U.S. Patent 5,438,071: Porfimer Sodium Claims, Scope, Expiration and Patent Landscape

U.S. Patent 5,438,071 protects a defined porfimer sodium composition in which fewer than 10% of covalent linkages between porphyrin units are ester linkages. The patent also covers specified porphyrin oligomer mixtures and alkaline processing conditions used to produce the low-ester material. Its U.S. term expired in February 2012, eliminating current U.S. blocking rights, although the claims remain relevant to historical patent scope, freedom-to-operate analysis, and the provenance of Photofrin-related intellectual property. (U.S. Patent No. 5,438,071, 1995; USPTO, n.d.)

What does U.S. Patent 5,438,071 protect?

The patent protects three related subject matter categories:

A porfimer sodium pharmaceutical composition with fewer than 10% ester linkages.
A biologically active porphyrin oligomer mixture containing two to eight porphyrin units.
A composition made by treating acetylated hematoporphyrin with sodium hydroxide under specified conditions.

The central technical distinction is the ratio of ether to ester linkages. The patent does not broadly claim every porfimer preparation or every photodynamic porphyrin composition. It claims a porfimer material meeting a quantitative chemical limitation and, in several claims, a specified manufacturing history.

Patent identification

Item	Details
U.S. patent	5,438,071
Subject matter	Porphyrin oligomers with reduced ester linkages
Patent type	Utility patent
Grant date	August 1, 1995
Priority basis	February 1992 U.S. priority record
Product association	Porfimer sodium, commercially associated with Photofrin
Core limitation	Less than 10% ester linkages among porphyrin oligomer linkages
Claims	Composition, biologically active composition, and process-defined composition
U.S. expiration	February 2012, based on the applicable 20-year term
Current enforceability	Expired
Regulatory relevance	Photofrin and porfimer sodium

The patent’s commercial importance arose from the relationship between molecular composition and photodynamic performance. Porfimer sodium is a heterogeneous mixture of porphyrin oligomers rather than a single molecular entity. The patent attempted to define a commercially useful material by its linkage distribution, oligomer size, biological activity, and manufacturing process.

How broad are the claims of U.S. Patent 5,438,071?

The claims are narrower than a general claim to porfimer sodium or photodynamic therapy.

Claim 1: composition defined by linkage ratio

Claim 1 requires:

Porfimer sodium;
Porphyrin oligomers;
Ether and ester covalent linkages;
Fewer than 10% ester linkages; and
A pharmaceutically acceptable carrier.

The claim is a composition claim. Infringement would require the accused product to satisfy the low-ester limitation. A porphyrin product with an unknown, equal to, or greater than 10% ester-linkage content would not fall within the literal scope of the claim unless the limitation could be established through claim construction or equivalent-substance theories.

The phrase “pharmaceutically acceptable carrier” is commercially significant. Claim 1 is directed to a pharmaceutical product rather than merely a purified chemical mixture. A bulk active ingredient without a carrier may present a noninfringement position under the literal language, although the final drug product would be the more relevant commercial article.

Claim 2: biologically active oligomer mixture

Claim 2 requires a composition that is:

Fluorescent;
Photosensitizing;
Capable of localizing in and being retained in tumor tissue relative to normal tissue;
Made of two to eight covalently linked porphyrin molecules;
Linked through ether and ester bonds;
Containing at least one porphyrin unit with the specified hydroxyethyl or vinyl substituent; and
Limited to fewer than 10% ester linkages.

Claim 2 has more structural and functional limitations than claim 1. It is potentially narrower in practice because an accused composition would need to satisfy both the molecular requirements and the stated biological characteristics.

The two-to-eight porphyrin-unit limitation is important. It excludes oligomer species outside that range if the claim is applied to the composition as a whole or to the relevant claimed oligomer population. The precise interpretation would depend on whether the limitation is read as requiring every oligomer, a material fraction, or at least one oligomer in the mixture to fall within the specified range.

Claim 3: product-by-process limitation

Claim 3 covers a porfimer sodium composition with fewer than 10% ester linkages when the oligomers are prepared by treating acetylated hematoporphyrin under alkaline conditions sufficient to achieve that result.

The claim combines:

A product limitation: porfimer sodium with fewer than 10% ester linkages; and
A process limitation: alkaline treatment of acetylated hematoporphyrin.

