U.S. Patent 5,595,978: Scope, Claims, Expiration, and CMV Retinitis Patent Landscape

U.S. Patent No. 5,595,978 covers the intravitreal use of an antisense oligonucleotide identified as SEQ ID NO: 1 for treating cytomegalovirus retinitis, related buffered compositions, and combination treatment with ganciclovir or foscarnet. SEQ ID NO: 1 corresponds to fomivirsen, also known as ISIS 2922, the active ingredient in Vitravene.

The patent is an expired U.S. right. Its claims therefore do not currently block manufacture, formulation, or sale in the United States, although separate patents, regulatory requirements, trade secrets, or third-party rights could affect a commercial program.

What drug and sequence does U.S. Patent 5,595,978 cover?

U.S. Patent 5,595,978 is directed to an antisense oligonucleotide for CMV retinitis. SEQ ID NO: 1 is the 21-nucleotide sequence used for fomivirsen:

5'-GCG TTT GCT CTT CTT CTT GCG-3'

Fomivirsen is a phosphorothioate antisense oligodeoxynucleotide designed to bind CMV immediate-early gene transcripts, particularly sequences associated with CMV replication. Vitravene was administered by intravitreal injection for CMV retinitis in immunocompromised patients.

The claims supplied identify the protected subject matter as follows:

Claim	Subject matter	Scope
1	Treatment of CMV retinitis by intravitreal administration of SEQ ID NO: 1	Independent method claim
2	Claim 1 with a buffered solution	Dependent method claim
3	Claim 1 where the animal is human	Dependent method claim
4	Composition containing SEQ ID NO: 1 and a pharmaceutically acceptable carrier	Independent composition claim
5	Composition containing SEQ ID NO: 1 and bicarbonate buffered solution	Dependent composition claim
6	Claim 4 composition administered intravitreally with ganciclovir	Combination method claim
7	Claim 5 composition administered intravitreally with ganciclovir	Narrower combination method claim
8	Claim 4 composition administered intravitreally with foscarnet	Combination method claim
9	Claim 5 composition administered intravitreally with foscarnet	Narrower combination method claim

What does claim 1 of U.S. Patent 5,595,978 require?

Claim 1 requires all of the following elements:

A method for treating CMV retinitis.
An animal having CMV retinitis.
Intravitreal injection.
An effective amount.
A composition containing SEQ ID NO: 1.
A pharmaceutically acceptable carrier.

The claim is narrower than a general CMV treatment claim. It does not cover every administration route, every CMV disease, or every antisense sequence. A potentially infringing use would need to involve treatment of CMV retinitis through intravitreal injection using a composition containing the claimed sequence.

The claim does not expressly require:

A particular dose.
A particular injection volume.
A particular dosing frequency.
A specified phosphorothioate pattern.
A specific salt or counterion.
Concomitant use of ganciclovir or foscarnet.
Human treatment, because “animal” is broader and claim 3 separately specifies a human.

The word “comprising” generally makes the claim open-ended. A composition containing SEQ ID NO: 1 and additional active ingredients or excipients could fall within the claim, provided the other limitations are met.

How broad is the composition claim?

Claim 4 is the broadest composition claim in the supplied set. It covers a composition comprising SEQ ID NO: 1 and a pharmaceutically acceptable carrier.

The claim does not limit the carrier to bicarbonate buffer. Claim 5 is narrower because it requires a bicarbonate buffered solution. Claim 4 can potentially encompass:

Aqueous buffered formulations.
Non-bicarbonate buffers.
Isotonic formulations.
Formulations containing additional excipients.
Formulations containing another antiviral agent.
Different concentrations of the oligonucleotide.

The scope depends on how “SEQ ID NO: 1” is construed in the patent specification. For an oligonucleotide claim, relevant issues include whether the sequence designation incorporates:

A specific phosphorothioate backbone.
A particular 5' or 3' chemistry.
Modified nucleobases.
A defined molecular weight range.
A specific stereochemical configuration.
A particular salt or formulation form.

