United States Patent 4,215,113: Scope, Claims, Expiration, and Foscarnet Patent Landscape

U.S. Patent No. 4,215,113 covers the use of phosphonoformic acid, also known as foscarnet, and its physiologically acceptable salts to treat viral infections. The patent claims extend across herpesviruses, influenza viruses, papillomaviruses, and specified clinical conditions. Its legal term expired in 1997, so the claims no longer create an enforceable barrier to generic manufacture, marketing, formulation, or clinical use in the United States.

The patent remains relevant as an early foundational patent for foscarnet, but it has no current blocking value. Modern commercial protection for foscarnet would have to arise from later patents covering a formulation, manufacturing process, delivery system, combination therapy, or newly approved method of use.

What does U.S. Patent 4,215,113 cover?

U.S. Patent 4,215,113 covers therapeutic administration of phosphonoformic acid or a physiologically acceptable salt to an infected human or animal host.[1]

The principal claim is Claim 1:

A method for the selective treatment of virus infections in an animal or human host comprising administering to said host so infected an amount effective to treat said virus infection of phosphonoformic acid or a physiologically acceptable salt thereof.

The patent is therefore a method-of-treatment patent. It does not principally claim:

Foscarnet sodium as a new chemical compound;
a particular injectable composition;
a specific dosage regimen;
a manufacturing process;
a pharmaceutical container or delivery device;
a diagnostic method;
a combination treatment with another antiviral.

The protected product is commonly identified as foscarnet or foscarnet sodium. Foscarnet sodium is the injectable salt used in the FDA-approved product Foscavir.

What is the scope of Claim 1?

Claim 1 has four central elements:

Claim element	Scope
Subject	An animal or human host
Condition	A virus infection
Active agent	Phosphonoformic acid or a physiologically acceptable salt
Conduct	Administration of an amount effective to treat the infection

The claim is broad because it does not limit the treatment to a named virus, dose, route, formulation, disease stage, or patient population. The phrase "selective treatment" appears in the claim but is not tied to a specific selectivity ratio, mechanism, or assay in the claim language supplied.

The claim requires actual administration to an infected host. It would not ordinarily cover the isolated compound, a composition sitting on a shelf, or an in vitro assay standing alone. Those activities might implicate other patent claims in a different patent, but they are outside the direct language of this claim.

The claim also requires an "amount effective to treat" the viral infection. That limitation links infringement to therapeutic administration rather than incidental exposure. It may create factual disputes over whether the administered amount was intended and capable of treating the claimed infection.

How do Claims 2 through 16 narrow the patent?

Claims 2 through 16 depend on Claim 1. They do not replace the basic requirement to administer phosphonoformic acid or a physiologically acceptable salt. Each claim narrows the infection or disease being treated.

Claim	Claimed target
1	Viral infections generally
2	Herpesvirus infections
3	Herpes simplex virus type 1
4	Herpes simplex virus type 2
5	Varicella, identified in the patent as herpes zoster
6	Cytomegalovirus
7	Epstein-Barr virus
8	Influenza viruses
9	Influenza A or B
10	Influenza A
11	Papillomavirus infections
12	Herpes dermatitis, herpes genitalis, herpes keratitis, and herpes encephalitis
13	Herpes zoster
14	Infectious mononucleosis
15	Influenza
16	Warts

The dependent structure matters. A party practicing a method for CMV treatment would potentially fall within Claim 6 only if all elements of Claim 1 were also met. A method for treating warts would implicate Claim 16, subject to the underlying elements of Claim 1.

Claims 5 and 13 overlap substantially because both address varicella-zoster-related disease. Claim 13 identifies herpes zoster as the clinical condition, while Claim 5 uses the viral classification language in the supplied claim set. Claims 8 through 10 create a descending influenza hierarchy, with Claim 10 being limited to influenza A.

What does Claim 17 protect?

Claim 17 covers topical administration of phosphonoformic acid or a physiologically acceptable salt:

A method according to claim 1, comprising topical administration of phosphonoformic acid or a physiologically acceptable salt thereof.

This claim is narrower than Claim 1 because it requires topical administration. It does not claim every topical formulation as a composition. It claims the act of treating a viral infection through topical administration.

The claim could potentially reach topical use for conditions such as herpes dermatitis, herpes genitalis, herpes keratitis, or viral warts, depending on the treatment facts and claim construction. It does not specify:

cream, gel, ointment, lotion, solution, or patch;
concentration;
excipients;
penetration enhancer;
dosing frequency;
treatment duration;
anatomical application site.

A later topical formulation patent could have coexisted with Claim 17 during the patent term if it claimed a novel composition or formulation. Such a later patent would not extend the term of U.S. Patent 4,215,113.

When did U.S. Patent 4,215,113 expire?

U.S. Patent 4,215,113 issued on July 29, 1980.[1] Because it belongs to the pre-Uruguay Round patent term regime, its ordinary U.S. term was 17 years from grant. The patent therefore expired on July 29, 1997, assuming no earlier terminal disclaimer or other term-ending event.