Under U.S. patent law, a product-by-process claim generally turns on the characteristics of the claimed product, not merely whether the accused manufacturer used the same process. A separately manufactured product with the same claimed chemical characteristics could therefore present infringement risk if the process limitation is not treated as substantively limiting in the relevant adjudication. The process language nevertheless creates evidentiary and claim-construction issues.

What do claims 4 through 7 add?

Claims 4 through 7 narrow claim 3 by specifying alkaline concentration, reagent, temperature, and time.

Claim	Added limitation
4	Alkali concentration of 0.1N to 1N
5	Sodium hydroxide; one hour at room temperature followed by 4°C for 14 to 21 days
6	Sodium hydroxide; 16 to 24 hours below 45°C
7	Sodium hydroxide at 0.1N for one hour at room temperature, followed by 0.2N to 1N for two to four hours at room temperature

These dependent claims create narrower process-defined embodiments. They would be relevant primarily where process records, batch documentation, analytical records, or manufacturing disclosures establish the conditions used.

Claim 5 describes a prolonged low-temperature treatment. Claim 6 describes a shorter elevated-temperature route. Claim 7 describes staged sodium hydroxide treatment. The alternatives suggest that the patent sought to capture multiple process routes capable of reducing ester content below the claimed threshold.

What is the technical scope of the less-than-10% ester limitation?

The less-than-10% requirement is the patent’s principal quantitative boundary.

The relevant calculation requires:

[ \text{Ester-linkage percentage} = \frac{\text{number of ester linkages}}{\text{total ester and ether linkages}} \times 100 ]

A material having 9.9% ester linkages falls within the literal numerical limitation. A material having exactly 10% does not satisfy “less than 10%.” The patent’s practical enforceability would depend on:

The analytical method used to identify ester and ether linkages;
The treatment of mixed porphyrin species;
Sampling and batch variability;
Whether the percentage is calculated on a molar, structural, or population basis; and
Whether the patent specification supplies a sufficiently reproducible measurement method.

Because porfimer sodium is a mixture, the limitation is analytically more complex than a conventional purity specification for a single small molecule. A competing manufacturer could focus on demonstrating that its product has a different oligomer distribution, a different linkage ratio, or a measurement result outside the claimed range.

What patents protect Photofrin and porfimer sodium beyond U.S. 5,438,071?

The porfimer sodium patent estate historically included multiple layers:

Protection layer	Relevance
Porphyrin chemistry	Composition and oligomer structure
Linkage distribution	Ether-to-ester ratio
Manufacturing process	Alkaline hydrolysis and conversion conditions
Pharmaceutical formulation	Carrier, dosage form, concentration, and administration
Method of treatment	Photodynamic treatment of tumors or other lesions
Regulatory exclusivity	NDA-based exclusivity separate from patent rights
International rights	Country-specific composition and process patents

U.S. Patent 5,438,071 is best understood as a composition and manufacturing patent. It is not a broad patent on every use of photodynamic therapy, every porphyrin photosensitizer, or every porfimer sodium administration protocol.

Photofrin-related protection also depended on method-of-use patents and regulatory rights. Those rights had separate expiration dates and claim requirements. A treatment patent would generally require the claimed disease, illumination protocol, dosage, or administration sequence. It would not automatically cover a competing photosensitizer or a different therapeutic indication.

When did U.S. Patent 5,438,071 lose exclusivity?

The patent expired in February 2012 under the applicable 20-year patent term calculated from its early-1990s priority and filing record. No current U.S. patent exclusivity remains under this patent.

The expiration removed the principal patent barrier created by the less-than-10% ester limitation. It also removed the practical value of claims 3 through 7 as barriers to independent manufacture using alkaline treatment, subject to any separate unexpired patents, trade secrets, regulatory controls, or contractual restrictions.

Exclusivity timeline

Event	Approximate date
Priority filing	February 1992
U.S. patent grant	August 1, 1995
Photofrin FDA approval	1995
U.S. patent expiration	February 2012
Current patent status	Expired
Current exclusivity under this patent	None

Patent expiration does not invalidate historical infringement claims arising during the enforceable term. It also does not eliminate regulatory or manufacturing barriers that are independent of the patent.

