Claim 3 is restricted to the tri-sodium salt.

For a sterile foscarnet sodium formulation, the central technical issues would include:

Whether the product contains the claimed salt;
Whether the active concentration falls within the claimed range;
Whether the product is in dosage-unit form;
Whether the carrier is sterile;
Whether the carrier is physiologically acceptable; and
Whether the product is suitable for human administration.

What the patent does not expressly claim

The supplied claims do not expressly claim:

Foscarnet as a chemical compound in isolation;
A method of treating a named viral disease;
A specific viral target such as CMV, HSV, or HIV;
A specific intravenous dosing regimen;
A particular infusion rate;
A specific pH or buffer system;
A particular container-closure system;
A manufacturing process;
A crystalline form;
A polymorph;
A prodrug;
A combination with another antiviral; or
A diagnostic method.

That distinction matters. The patent could have covered a formulation product during its term, but it did not create a perpetual monopoly over foscarnet chemistry or every foscarnet treatment method.

When did U.S. Patent 4,665,062 expire?

The patent's ordinary term ended on May 12, 2004.

For patents issued before June 8, 1995, the applicable U.S. term generally was 17 years from grant, subject to statutory adjustments and possible patent-term extension. U.S. Patent 4,665,062 issued on May 12, 1987, producing an ordinary expiration date of May 12, 2004.[2]

No current patent-rights analysis should treat the patent as an enforceable barrier unless a separate and unusual post-issuance right existed. The patent number itself does not establish a live patent claim after expiration.

Exclusivity timeline

Event	Date or period
Patent issued	May 12, 1987
Ordinary 17-year patent term	May 12, 1987 to May 12, 2004
Foscavir FDA approval	1991
Orphan-drug exclusivity associated with the original approval	Approximately seven years from approval, subject to FDA regulatory records
Patent expiration	May 12, 2004
Current patent blocking effect	Expired

Orphan-drug exclusivity is product- and indication-specific. It does not extend the patent term and does not prevent all future approvals outside the protected indication.[3]

What is the Orange Book status of foscarnet and Foscavir?

The Orange Book identifies approved drug products and, where applicable, patent and exclusivity information submitted for listed products. A listed patent must be evaluated by product, NDA, dosage form, and the current Orange Book entry rather than by searching the patent number alone.[4]

U.S. Patent 4,665,062 is expired and cannot currently support a Paragraph IV challenge against a new ANDA. A generic applicant would not need to certify Paragraph IV to an expired patent. If the patent were listed during an earlier period, an ANDA applicant could have used a certification addressing expiration or invalidity, but that historical procedural question does not revive the patent.

The current commercial significance of Foscavir therefore depends primarily on:

FDA approval requirements;
Product-specific quality and manufacturing controls;
Supply of foscarnet sodium;
Labeling and clinical evidence;
Any later patents not covered by Patent No. 4,665,062; and
Market and procurement conditions.

How strong was the patent estate for foscarnet?

The patent was moderately broad as a formulation patent but weak as a long-term platform estate.

Strengths during the patent term

The patent had several commercially useful features:

A concentration range spanning low-strength topical products and higher-strength sterile products;
Coverage of both topical and sterile preparations;
Express coverage of the tri-sodium salt;
Coverage of multiple topical dosage forms;
Carrier-quality and sterility limitations directed to human pharmaceutical products;
Potential applicability to an injectable formulation without requiring a specific injection route.

Limitations

The estate had important weaknesses:

It did not claim foscarnet chemistry generally.
It did not claim a specific approved treatment regimen.
It did not identify a narrow formulation architecture such as a particular buffer, pH, excipient, or container.
The "about" concentration language may create claim-construction questions at the boundaries.
The claims require multiple formulation characteristics, creating potential noninfringement positions.
The patent expired in 2004.

The patent's commercial value would have been greatest against a product using the tri-sodium salt at a covered concentration in a sterile human formulation or in one of the specified topical forms. Its value would have been substantially lower against a product outside the claimed concentration, using a different active form, or failing the carrier and dosage-unit requirements.