The supplied claims alone do not resolve those construction questions. The sequence is the central limitation, but the patent specification and prosecution history determine whether the sequence designation covers only the disclosed chemical form of fomivirsen or broader chemical variants retaining the same base sequence.

What formulations are protected by claims 2, 5, and 7?

Claim 2 covers the claim 1 treatment method when the pharmaceutically acceptable carrier is a buffered solution.

Claim 5 covers a composition containing SEQ ID NO: 1 and a bicarbonate buffered solution. It is narrower than claim 4 because bicarbonate is mandatory.

Claims 7 and 9 incorporate the bicarbonate formulation limitation into combination treatment with ganciclovir or foscarnet.

Formulation limitation	Claim coverage
Any pharmaceutically acceptable carrier	Claims 1 and 4
Buffered solution	Claims 2 and, through dependency, 5-related methods
Bicarbonate buffered solution	Claim 5 and claims 7 and 9
Non-bicarbonate buffer	Potentially claim 2, but not claim 5
Carrier with additional excipients	Potentially claims 1 and 4 if all limitations are satisfied
Carrier without SEQ ID NO: 1	Outside the supplied claims

A formulation containing a different antisense sequence would not meet the literal SEQ ID NO: 1 limitation. A formulation containing the same base sequence but a materially different chemical backbone could present a claim-construction issue.

What do the ganciclovir and foscarnet combination claims cover?

Claims 6 through 9 cover combination treatment. They require intravitreal administration of the claimed fomivirsen composition together with either ganciclovir or foscarnet.

The claims do not state whether the two agents must be:

Injected in the same syringe.
Administered during the same procedure.
Administered on the same day.
Administered sequentially.
Used at a specific dose or schedule.

The ordinary infringement analysis would focus on whether the accused treatment uses the claimed composition intravitreally and includes ganciclovir or foscarnet as part of the treatment regimen. The claims do not appear to require that ganciclovir or foscarnet also be administered intravitreally. That issue would depend on the claim language, specification, and prosecution history.

The combination claims were clinically relevant because ganciclovir and foscarnet were established anti-CMV agents. They also created narrower fallback positions if the standalone treatment or composition claims were challenged.

When did U.S. Patent 5,595,978 lose exclusivity?

U.S. Patent 5,595,978 issued on January 21, 1997. It is expired and no longer provides enforceable patent exclusivity in the United States.

For a pre-Uruguay Round Agreements Act patent application, the applicable term was generally 17 years from issuance, subject to the statutory rules in effect for the application and any patent-term adjustment or extension. On that basis, the patent term ended in January 2014. The patent is therefore not a current barrier to a U.S. generic, reformulated product, or new fomivirsen development program.

Event	Date
Patent issued	January 21, 1997
Approximate 17-year term endpoint	January 21, 2014
Current status	Expired
Current enforceable patent exclusivity from this patent	None

The expiration of this patent does not eliminate other possible rights. A commercialization review should distinguish between:

Expired composition and method claims.
Later continuation or divisional patents.
Formulation patents.
Manufacturing patents.
Regulatory exclusivity.
Product-specific trademarks.
Confidential manufacturing know-how.

What was the FDA regulatory status of fomivirsen?

The FDA approved Vitravene, containing fomivirsen sodium, for intravitreal treatment of CMV retinitis in immunocompromised patients. The product was approved under NDA 20-961 in 1998. Fomivirsen was one of the first antisense drugs to receive FDA approval.

Its regulatory profile differs from that of a conventional small-molecule antiviral:

Regulatory issue	Fomivirsen status
Active ingredient	Fomivirsen sodium
Product	Vitravene
Route	Intravitreal injection
Indication	CMV retinitis
FDA approval	1998
Regulatory pathway	New drug application
Chemical class	Antisense phosphorothioate oligonucleotide
Biosimilar pathway	Generally not applicable
Historical orphan-drug exclusivity	Seven years from approval, subject to statutory scope
Commercial status	Vitravene was later withdrawn from commercial availability

Orphan-drug exclusivity would have expired well before the patent term ended. FDA orphan exclusivity does not extend patent rights, and patent expiration does not automatically create FDA approval for a competing product.

