United States Patent 5,208,256: Claim Scope, Expiration, Orange Book Relevance, and Patent Landscape for Unoprostone-Polysorbate Ophthalmic Therapy

U.S. Patent No. 5,208,256 protects ocular administration of a synergistic combination of a 13,14-dihydro-15-keto-20-loweralkyl prostaglandin and a polyoxyethylenesorbitan unsaturated higher aliphatic acid monoester. The narrowest commercially relevant embodiment is unoprostone isopropyl, also known as isopropyl unoprostone or unoprostone isopropyl ester, combined with polysorbate 80. The patent covers both treatment methods and pharmaceutical compositions.

The patent issued May 4, 1993. Based on the pre-Uruguay Round patent term applicable to an early-issued U.S. patent, its ordinary term ended May 4, 2010, absent a term adjustment or later enforceable continuation. The patent therefore does not currently present an enforceable U.S. exclusion right. Its historical relevance is strongest for Rescula, the former unoprostone isopropyl ophthalmic product.

What invention does U.S. Patent 5,208,256 protect?

The patent claims an ocular hypotensive combination in which the prostaglandin active ingredient is administered with a polysorbate-type surfactant. The claimed combination is characterized as "oculo-hypotensively synergistic," meaning the combined components are asserted to reduce intraocular pressure more effectively than would be expected from their separate effects.

The central claim architecture is:

Claim element	Scope
Disease or condition	Ocular hypertension; claim 9 expressly includes glaucoma
Route	Ocular administration
Active component	13,14-dihydro-15-keto-20-loweralkyl prostaglandin, salt, or ester
Surfactant component	Polyoxyethylenesorbitan unsaturated higher aliphatic acid monoester
Functional limitation	Combination must be oculo-hypotensively synergistic
Ratio	Claim 7 specifies component (a):(b) of 1:1 to 1:500
Administration timing	Simultaneous or sequential administration
Dosage form	Pharmaceutical composition with carrier, diluent, or excipient

The patent is not limited to a single molecule in claim 1. It begins with a genus covering selected prostaglandin structures and then narrows through dependent claims to 20-ethyl prostaglandins, the F2α series, and the corresponding ester or salt forms.

What are the independent claims in Patent 5,208,256?

Claims 1 and 10 are the principal independent claims.

Claim 1: method-of-treatment claim

Claim 1 requires all of the following:

A subject in need of treatment.
Ocular hypertension as the therapeutic target.
Ocular administration.
A 13,14-dihydro-15-keto-20-loweralkyl prostaglandin, salt, or ester.
A polyoxyethylenesorbitan unsaturated higher aliphatic acid monoester.
A combination that is oculo-hypotensively synergistic.

The claim is a treatment method, not a claim to the prostaglandin molecule standing alone. It does not cover every use of unoprostone, every ophthalmic formulation containing unoprostone, or every use of polysorbate 80.

Claim 10: pharmaceutical composition claim

Claim 10 covers a pharmaceutical composition for ocular administration containing the same two-component combination in association with a pharmaceutically acceptable carrier, diluent, or excipient.

This claim reaches the formulated product rather than the act of administering it. A product must contain both the specified prostaglandin component and the specified polysorbate class. A formulation containing unoprostone without the claimed surfactant would not literally satisfy claim 10.

How do claims 2 through 9 narrow the patent scope?

The dependent claims create a progression from a chemical genus to the commercially important unoprostone embodiment.

Claim	Limitation
2	13,14-dihydro-15-keto-20-loweralkyl prostaglandin A, B, C, D, E, or F
3	20-ethyl member of the A-F prostaglandin series
4	20-loweralkyl prostaglandin F2α
5	20-ethyl prostaglandin F2α
6	Polyoxyethylenesorbitan monooleate
7	Component ratio of 1:1 to 1:500
8	Simultaneous or sequential administration
9	Treatment of glaucoma
11	20-ethyl prostaglandin F2α, preferably its lower alkyl ester, with polyoxyethylenesorbitan monooleate

Claim 11 is the commercially most important composition claim. It combines:

13,14-dihydro-15-keto-20-ethyl prostaglandin F2α;
a salt or lower alkyl ester; and
polyoxyethylenesorbitan monooleate.