Did U.S. Patent 4,665,062 cover the marketed intravenous Foscavir product?

Claim 3 is the principal claim that could have been relevant to a sterile foscarnet sodium product during the patent term. Foscavir is an intravenous foscarnet sodium product used for CMV retinitis in immunocompromised patients and for acyclovir-resistant mucocutaneous HSV infections in immunocompromised patients.[1]

The supplied claims alone do not establish infringement by the marketed product. Infringement would require comparison of the approved formulation and manufacturing specifications with each claim limitation. Relevant facts would include the exact salt form, concentration, dosage-unit presentation, carrier, sterility status, and human-use labeling.

A claim chart based only on the claim language produces the following assessment:

Claim limitation	Likely relevance to an injectable foscarnet sodium product
Phosphonoformic acid or physiologically acceptable salt	Likely relevant
Tri-sodium salt	Directly relevant under claim 3
0.05% to 20% by weight	Requires formulation-specific comparison
Dosage-unit form	Requires product and presentation analysis
Sterile carrier	Likely relevant
Physiologically acceptable carrier	Likely relevant
Suitable for human administration	Likely relevant
Topical administration	Not required by claim 3

This is a historical infringement analysis only. The patent's expiration eliminates present enforcement risk under this patent.

Were there Paragraph IV challenges to U.S. Patent 4,665,062?

A current Paragraph IV challenge to Patent No. 4,665,062 is not commercially meaningful because the patent expired in 2004.

Paragraph IV litigation applies when an ANDA applicant certifies that a listed patent is invalid, unenforceable, or will not be infringed. A patent that has expired does not create a continuing patent exclusion period. The relevant generic strategy would instead involve an ANDA or another applicable FDA pathway, subject to any currently listed patents or exclusivities associated with the reference product.[5]

The supplied record does not establish a reported Paragraph IV case specifically directed to this patent. No litigation conclusion should be drawn from the patent claims alone.

Which companies are challenging foscarnet exclusivity?

The relevant competitive group includes:

The holder or marketer of the Foscavir reference product;
Potential ANDA applicants seeking approval for foscarnet sodium injection;
Contract manufacturers capable of producing sterile foscarnet sodium;
Hospital and specialty-pharmacy suppliers; and
Suppliers of active pharmaceutical ingredient and sterile finished product.

The expired patent does not identify a current challenger, settlement, or license. It also does not establish that a specific company has filed an ANDA or litigated against the reference product.

A competitive analysis must separate patent challenges from commercial entry. A company may enter after patent expiration without filing a Paragraph IV challenge if no unexpired listed patent blocks approval. Conversely, manufacturing complexity can delay entry even where patent barriers are absent.

What manufacturing and intellectual-property barriers remain?

Foscarnet sodium is a relatively specialized sterile product. The principal barriers are more likely to be regulatory, manufacturing, and commercial than patent-based.

Manufacturing barriers

Potential barriers include:

Reliable sourcing of pharmaceutical-grade foscarnet sodium;
Control of elemental impurities and residual contaminants;
Sterile processing and aseptic filling;
Control of solution stability;
Container-closure compatibility;
Validation of sterilization and filtration processes;
Control of pH, osmolality, and particulate matter; and
Demonstration of consistent product quality.

The original patent claims require a carrier substantially free of pharmaceutically unacceptable impurities. That language reflects a pharmaceutical-quality requirement, but it does not create a current manufacturing monopoly.

Regulatory barriers

A generic injectable product generally requires substantial chemistry, manufacturing, and controls data. Depending on the reference product and FDA determination, the applicant may also need to address:

Product sameness;
Strength and dosage form;
Route of administration;
Inactive ingredients;
Sterility assurance;
Labeling;
Packaging; and
Demonstration of bioequivalence or other applicable requirements.

These requirements can be material even when no enforceable patent remains.

How does this patent compare with a modern formulation patent?