What was the Orange Book status of porfimer sodium?

Photofrin was regulated by FDA as a prescription photodynamic therapy product. FDA approved Photofrin for certain oncology indications, including esophageal cancer and non-small-cell lung cancer in specified clinical settings. FDA labeling identifies porfimer sodium as the active ingredient and describes administration followed by laser illumination. (FDA, 2011)

The Orange Book treatment of a product can change over time because of marketing status, patent listing updates, and sponsor activity. An Orange Book listing would not extend an expired patent. Any listing associated with U.S. Patent 5,438,071 would have ceased to create a current patent barrier when the patent expired.

FDA approval and patent protection are separate systems:

FDA approval establishes regulatory authorization.
Orange Book patent listing provides notice for abbreviated new drug application applicants.
Patent expiration ends the relevant patent right.
Regulatory exclusivity, if still applicable, is separate from patent term.

Photofrin is a conventional small-molecule or complex-mixture drug product for Hatch-Waxman purposes. It is not a biologic subject to the 351(k) biosimilar pathway.

Were there Paragraph IV challenges or settlements?

No material current Paragraph IV risk exists for U.S. Patent 5,438,071 because the patent expired in 2012. Any Paragraph IV certification directed to this patent would have been relevant only before expiration.

Publicly reported information does not identify a continuing U.S. litigation or settlement obligation that preserves exclusivity under this patent. A historical ANDA challenge, if filed, would not restore the patent after expiration. Any settlement could still affect launch timing during the pre-expiration period, but it would no longer block entry based on this patent.

Is porfimer sodium exposed to biosimilar competition?

No. Porfimer sodium is not a biologic under the Public Health Service Act and is not subject to biosimilar approval under section 351(k). A competing product would proceed through a small-molecule or complex-drug regulatory route, most likely requiring an abbreviated application only if FDA accepts the product as pharmaceutically and therapeutically equivalent to the reference product.

The main regulatory barriers are likely to include:

Demonstrating comparable active-ingredient composition;
Characterizing the oligomer distribution;
Establishing equivalent photosensitizing activity;
Demonstrating comparable pharmacokinetics or tissue distribution where required;
Controlling impurities and residual process materials; and
Establishing a suitable analytical method for ester and ether linkages.

The complexity of porfimer sodium may make development more difficult than a conventional single-component generic, even though the core patent has expired.

What generic launch risks exist for porfimer sodium?

A generic or competing porfimer sodium product could launch without infringing U.S. Patent 5,438,071, but commercial entry would still face technical and regulatory barriers.

Manufacturing and intellectual-property risks

The expired patent does not prevent a manufacturer from using the disclosed alkaline process. It also does not prevent a manufacturer from designing around the disclosed process by using different hydrolysis conditions, different precursor handling, or a different purification sequence.

Potential barriers include:

Proprietary control of porphyrin precursor supply;
Trade secrets concerning oligomer distribution and purification;
Difficult batch-to-batch analytical comparability;
Specialized laser and light-delivery requirements;
Limited clinical demand;
Physician familiarity with alternative photosensitizers; and
Separate unexpired patents covering formulations, devices, or treatment protocols.

Generic launch scenarios

Scenario	Commercial effect
Same or highly similar porfimer sodium composition	Patent 5,438,071 does not block launch after expiration
Different ester-linkage profile	May avoid the historical claim, but regulatory comparability becomes harder
Different porphyrin photosensitizer	Outside the patent, but requires a different clinical and regulatory strategy
Same active ingredient with a new formulation	Requires review of formulation, method, and device patents
Competing product for a different indication	May avoid Photofrin use claims but needs separate FDA support

How does this patent compare with competing photodynamic-drug estates?

Porfimer sodium differs from newer or alternative photosensitizers in both chemistry and patent risk.

Product	Active ingredient	General patent position
Photofrin	Porfimer sodium	Core U.S. composition patent expired
Visudyne	Verteporfin	Separate chemical, formulation, and use patent estate
Foscan	Temoporfin	Primarily non-U.S. commercial relevance
Talaporfin products	Talaporfin sodium	Separate composition and clinical-use rights
Photogem-type products	Porphyrin oligomer mixtures	Different regulatory and IP positions by jurisdiction

The expiration of U.S. Patent 5,438,071 does not create freedom to operate for verteporfin, temoporfin, talaporfin, or other photodynamic agents. Each product requires a separate patent and regulatory analysis.

