United States Drug Patent 4,507,305: Acyclovir Composition, Treatment Claims, Expiration, and Patent Landscape

US Patent 4,507,305 covers pharmaceutical compositions and treatment methods using acyclovir, also identified in the claims as 9-(1,3-dihydroxy-2-propoxymethyl)guanine. The patent focuses on injectable compositions, oral administration, and topical administration for herpes-family viral infections. It expired in 2002 and no longer creates a blocking patent right for acyclovir products in the United States.

The patent has commercial importance as an early acyclovir use and formulation patent, but its claims are no longer enforceable. Current acyclovir competition is governed by generic drug approval requirements, manufacturing capability, product quality, and commercial positioning rather than by US Patent 4,507,305.

What drug does US Patent 4,507,305 protect?

US Patent 4,507,305 protects pharmaceutical use of acyclovir. The claim language uses the chemical description “9-(1,3-dihydroxy-2-propoxymethyl)guanine,” which corresponds to acyclovir, also known as acycloguanosine.

Acyclovir is a guanosine analogue active against herpes-family viruses. It is phosphorylated preferentially in infected cells and inhibits viral DNA polymerase after conversion to its active triphosphate form.

The patent covers:

Product or use	Covered by the supplied claims
Acyclovir active ingredient	Yes
Pharmaceutically acceptable acyclovir salts	Yes
Acyclovir sodium	Specifically yes
Injectable composition	Yes
Oral administration	Yes
Topical administration	Yes
HSV-1 treatment	Yes
HSV-2 treatment	Yes
Cytomegalovirus treatment	Yes, for injectable and oral claims
Epstein-Barr virus treatment	Yes, for injectable and oral claims
Varicella-zoster virus treatment	Yes
Specific dosage strength	No
Specific excipient system	No
Specific container or device	No
Specific manufacturing process	No

The claims do not cover every acyclovir product in identical terms. Injectable products must satisfy the composition requirements in claims 1-3, while oral and topical products are addressed through separate method claims.

What are the independent claims in US Patent 4,507,305?

The principal independent claims are claims 1, 4, 11, and 17.

Claim 1: injectable composition

Claim 1 requires:

An injectable pharmaceutical composition;
An effective amount of acyclovir or a pharmaceutically acceptable salt; and
A pharmaceutically acceptable carrier.

The claim is directed to the composition itself, not merely to a method of using it. A product would need to satisfy all three elements to fall within the literal scope of the claim.

The phrase “effective amount” is functional rather than numerical. The claim does not specify a concentration, dose, infusion rate, pH, tonicity agent, preservative, or container system.

Claim 4: injectable treatment method

Claim 4 covers treating a viral infection in a mammal by administering an effective amount of the composition of claim 1.

Because claim 4 depends on claim 1, it incorporates the injectable-composition limitations. A method using oral or topical acyclovir would not ordinarily satisfy claim 4 unless the administered product also met the injectable composition limitation.

Claim 11: oral treatment method

Claim 11 covers treating viral infection in a mammal by orally administering an effective amount of acyclovir or a pharmaceutically acceptable salt.

This claim is broader in route than claim 4. It does not require an injectable carrier or a particular oral dosage form. Tablets, capsules, suspensions, and other oral presentations could potentially fall within the claim if the required compound and therapeutic administration limitations were met.

Claim 17: topical treatment method

Claim 17 covers treating viral infection in a mammal by topically administering an effective amount of acyclovir or a pharmaceutically acceptable salt.

The claim does not identify a cream, ointment, gel, lotion, patch, concentration, or penetration-enhancing system. Those formulation details are therefore not express limitations of claim 17.

How do the dependent claims narrow the patent scope?

Claims 2 and 3 narrow the injectable composition claims by specifying the salt.

Claim	Limitation
1	Injectable acyclovir composition or pharmaceutically acceptable salt
2	Alkali-metal salt
3	Sodium salt of acyclovir
4	Treatment using the injectable composition
5	Human patient
6-10	Specified virus
11	Oral treatment
12-16	Specified virus for oral treatment
17	Topical treatment
18-20	Specified virus for topical treatment

Claim 3 is the narrowest composition claim and specifically covers acyclovir sodium. A formulation using acyclovir rather than its sodium salt could still fall within claim 1, assuming the injectable composition requirements were satisfied, but not necessarily claim 3.