Event	Date
U.S. patent grant	July 29, 1980
Ordinary pre-1995 patent term	17 years from grant
Estimated expiration	July 29, 1997
Current enforceability	None after expiration

The patent predates the 20-year-from-earliest-effective-filing-date system established by the Uruguay Round Agreements Act. Patent term adjustment and patent term extension rules associated with later-issued patents do not revive this expired patent.

What is the FDA status of foscarnet?

The FDA approved Foscavir, an intravenous foscarnet sodium product, for treatment of cytomegalovirus retinitis in patients with AIDS and for treatment of acyclovir-resistant mucocutaneous herpes simplex infections in immunocompromised patients.[2]

The FDA-approved use is narrower than the full claim set of U.S. Patent 4,215,113. The patent claims reach influenza, papillomavirus, Epstein-Barr virus, herpes simplex, varicella-zoster virus, CMV, and several clinical conditions. The approved Foscavir labeling centers on CMV retinitis and acyclovir-resistant mucocutaneous HSV.

Regulatory issue	Status
Active ingredient	Foscarnet sodium
Brand	Foscavir
Route	Intravenous infusion
FDA status	Approved drug
Primary approved uses	CMV retinitis; acyclovir-resistant mucocutaneous HSV in immunocompromised patients
Patent 4,215,113	Expired
Biosimilar pathway	Not applicable to this small-molecule drug

Foscarnet is a small molecule, not a biologic. Biosimilar provisions under section 351(k) of the Public Health Service Act therefore do not apply. A competing product would generally use an abbreviated new drug application, a full new drug application, or another applicable FDA pathway rather than a biosimilar application.

What is the Orange Book status of foscarnet?

The Orange Book lists FDA-approved drug products and, where applicable, patent and regulatory exclusivity information.[3] An expired foundational method patent cannot support a current Orange Book patent block.

For an approved foscarnet sodium product, the commercially relevant questions are whether a current product sponsor has listed an unexpired patent covering the approved product, its formulation, or an approved method of use. U.S. Patent 4,215,113 itself cannot function as a current Orange Book barrier because its term ended in 1997.

Any ANDA applicant addressing a currently listed unexpired patent could face a Paragraph IV certification. The expired status of Patent 4,215,113 means that a Paragraph IV challenge to this patent is no longer commercially necessary. A generic applicant would instead evaluate any later-listed patents, regulatory exclusivity, labeling requirements, and FDA bioequivalence issues.

Were there Paragraph IV challenges or litigation involving this patent?

There is no current Paragraph IV risk associated with U.S. Patent 4,215,113 because the patent expired more than two decades ago. A Paragraph IV certification is directed to a listed patent that the applicant asserts is invalid, unenforceable, or not infringed. An expired patent cannot delay approval through the ordinary Hatch-Waxman 30-month stay mechanism.[4]

The patent record supplied does not establish a material modern infringement action involving this patent. The existence of historical patent litigation cannot be inferred solely from the claim text. Any current dispute involving foscarnet would more likely concern:

a later injectable formulation;
a manufacturing or purification process;
a dosing regimen;
a new indication;
a combination therapy;
a device or administration system;
regulatory exclusivity or labeling.

The absence of a current enforceable patent does not prevent litigation over trade secrets, product quality, regulatory substitution, contract rights, or later patents.

What formulations are protected by the patent?

U.S. Patent 4,215,113 does not, based on the supplied claims, claim a specific pharmaceutical formulation. Claim 17 claims topical administration as a therapeutic method, not a particular topical composition.

The patent does not identify claim limitations directed to:

foscarnet sodium concentration;
pH;
buffer system;
tonicity agent;
infusion rate;
sterile packaging;
preservative;
excipient;
container closure;
stability profile.

The FDA product is administered intravenously and requires renal-function-based dosing and monitoring because foscarnet has clinically significant nephrotoxicity and electrolyte-related risks.[2] Those product characteristics may create technical and regulatory barriers for a generic manufacturer, but they do not extend the expired patent.

How strong was the patent estate?

The patent had broad historical subject-matter coverage but limited claim-type diversity.

Strength	Assessment
Therapeutic breadth	Broad virus and host language in Claim 1
Specific disease coverage	Extensive dependent claims
Route coverage	Broad in Claim 1; topical route expressly claimed in Claim 17
Composition protection	Not apparent from supplied claims
Manufacturing protection	Not apparent from supplied claims
Dosage protection	Not expressly claimed
Current legal strength	None, because the patent expired
Historical design-around difficulty	Moderate to high for therapeutic use during the term
Present commercial blocking value	Zero

During its term, Claim 1 could have presented a broad barrier to therapeutic use of foscarnet across multiple viral diseases. The broad language also could have raised validity questions involving enablement, written description, utility, and the scope of the disclosed antiviral activity. Those questions would have mattered only during the enforceable term.

The patent did not create a continuing monopoly over foscarnet as a chemical entity. A company that manufactured or sold foscarnet for non-therapeutic purposes would not necessarily practice the method claim. Product liability, regulatory, or later-patent issues could still apply, but they are separate from this patent.

How does foscarnet compare with competing antiviral patent estates?