What is the geographic scope of the patent?

U.S. Patent 5,438,071 had enforceability only in the United States. Foreign counterparts, if granted, had independent terms and claim scope. Expiration of the U.S. patent did not automatically terminate corresponding rights in Canada, Europe, Japan, or other jurisdictions.

A global launch analysis must separately review:

National-stage or priority filings;
Grant and expiration dates;
Patent-term extensions;
Supplementary protection certificates;
Local Orange Book equivalents;
Local regulatory exclusivity; and
Patent litigation or settlement records in each market.

The U.S. expiration therefore removes one national barrier, not the entire historical porfimer sodium estate.

How strong was the patent estate?

During its term, U.S. Patent 5,438,071 had commercially meaningful claim coverage because it targeted the composition associated with Photofrin and linked the product to a measurable chemical parameter. Its strength was limited by several factors:

The less-than-10% threshold created a potential design-around route.
Porfimer sodium is a heterogeneous mixture, creating analytical and claim-construction issues.
Claims 3 through 7 were tied to manufacturing conditions and could be avoided through process changes.
The patent did not cover all photodynamic agents.
The patent did not independently control every treatment method, formulation, or medical device.

Today, the estate has no blocking strength from this patent because the U.S. rights have expired. Its remaining value is historical, evidentiary, and potentially relevant to prior-art analysis.

Key Takeaways

U.S. Patent 5,438,071 centered on porfimer sodium with fewer than 10% ester linkages.
Claim 1 is a pharmaceutical composition claim requiring porfimer sodium, the linkage threshold, and a pharmaceutically acceptable carrier.
Claim 2 adds oligomer size, biological activity, structural substituents, and tumor-localization characteristics.
Claims 3 through 7 cover product-by-process embodiments using alkaline treatment of acetylated hematoporphyrin.
The patent expired in February 2012.
It creates no current U.S. patent barrier to porfimer sodium manufacture or launch.
Porfimer sodium is not subject to the biosimilar pathway.
Remaining entry barriers are primarily analytical, regulatory, manufacturing, commercial, and potentially dependent on separate patents.
A historical Paragraph IV challenge or settlement would not preserve exclusivity after expiration.
Foreign patent rights, formulation patents, treatment patents, and device patents require separate jurisdiction-specific review.

FAQs

Does U.S. Patent 5,438,071 cover all Photofrin products?

No. It covers compositions meeting the claimed porfimer sodium and linkage limitations, plus specified process-defined embodiments. It does not automatically cover every Photofrin formulation, indication, treatment protocol, or photodynamic device.

Can a company manufacture porfimer sodium using sodium hydroxide today?

Yes, U.S. Patent 5,438,071 no longer prevents use of the disclosed sodium hydroxide processes because the patent expired. Separate patents, trade secrets, regulatory requirements, and contractual restrictions must be analyzed independently.

Is a product with exactly 10% ester linkages covered by claim 1?

Not literally under the phrase “less than 10%.” Exactly 10% does not satisfy the numerical limitation, although the measurement method and claim construction would control any infringement analysis.

Does patent expiration guarantee FDA approval of a porfimer sodium generic?

No. Patent expiration removes one legal barrier but does not establish pharmaceutical equivalence, analytical comparability, clinical equivalence, manufacturing quality, or approval eligibility.

Can a competing photodynamic drug infringe this patent?

A different photosensitizer such as verteporfin or talaporfin would not ordinarily satisfy the porfimer sodium limitation. It would require a separate analysis of chemical identity, claim construction, and any other relevant patent family.

References

Food and Drug Administration. (2011). Photofrin prescribing information. U.S. Department of Health and Human Services.
U.S. Patent and Trademark Office. (n.d.). Patent term adjustment and patent term calculation guidance. U.S. Department of Commerce.
U.S. Patent No. 5,438,071. (1995). Porphyrin oligomers with reduced ester linkages. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	150968	⤷ Start Trial
Canada	2094974	⤷ Start Trial
Germany	69309340	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,438,071

Summary for Patent: 5,438,071