The viral-specific claims do not add formulation limitations. They narrow the patient or disease indication to HSV-1, HSV-2, cytomegalovirus, Epstein-Barr virus, or varicella-zoster virus.

The supplied text uses “vericella Zoster” in claim 20. That spelling does not materially change the apparent intended subject matter, which is varicella-zoster virus.

What formulations are protected by US Patent 4,507,305?

The patent claims provide broad route-based coverage rather than detailed formulation coverage.

Injectable formulations

Claims 1-3 reach injectable acyclovir compositions containing:

Acyclovir or a pharmaceutically acceptable salt;
An effective amount; and
A pharmaceutically acceptable carrier.

The claims do not require acyclovir sodium in every injectable product. Acyclovir sodium is expressly covered by claim 3, while claim 1 also reaches the parent compound and other pharmaceutically acceptable salts.

The absence of a defined excipient list creates potential claim-construction issues. A carrier must be pharmaceutically acceptable, but the claim does not specify whether the carrier must be aqueous, buffered, isotonic, sterile, or preservative-free. Those characteristics may be relevant to regulatory approval and product quality, but they are not stated as express claim limitations.

Oral formulations

Claim 11 covers oral administration but does not expressly require a tablet, capsule, oral solution, or suspension. The central limitations are the active ingredient, effective amount, mammalian viral infection, and oral route.

A generic oral acyclovir product would have been exposed to this claim during the patent term even if its formulation differed materially from the branded product.

Topical formulations

Claim 17 similarly covers topical administration without specifying a particular vehicle. Creams, ointments, gels, and comparable topical dosage forms could potentially satisfy the route limitation if they delivered an effective amount of acyclovir.

Later formulation patents could still have narrowed the commercial freedom to operate during their own terms. Such patents would not extend the term of US Patent 4,507,305.

What viruses are covered by the patent?

The patent identifies the following viruses:

Virus	Injectable method	Oral method	Topical method
HSV-1	Yes	Yes	Yes
HSV-2	Yes	Yes	Yes
Cytomegalovirus	Yes	Yes	No express topical dependent claim
Epstein-Barr virus	Yes	Yes	No express topical dependent claim
Varicella-zoster virus	Yes	Yes	Yes

The parent treatment claims use the broader term “viral infection.” The dependent claims identify specific viruses but do not necessarily exclude other viral infections from the broader independent claims, subject to the ordinary rules governing claim dependency and construction.

The patent’s inclusion of cytomegalovirus and Epstein-Barr virus is broader than the principal current commercial use of acyclovir, which is associated primarily with herpes simplex virus and varicella-zoster virus infections.

When did US Patent 4,507,305 expire?

US Patent 4,507,305 issued on March 26, 1985. As a pre-Uruguay Round Agreements Act patent, its ordinary term was 17 years from issuance. On that basis, the patent expired on March 26, 2002. [1]

Exclusivity timeline

Event	Date or period
Patent issuance	March 26, 1985
Ordinary US patent term	17 years from issuance
Expiration	March 26, 2002
Current enforceability	Expired
Current Paragraph IV significance	None for this patent
Current generic blocking effect	None

The patent predates the modern 20-year term measured from the earliest effective nonprovisional filing date. It therefore falls under the older issuance-based term rules.

No current US market exclusivity can be based on this patent. A patent that has expired cannot support an injunction, damages claim for post-expiration conduct, or a Paragraph IV challenge directed at preventing generic approval.

What is the Orange Book status of US Patent 4,507,305?

US Patent 4,507,305 has no current Orange Book blocking effect because it expired in 2002. The Orange Book lists patents and exclusivity information associated with approved drug products, but an expired patent does not prevent FDA approval of a competing product. [2]

Acyclovir has been marketed in multiple dosage forms, including oral, injectable, and topical products. Orange Book treatment of a particular acyclovir reference product depends on the relevant NDA, dosage form, route, and patent certifications. The existence of an Orange Book listing for another acyclovir-related patent would not revive or extend the term of US Patent 4,507,305.