What is the Orange Book status of fomivirsen?

Vitravene was an FDA-approved drug product and its patent information could be evaluated under the Orange Book framework applicable to the NDA. The Orange Book does not create patent rights. It records patents submitted by an NDA holder and supports the Hatch-Waxman certification process.

Because U.S. Patent 5,595,978 has expired, a historical Orange Book listing for that patent would no longer create a current patent-based barrier to approval. A current applicant would still need to address any live patents listed for the relevant reference product, if any remain, and comply with the applicable FDA requirements for the proposed product.

A key practical point is that fomivirsen is not an ordinary small-molecule tablet or injectable generic. An applicant would need to establish pharmaceutical equivalence or the applicable alternative standard for a complex oligonucleotide product, including controls for:

Sequence identity.
Chain-length distribution.
Backbone chemistry.
Purity and related oligonucleotide impurities.
Aggregation.
Sterility and endotoxin.
Potency and antiviral activity.
Formulation and container closure.
Intravitreal tolerability.

Are biosimilar risks relevant to fomivirsen?

Biosimilar risk is limited because fomivirsen is a chemically synthesized oligonucleotide rather than a therapeutic protein. The Biologics Price Competition and Innovation Act biosimilar pathway under section 351(k) is generally directed to biological products. A fomivirsen competitor would more likely require an NDA or another FDA pathway applicable to the product's regulatory classification.

That does not make development easy. The principal barriers are technical and regulatory rather than patent-based:

Demonstrating sameness or sufficient comparability of the oligonucleotide.
Establishing control of chemical impurities.
Demonstrating sterility for intraocular administration.
Supporting local ocular safety.
Addressing the discontinued reference product.
Establishing a commercially viable indication in a substantially changed CMV treatment market.

Which companies challenged or competed with the Vitravene patent estate?

The principal commercial parties associated with the product were Isis Pharmaceuticals, now Ionis Pharmaceuticals, and Ciba Vision, which commercialized Vitravene. The historic market also included Roche's ganciclovir products and AstraZeneca's foscarnet product, depending on the period and jurisdiction.

There is no current meaningful Paragraph IV challenge landscape for U.S. Patent 5,595,978 because the patent has expired. Any historical ANDA certification activity would no longer create a live litigation risk under this patent.

The modern competitive landscape is also materially different from the 1990s:

Systemic and local anti-CMV therapies have changed.
The population with AIDS-related CMV retinitis has declined because of effective antiretroviral therapy.
Ganciclovir and foscarnet remain clinically relevant historical comparators.
Other CMV drugs, including letermovir, target different clinical settings and are not direct substitutes for intravitreal fomivirsen in all use cases.
A new fomivirsen program would compete against current clinical practice, not only against the historical Vitravene product.

How strong was the patent estate?

The supplied claims created a focused but commercially meaningful estate around the specific sequence, route, indication, and selected combinations.

Strength factor	Assessment
Sequence specificity	Strong against products using the identical claimed sequence
Route limitation	Narrows enforcement to intravitreal administration
Disease limitation	Narrows enforcement to CMV retinitis
Composition claim	Broadest claim category in the supplied set
Buffer claim	Narrower, formulation-specific protection
Combination claims	Provides fallback protection for regimens using ganciclovir or foscarnet
Manufacturing coverage	Not shown in the supplied claims
Broad CMV antiviral coverage	Not shown; claims are sequence and use specific
Current enforceability	None because the patent expired

The composition claim was the most commercially important claim because it could reach the formulated drug product independently of a particular treatment act. The treatment claims were narrower but directly aligned with the approved product's use.

The estate's present strength is therefore historical rather than exclusionary. It can affect freedom-to-operate analyses, patent validity research, and prior-art assessments, but it does not presently prevent U.S. commercialization.

What generic launch risks exist after patent expiration?

A generic or follow-on launch would face low patent risk from U.S. Patent 5,595,978 itself. The principal risks would be regulatory, technical, clinical, and commercial.