Patent No. 4,665,062 is an early formulation patent with broad functional and compositional language. A modern formulation patent often claims a narrower technical combination, such as:

A defined pH window;
A specified buffer;
A particular concentration and osmolality;
A stabilizer system;
A lyophilized presentation;
A container-closure configuration;
A dosing regimen; or
A manufacturing process.

The 1987 patent has broader potential coverage across dosage forms, but less technical precision. Modern patents often have narrower literal scope but may be harder to design around if they are tied to a commercially necessary product architecture.

What generic launch risks exist for foscarnet products?

For a new U.S. foscarnet sodium product, the expired patent creates no present launch risk. The principal risks are:

FDA approval risk for the sterile injectable product;
Product-quality and stability risk;
Supply-chain risk for active ingredient and sterile manufacturing;
Commercial risk from a limited but specialized antiviral market;
Potential later patent or regulatory exclusivity issues associated with a particular reference product; and
Litigation risk unrelated to U.S. Patent 4,665,062.

A generic manufacturer would normally assess current Orange Book listings, FDA approvals, reference-product requirements, and any later patents before selecting an ANDA strategy.[4-5]

What is the geographic coverage of U.S. Patent 4,665,062?

The patent provides rights only in the United States. It does not establish protection in Europe, Japan, Canada, Australia, or other jurisdictions.

Foreign counterparts, if any, would require separate analysis of:

National filing dates;
Grant status;
Patent term;
Supplementary protection certificates;
Opposition or revocation proceedings;
Local claim amendments; and
National expiration dates.

The U.S. expiration date cannot be used to infer foreign expiration dates.

Key Takeaways

U.S. Patent 4,665,062 is a formulation patent covering phosphonoformic acid, particularly foscarnet sodium.
The claims require approximately 0.05% to 20% active ingredient by weight.
Claims 1, 4, and 6 focus on topical products, including solutions, ointments, gels, suspensions, and creams.
Claims 2 and 3 cover sterile human-use preparations, with claim 3 specifically reciting the tri-sodium salt.
The patent does not broadly claim foscarnet chemistry, a named antiviral indication, or every foscarnet treatment method.
The patent issued May 12, 1987 and ordinarily expired May 12, 2004.
It is not a current U.S. patent barrier to generic foscarnet.
Any current entry analysis must focus on FDA requirements, Orange Book status, later patents, sterile manufacturing, supply, and market economics.
The patent's historical strength was greatest against sterile foscarnet sodium formulations and covered topical products during the patent term.
The patent provides no basis for conclusions about current litigation, settlements, licenses, or ANDA filings without separate docket and FDA-record analysis.

FAQs

Is foscarnet sodium still protected by U.S. Patent 4,665,062?

No. U.S. Patent 4,665,062 ordinarily expired on May 12, 2004.

Does Patent 4,665,062 claim Foscavir by brand name?

No. The claims cover pharmaceutical preparations containing phosphonoformic acid or its salts. They do not claim the Foscavir trademark.

Does the patent cover topical foscarnet cream?

Historically, claim 6 could cover a topical cream containing tri-sodium phosphonoformate within the claimed concentration range. Claim 5 adds the requirement for an absorption promoter.

Could a generic applicant still file a Paragraph IV certification to this patent?

A Paragraph IV certification is not a meaningful current barrier for an expired patent. The applicant must evaluate the patents currently listed for the applicable reference product.

Does expiration of the U.S. patent end all foscarnet exclusivity worldwide?

No. U.S. patent expiration affects only U.S. patent rights. Foreign patents, regulatory exclusivities, trademarks, manufacturing know-how, and market-specific requirements are separate matters.

References

U.S. Food and Drug Administration. (n.d.). Foscavir (foscarnet sodium) injection prescribing information.
U.S. Patent No. 4,665,062. (1987). Pharmaceutical preparations containing phosphonoformic acid. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Orphan drug designation and exclusivity.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book.
U.S. Food and Drug Administration. (n.d.). ANDA submissions: Patent certification and 30-month stay provisions.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Sweden	7607496	Jul 1, 1976

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	369014	⤷ Start Trial
Austria	A465477	⤷ Start Trial
Australia	2650577	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 4,665,062