The principal regulatory pathways for competing products include:

ANDA approval for therapeutically equivalent generic products;
505(b)(2) approval where the applicant relies partly on published data or an approved product but introduces differences requiring additional support; and
Separate applications for materially different dosage forms or delivery systems.

Were Paragraph IV challenges relevant to this patent?

Paragraph IV challenges were potentially relevant during the patent’s term, particularly for generic acyclovir products seeking approval before March 26, 2002. Under the Hatch-Waxman framework, an ANDA applicant could certify that a listed patent was invalid, unenforceable, or would not be infringed. [3]

Today, a Paragraph IV certification against US Patent 4,507,305 would have no practical patent-blocking value because the patent has expired. A generic applicant would not need to wait for the patent’s expiration, and the patent could not support a statutory 30-month stay against FDA approval.

Historical acyclovir patent litigation included disputes involving Burroughs Wellcome’s earlier acyclovir patent estate. In Burroughs Wellcome Co. v. Barr Laboratories, Inc., the Federal Circuit addressed validity and infringement issues involving an earlier acyclovir patent, US Patent 4,199,574, rather than treating US Patent 4,507,305 as a current barrier to generic entry. [4]

Which companies challenged or competed with the acyclovir patent estate?

Acyclovir competition developed through generic manufacturers and through later products based on related technology.

Original innovator and successor

Burroughs Wellcome was the original commercial developer associated with Zovirax and the early US acyclovir patent estate. Glaxo Wellcome later acquired Burroughs Wellcome, and GlaxoSmithKline became the subsequent corporate owner of the Zovirax business.

Generic manufacturers

Acyclovir has been supplied by multiple generic manufacturers in the United States. Generic competition has included oral tablets, capsules, suspensions, injectable products, and topical products, subject to product-specific FDA approvals.

Because US Patent 4,507,305 expired in 2002, current competition does not depend on overcoming this patent. Manufacturers compete on:

FDA-approved dosage forms;
Active pharmaceutical ingredient supply;
Sterile injectable manufacturing;
Product availability;
Contract manufacturing economics;
Hospital and retail contracting; and
Distribution scale.

How does acyclovir compare with valacyclovir?

Valacyclovir is the L-valyl ester prodrug of acyclovir. It was developed to improve oral bioavailability and dosing convenience.

Attribute	Acyclovir	Valacyclovir
Active drug	Acyclovir	Converted to acyclovir in vivo
Oral bioavailability	Lower	Higher
Typical oral dosing convenience	Less favorable	More favorable
Patent landscape	Early patents expired	Later prodrug and formulation patents also largely expired
Biosimilar relevance	None	None
Main competition	Generic acyclovir	Generic valacyclovir

Valacyclovir does not fall within the literal chemical requirement of claims directed to administering acyclovir unless the claim is interpreted to cover administration of a prodrug that delivers acyclovir. The supplied claims do not expressly recite valacyclovir. A valacyclovir product would therefore require separate infringement analysis based on claim construction, prosecution history, and the specific conduct alleged.

Does the patent cover manufacturing methods or API production?

No. The supplied claims do not claim:

A method of synthesizing acyclovir;
A particular intermediate;
A purification process;
A polymorph;
A crystal form;
A particle-size distribution;
A sterile filling process;
A container closure system; or
A manufacturing facility.

The patent could have created product-use exposure for a manufacturer selling a covered product during its term, but it did not independently block every method of producing acyclovir.

Current manufacturing barriers are primarily technical and regulatory. Injectable acyclovir requires validated sterile manufacturing, control of impurities, stability data, container compatibility, and compliance with current good manufacturing practices. Those barriers may be commercially material even though they are not patent barriers created by US Patent 4,507,305.

How strong was the patent estate?

The estate was commercially significant during the 1980s and 1990s because the claims reached multiple administration routes and several clinically important herpes-family viruses. Its breadth came from route and therapeutic-use language rather than from narrow dosage or formulation definitions.

Strengths during the patent term

Coverage of injectable acyclovir compositions;
Specific coverage of acyclovir sodium;
Oral treatment claims;
Topical treatment claims;
Coverage of both human and broader mammalian treatment;
Virus-specific dependent claims;
No stated concentration or dosage restriction.