Risk category	Current assessment
Patent infringement under 5,595,978	Low; patent expired
Paragraph IV litigation under 5,595,978	No current blocking risk
Biosimilar substitution	Generally not the expected pathway
Sequence and impurity control	High technical importance
Sterile intraocular manufacturing	High
Clinical demand	Limited and indication-specific
Reference-product availability	Complicates regulatory strategy
Manufacturing know-how	Potentially significant if not publicly disclosed
Freedom to operate outside the United States	Must be assessed jurisdiction by jurisdiction
Commercial return	Likely constrained by the small and changed CMV retinitis market

What geographic patent coverage remains?

The expiration analysis applies to the U.S. patent identified in the question. Patent rights are territorial. Foreign counterparts may have had different:

Filing dates.
Patent terms.
Patent-term extensions.
Supplementary protection certificates.
Continuation or divisional claims.
Opposition outcomes.
Maintenance-fee histories.

A U.S. freedom-to-operate conclusion cannot be extended automatically to Europe, Japan, Canada, Australia, or other markets. Any foreign launch would require a separate family-level review of issued claims and national legal status.

Key Takeaways

U.S. Patent 5,595,978 covers fomivirsen, identified as SEQ ID NO: 1, for intravitreal treatment of CMV retinitis.
Claim 4 is the broadest supplied claim because it covers a composition containing the sequence and a pharmaceutically acceptable carrier.
Claims 5, 7, and 9 narrow protection to bicarbonate-buffered formulations.
Claims 6 and 7 cover combination use with ganciclovir.
Claims 8 and 9 cover combination use with foscarnet.
The patent issued January 21, 1997 and expired in January 2014 under the applicable historical U.S. patent-term framework.
There is no current enforceable exclusivity from this patent and no live Paragraph IV barrier based on it.
Fomivirsen is a chemically synthesized antisense oligonucleotide, so biosimilar analysis is generally less relevant than NDA, comparability, sterility, and product-quality analysis.
The main present barriers to a follow-on product are regulatory and manufacturing complexity, not this expired patent.
Foreign patent status must be reviewed separately.

FAQs About U.S. Patent 5,595,978 and Fomivirsen

Does U.S. Patent 5,595,978 cover all antisense treatments for CMV?

No. The supplied claims are limited to a composition containing SEQ ID NO: 1 and, for the method claims, intravitreal treatment of CMV retinitis. A different antisense sequence would generally fall outside the literal claims.

Does the patent cover systemic administration of fomivirsen?

The supplied method claims require intravitreal injection or intravitreal administration. Systemic, oral, intravenous, or other routes are outside those method claims unless separately covered by another claim or patent.

Does a fomivirsen product need to use bicarbonate buffer?

No. Claim 4 covers a composition with a pharmaceutically acceptable carrier without requiring bicarbonate. Bicarbonate is required only for the narrower claim 5 and claims dependent on it.

Could a company launch a fomivirsen product without a Paragraph IV challenge?

The expired status of U.S. Patent 5,595,978 means that a Paragraph IV certification to this patent would not be needed as a strategy to defeat a live patent barrier. FDA approval, product classification, and any other unexpired patents would remain separate issues.

Is a new intravitreal CMV oligonucleotide automatically free of patent risk?

No. A different sequence may avoid the supplied claims, but risk could arise from later patents covering modified oligonucleotides, delivery systems, formulations, manufacturing processes, dosing regimens, or other antiviral combinations.

References

U.S. Patent No. 5,595,978. (1997). United States Patent and Trademark Office.
U.S. Food and Drug Administration. (1998). Vitravene prescribing information and approval materials for fomivirsen sodium, NDA 20-961.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Orange Book.
U.S. Food and Drug Administration. (2024). Orphan drug designation and exclusivity provisions.
Ionis Pharmaceuticals, Inc. (n.d.). Fomivirsen and antisense oligonucleotide development history.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
	PCT/US91/05815	Aug 14, 1991

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	154947	⤷ Start Trial
Austria	159025	⤷ Start Trial
Austria	160353	⤷ Start Trial
Austria	168561	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,595,978

Summary for Patent: 5,595,978