Unoprostone isopropyl is the relevant lower alkyl ester associated with the Rescula product. Polysorbate 80 is commonly identified chemically as polyoxyethylene sorbitan monooleate. The correspondence between the chemical claim language and product excipient identity is therefore central to any historical infringement analysis.

Does the patent cover unoprostone isopropyl and polysorbate 80?

Yes, the claim structure is directed to that combination.

Unoprostone isopropyl is the isopropyl ester of 13,14-dihydro-15-keto-20-ethyl prostaglandin F2α. It falls within claim 5 and the active-agent limitation in claim 11. Polysorbate 80 is a polyoxyethylenesorbitan monooleate and falls within claim 6 and the surfactant limitation in claim 11.

The most direct product-level coverage is therefore claim 11. The broader claims may also apply depending on the exact identity, salt or ester form, excipient composition, ratio, and intended use.

What does the "synergistic" limitation require?

The term "synergistic" is a substantive claim limitation. It is not merely a description of the invention.

For a claim 1 or claim 10 infringement theory, the combination would ordinarily need to satisfy the patent's technical standard for oculo-hypotensive synergy. The specification and prosecution history would be important in determining whether synergy requires:

a statistically demonstrated interaction;
greater-than-additive intraocular-pressure reduction;
a specified dose-response relationship;
improved efficacy at reduced prostaglandin dosage; or
the results shown in the patent's examples.

The supplied claims alone do not define the precise evidentiary threshold. A court would construe the term in view of the specification, expert testimony, and prosecution history. A formulation containing both ingredients would not automatically establish infringement if the combination did not meet the interpreted synergy requirement.

The limitation creates both value and vulnerability. It supports a technical distinction over simple co-formulation, but it also creates a potential noninfringement issue for products using the same ingredients without the claimed pharmacodynamic relationship.

What formulations are protected by Patent 5,208,256?

The patent protects formulations that combine the claimed prostaglandin with a qualifying polyoxyethylenesorbitan monoester.

Directly relevant surfactant

The most important surfactant is polysorbate 80, also called polyoxyethylene sorbitan monooleate. Claim 6 narrows the surfactant to monooleate, and claim 11 incorporates that limitation with the 20-ethyl prostaglandin F2α embodiment.

Other polyoxyethylenesorbitan monoesters may fall within the broader claim 1 language if their fatty-acid component is an unsaturated higher aliphatic acid. The exact scope depends on the chemical identity and claim construction.

Formulation characteristics

Claim 10 does not specify:

a particular concentration of unoprostone;
a particular concentration of surfactant;
a particular pH;
a preservative;
a buffer;
a viscosity modifier;
a specific bottle or delivery device; or
a particular commercial brand.

Those formulation features may be present in the specification or regulatory product, but they are not express limitations in the quoted claim 10.

Ratio limitation

Claim 7 requires a component (a):(b) ratio from 1:1 to 1:500. The patent specification and prosecution history would determine whether the ratio is measured by weight, molar amount, concentration, or another basis. In commercial formulation analysis, the relevant calculation must use the measurement convention supported by the patent record.

A product outside the claim 7 ratio may still fall within claim 1 or claim 10 because claim 7 is dependent and does not limit the broader independent claims.

When did U.S. Patent 5,208,256 lose exclusivity?

The patent issued on May 4, 1993, and its ordinary pre-1995 patent term was 17 years from issuance. On that basis, the term ended May 4, 2010. Patent term adjustment generally does not apply to a patent issued under the older term regime in a manner that would extend the patent beyond the applicable statutory term without a specific basis.

Event	Date or status
U.S. patent issued	May 4, 1993
Ordinary term basis	17 years from issue
Expected ordinary expiration	May 4, 2010
Current enforceability	Expired by ordinary term
Current U.S. blocking effect	None from this patent alone

The expiration date should be confirmed against the official USPTO patent record and any terminal disclaimer or unusual term calculation. The claim analysis remains relevant for historical infringement, licensing, invalidity, and freedom-to-operate assessments covering the period before expiration.

What was the FDA and Orange Book status of the covered product?