Potential limitations

Functional “effective amount” language;
Broad carrier requirement without detailed formulation definitions;
Possible prior-art overlap with earlier acyclovir compound patents;
Separate analysis required for prodrugs such as valacyclovir;
No manufacturing-process protection;
No current enforceability after expiration.

The patent’s present legal strength is zero as an enforceable US patent right because it expired in 2002. Its remaining value is historical, analytical, and relevant to understanding the development of acyclovir products and earlier generic entry strategies.

What licensing deals affected acyclovir commercialization?

The principal commercial history reflects Burroughs Wellcome’s development and subsequent corporate succession into Glaxo Wellcome and GlaxoSmithKline. The supplied patent claims do not identify a licensee or field-of-use restriction.

No current license is required to practice the expired patent. A company may still require licenses for separate live patents, trademarks, know-how, regulatory data, manufacturing technology, or commercial agreements, but those rights are distinct from US Patent 4,507,305.

What generic launch risks exist today?

US Patent 4,507,305 does not create a generic launch risk today. The relevant risks are operational and regulatory:

Demonstrating pharmaceutical equivalence and bioequivalence for the applicable dosage form.
Meeting sterile manufacturing standards for injectable acyclovir.
Controlling impurities and degradation products.
Establishing adequate stability and container-closure performance.
Assessing later patents covering specific formulations, delivery systems, or manufacturing processes.
Maintaining reliable API supply and FDA-compliant manufacturing operations.
Avoiding trademark and labeling issues associated with branded Zovirax products.

For standard oral acyclovir, the patent barrier is effectively absent. Injectable acyclovir may carry greater development cost because of sterile manufacturing requirements, but that cost is not attributable to US Patent 4,507,305.

Key Takeaways

US Patent 4,507,305 covers acyclovir compositions and methods of injectable, oral, and topical treatment.
Claim 3 specifically covers injectable acyclovir sodium.
Claims 11 and 17 cover oral and topical treatment methods without specifying particular dosage forms.
The patent identifies HSV-1, HSV-2, cytomegalovirus, Epstein-Barr virus, and varicella-zoster virus.
The patent issued on March 26, 1985, and expired on March 26, 2002.
It has no current Orange Book blocking effect and cannot support a current Paragraph IV stay.
It does not claim acyclovir synthesis, polymorphs, sterile filling, or manufacturing processes.
Current acyclovir market barriers are regulatory, manufacturing, supply-chain, and commercial rather than patent-based.
Valacyclovir requires separate analysis because the supplied claims do not expressly recite the prodrug.

FAQs

Is US Patent 4,507,305 still enforceable?

No. The patent expired on March 26, 2002, based on its 17-year term from issuance.

Does US Patent 4,507,305 cover Zovirax cream?

Its topical method claim can reach topical administration of acyclovir, but the patent does not identify a specific cream vehicle, concentration, or branded product. Any later formulation patents require separate analysis.

Does the patent cover valacyclovir?

The supplied claims recite acyclovir or its pharmaceutically acceptable salts, not valacyclovir. Valacyclovir is a prodrug and requires a separate claim-construction and patent analysis.

Is acyclovir subject to biosimilar competition?

No. Acyclovir is a chemically synthesized small molecule, not a biologic. Competition proceeds through generic-drug pathways rather than biosimilar approval.

Can a company launch generic injectable acyclovir without licensing this patent?

Yes, this patent is expired. The company must still satisfy FDA approval, sterile manufacturing, quality, labeling, and any separately applicable live intellectual-property rights.

References

United States Patent and Trademark Office. (1985). US Patent No. 4,507,305, antiviral compositions and methods.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
U.S. Food and Drug Administration. (2015). ANDA submissions: Refuse-to-receive standards.
Burroughs Wellcome Co. v. Barr Laboratories, Inc., 828 F.2d 1557 (Fed. Cir. 1987).

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	244227	⤷ Start Trial
Austria	15899	⤷ Start Trial
Australia	572086	⤷ Start Trial
Australia	8389282	⤷ Start Trial
Brazil	8202931	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,507,305

Summary for Patent: 4,507,305