Drug	Primary use area	Product type	Patent risk relative to U.S. 4,215,113
Foscarnet	CMV and resistant HSV	Small molecule, intravenous	Foundational patent expired
Acyclovir	HSV and varicella-zoster	Small molecule	Original compound and use protections expired; later formulations may differ
Ganciclovir	CMV	Small molecule	Later-generation product and formulation patents
Cidofovir	CMV and other DNA viruses	Small molecule	Later compound, formulation, and use patents
Brincidofovir	CMV and other DNA viruses	Small molecule prodrug	Later product and method patents
Letermovir	CMV prophylaxis	Small molecule	Separate, later patent estate
Oseltamivir	Influenza	Small molecule	Separate influenza antiviral estate
Baloxavir	Influenza	Small molecule	Separate, later compound and use estate

Foscarnet’s principal commercial disadvantage is its intravenous administration and toxicity monitoring burden. Its main clinical value is activity against selected resistant herpesviruses, particularly when acyclovir or ganciclovir resistance limits alternatives.[2]

What generic launch risks exist for foscarnet?

The expired patent removes the principal historical patent barrier. A generic entrant would still face:

FDA quality and chemistry requirements for foscarnet sodium.
Sterile injectable manufacturing and container-closure validation.
Demonstration of pharmaceutical equivalence and bioequivalence under the applicable FDA pathway.
Labeling consistency with the reference product.
Renal dosing and electrolyte-monitoring requirements.
Potential later patents listed for a particular reference product.
Commercial limits from a small, specialized market.
Supply-chain and active pharmaceutical ingredient qualification issues.

No biosimilar risk exists because foscarnet is not a biologic. The primary competitive threat is from generic injectable foscarnet sodium and from substitute antiviral products, rather than from biosimilar competition.

What licensing deals affect U.S. Patent 4,215,113?

The patent itself does not establish a current license, royalty, or field-of-use restriction. A historical license may have supported development or commercialization, but licensing rights do not survive as a patent-based market exclusion after patent expiration unless a separate contract, trade-secret right, or later patent remains in force.

The Foscavir commercial history involved rights and marketing arrangements separate from the expired patent. Those arrangements must be analyzed through transaction documents, FDA sponsor records, and company disclosures rather than inferred from U.S. Patent 4,215,113.

What is the current geographic coverage?

U.S. Patent 4,215,113 covered the United States only. Its expiration ended U.S. patent rights in 1997. Foreign counterparts, if any, required separate national analysis and may have had different filing dates, terms, prosecution histories, and expiration dates.

A current international freedom-to-operate review would need to examine:

European Patent Office records;
national European registers;
Canadian and Japanese patent records;
later foscarnet formulation patents;
manufacturing patents;
product-specific regulatory exclusivity;
active patents in countries where the product is manufactured or sold.

The U.S. patent cannot be used to block manufacture or sale outside the United States.

Key Takeaways

U.S. Patent 4,215,113 claims therapeutic administration of phosphonoformic acid or its physiologically acceptable salts.
Claim 1 is a broad antiviral method claim covering infected humans and animals.
Claims 2 through 16 narrow the method to named virus classes and clinical conditions.
Claim 17 specifically covers topical administration.
The patent issued July 29, 1980 and expired approximately July 29, 1997.
The patent does not appear from the supplied claims to protect a specific foscarnet composition, manufacturing process, dose, or device.
Foscarnet is a small molecule; biosimilar regulation does not apply.
The FDA-approved Foscavir indications are narrower than the patent's claimed viral scope.
No current Paragraph IV or Orange Book blocking position can arise from this expired patent.
Current commercial risk depends on later patents, injectable manufacturing capability, FDA requirements, supply, and the economics of the specialized antiviral market.

FAQs

Can a company market generic foscarnet without licensing U.S. Patent 4,215,113?

Yes. The patent expired in 1997, so it no longer requires a license for U.S. commercial activity.

Does U.S. Patent 4,215,113 cover foscarnet sodium as a chemical compound?

Not based on the supplied claims. The claims cover therapeutic use of phosphonoformic acid or its salts, not the compound as an unclaimed composition of matter.

Does Claim 17 cover every topical foscarnet product?

No. Claim 17 covers topical administration as a treatment method. It does not expressly claim every cream, gel, ointment, solution, or other topical composition.

Is foscarnet eligible for a biosimilar application?

No. Foscarnet is a small-molecule drug. A competing product would use an applicable small-molecule FDA pathway, generally an ANDA or NDA rather than a section 351(k) biosimilar application.

Could a later patent still block a generic foscarnet product?

Yes. A later patent could cover a formulation, manufacturing process, dosing regimen, delivery system, combination, or approved method of use. Such a patent would be separate from U.S. Patent 4,215,113 and would require an independent validity and infringement analysis.

References

United States Patent and Trademark Office. (1980). U.S. Patent No. 4,215,113: Antiviral use of phosphonoformic acid.
U.S. Food and Drug Administration. (2023). Foscavir (foscarnet sodium) injection prescribing information.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, Orange Book.
21 U.S.C. § 355(j); 35 U.S.C. § 271(e); 35 U.S.C. § 154.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Sweden	7607496	Jul 01, 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
Australia	510809	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,215,113

Summary for Patent: 4,215,113