The principal commercial product associated with this patent was Rescula, an ophthalmic solution containing unoprostone isopropyl. Rescula was approved by the FDA under NDA 020599 for reduction of elevated intraocular pressure in patients with open-angle glaucoma or ocular hypertension. The product was later discontinued from commercial distribution. FDA drug discontinuation does not by itself establish withdrawal for safety or effectiveness reasons. [2]

The Orange Book historically provided the relevant patent-listing framework for approved small-molecule products. Rescula, as an NDA product, was subject to Hatch-Waxman patent certification rules for any ANDA applicant seeking approval of a generic equivalent. [3][4]

Because Patent 5,208,256 expired in 2010, it no longer creates a current Paragraph IV barrier. Any later applicant would not need to wait for this patent's expiration, although other listed patents, regulatory exclusivities, formulation differences, or product-specific requirements could have affected approval timing.

Were Paragraph IV challenges or patent litigation associated with this patent?

A Paragraph IV certification would have been the statutory mechanism for challenging an unexpired listed patent in an ANDA. For Patent 5,208,256, that mechanism became commercially relevant only before its 2010 expiration.

The supplied claim record does not identify a particular ANDA filer, notice letter, district court action, settlement, or consent judgment. No litigation conclusion should be drawn solely from the patent claims. A complete litigation history would require matching the patent against:

FDA Orange Book patent listings;
ANDA litigation complaints under 21 U.S.C. § 355(j);
USPTO assignment and maintenance records;
PACER district court filings; and
settlement or license agreements involving the patent owner.

The patent's expiration materially reduces the significance of any historical litigation. An unexpired continuation or division would need separate analysis because expiration of one patent does not terminate a distinct later-issued patent.

How strong is the patent estate?

The patent's historical strength was concentrated in a specific product architecture rather than in the unoprostone molecule generally.

Estate characteristic	Assessment
Chemical composition coverage	Limited; the claims are directed to defined prostaglandin derivatives in combination with a surfactant
Method-of-use coverage	Meaningful for ocular hypertension and glaucoma
Formulation coverage	Meaningful where unoprostone or a qualifying analog is combined with polysorbate-type monoester
Device coverage	None apparent from the quoted claims
Manufacturing coverage	None apparent from the quoted claims
Broad molecule monopoly	No; the claims do not cover unoprostone in all uses or formulations
Current exclusionary strength	None, because the patent term has expired
Historical product relevance	High for the unoprostone-polysorbate ophthalmic formulation

The patent was narrower than a composition-of-matter patent covering unoprostone itself. It also did not claim a manufacturing process, crystalline form, container, preservative system, or delivery device. Its commercial leverage depended on the product using the claimed combination and on the enforceability of the synergy limitation.

How does this patent compare with competing glaucoma drug patent estates?

Unoprostone differs from major prostaglandin analog products such as latanoprost, bimatoprost, and travoprost because Patent 5,208,256 is centered on a combination of active ingredient and surfactant, rather than a broad standalone molecule claim.

Product or class	Main historical patent strategy	Relationship to Patent 5,208,256
Unoprostone isopropyl	Combination and formulation claims involving polysorbate-type surfactant	Directly relevant
Latanoprost	Compound, formulation, and method claims developed around latanoprost products	Generally outside the chemical genus claimed here
Bimatoprost	Compound, formulation, and therapeutic-use claims	Generally outside the claimed prostaglandin structure
Travoprost	Compound and formulation claims	Generally outside the claimed unoprostone structure
Timolol products	Beta-blocker composition and use claims	Outside the claimed prostaglandin combination

This patent does not create biosimilar risk. Unoprostone is a small molecule regulated through the ANDA pathway, not a biologic regulated under the biosimilar pathway. The relevant competitive risks are generic substitution, alternative glaucoma therapies, manufacturing capability, and regulatory approval of an equivalent ophthalmic formulation.

What generic launch risks existed and what risks remain?

Before May 4, 2010, a generic unoprostone product using the claimed combination could have faced:

an Orange Book-listed patent challenge;
a Paragraph IV notice-letter dispute;
a 30-month stay under Hatch-Waxman if litigation was timely filed;
formulation-equivalence issues;
proof problems concerning the synergy limitation; and
potential exclusivity or approval-status issues under the NDA.

After expiration, Patent 5,208,256 no longer supports an injunction against a qualifying generic product. Remaining commercial barriers would be regulatory rather than patent-based, including:

availability of reference-product information;
pharmaceutical equivalence and bioequivalence requirements;
preservative and excipient compatibility;
sterile ophthalmic manufacturing;
container-closure performance;
supply of unoprostone active pharmaceutical ingredient; and
market demand for a discontinued product.

A generic manufacturer could also design around the claim by omitting polysorbate 80, using a different excipient system, or selecting a formulation outside a dependent ratio limitation. Such designs would still require separate analysis against any later patents.

What licensing and geographic rights should be evaluated?

The patent is a U.S. right. It does not establish protection in Japan, Europe, Canada, or other jurisdictions. Foreign counterpart patents would require separate family-level review, including national filing dates, prosecution outcomes, patent-term adjustments, supplementary protection certificates, and abandonment status.

The commercial product history indicates that licensing, development, or commercialization rights may have involved the originator and regional ophthalmology companies. Patent ownership, however, cannot be inferred from product marketing alone. Assignment records and executed license agreements are required to establish:

original owner;
assignment chain;
exclusive versus nonexclusive rights;
field-of-use restrictions;
territorial rights;
sublicensing rights; and
royalty obligations.

The quoted claims reveal no manufacturing or process barrier. Any supply-chain restriction would arise from separate process patents, trade secrets, regulatory know-how, or limited API manufacturing capacity rather than from Patent 5,208,256 itself.

Key Takeaways

U.S. Patent 5,208,256 covers ocular treatment and pharmaceutical compositions using a defined 13,14-dihydro-15-keto-20-loweralkyl prostaglandin with a polyoxyethylenesorbitan unsaturated fatty-acid monoester.
The commercially important embodiment is unoprostone isopropyl combined with polysorbate 80.
Claim 1 is a broad method claim; claim 10 is the corresponding composition claim.
Claim 11 is the most specific product-oriented claim for the unoprostone-polysorbate combination.
The patent also includes ocular hypertension, glaucoma, simultaneous or sequential administration, and a 1:1 to 1:500 ratio limitation.
The patent issued May 4, 1993, and its ordinary term ended May 4, 2010.
The patent does not currently block generic or other commercial activity in the United States.
It does not cover unoprostone in every formulation, every use, or every jurisdiction.
It is not a biosimilar patent issue. Unoprostone is a small molecule subject to the ANDA framework.
Any current freedom-to-operate analysis must review later patents, foreign counterparts, FDA records, assignments, and litigation independently.

FAQs About U.S. Patent 5,208,256

Does Patent 5,208,256 cover unoprostone by itself?

No. The quoted claims require unoprostone or a qualifying related prostaglandin to be used with a polyoxyethylenesorbitan unsaturated higher aliphatic acid monoester.

Is polysorbate 80 the same as polyoxyethylenesorbitan monooleate?

Yes. Polysorbate 80 is commonly identified as polyoxyethylene sorbitan monooleate. Its exact specification and grade may matter in a historical claim analysis.

Could a formulation using unoprostone without polysorbate 80 infringe?

Not literally under the quoted combination claims because the surfactant limitation would be absent. Separate patents or a doctrine-of-equivalents analysis could produce a different result.

Did the patent protect Rescula's delivery bottle or preservative system?

Not from the quoted claims. The claims identify the active combination, surfactant, therapeutic use, administration timing, ratio, and conventional pharmaceutical excipients, but do not expressly claim a bottle or specific preservative.

Is a continuation patent automatically covered by the May 4, 2010 expiration date?

No. A continuation or divisional would have to be identified and analyzed separately. Its term and enforceability could differ from the parent patent, subject to the applicable patent-term rules.

References

U.S. Patent No. 5,208,256. (1993). Ophthalmic composition and method for treatment of ocular hypertension. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: Rescula (unoprostone isopropyl ophthalmic solution), NDA 020599. https://www.accessdata.fda.gov/scripts/cder/daf/
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book-data-files
Drug Price Competition and Patent Term Restoration Act of 1984, 21 U.S.C. § 355(j).
Leahy-Smith America Invents Act, 35 U.S.C. §§ 154, 156.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	2-132909	May 22, 1990

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	114470	⤷ Start Trial
Canada	2042972	⤷ Start Trial
Germany	69105349	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,208,256

Summary for Patent: 5,208,256