United States Patent 6,074,666: Scope, Claim Analysis, Expiration, and Patent Landscape for Liposomal Verteporfin

U.S. Patent 6,074,666 protects a specific liposomal delivery system for benzoporphyrin derivative photodynamic therapy, particularly verteporfin, also known as BPD-MA. The patent is formulation-focused. It does not broadly claim verteporfin, photodynamic therapy, or every liposomal photosensitizer formulation.

The patent reached its ordinary 20-year term in 2016 and is no longer an enforceable exclusionary right. Its historical importance is tied to Visudyne, the verteporfin product developed by QLT and commercialized through Novartis and later Bausch + Lomb. Current competition depends primarily on FDA approval, manufacturing capability, drug-substance and formulation know-how, and any surviving patents outside this expired patent family.

What does U.S. Patent 6,074,666 protect?

The patent protects a liposomal pharmaceutical formulation containing four principal technical elements:

A liposomal bilayer.
Dimyristoyl phosphatidylcholine, or DMPC.
Egg phosphatidylglycerol, or EPG.
A porphyrin macrocycle photosensitizer.

The claims narrow the formulation further to hydromonobenzoporphyrins absorbing light between 670 and 780 nanometers, specific BPD compounds, verteporfin, optional sugars, freeze-drying, reconstitution, defined component ratios, and selected antioxidants.

The commercial relevance is strongest for BPD-MA, the active photosensitizer associated with verteporfin and Visudyne.

Patent identification and status

Item	Information
U.S. patent	6,074,666
Title	Liposomal formulations of benzoporphyrin derivative
Technology	Liposomal photodynamic therapy formulations
Original applicant or assignee	QLT-related entity, identified in public patent records as QLT Phototherapeutics, Inc.
U.S. issue date	June 13, 2000
Priority chain	1995-era priority filings
Patent term	Ordinary 20-year term from the applicable U.S. nonprovisional filing
Expiration	2016
Current enforceability	Expired
Principal product association	Verteporfin, marketed as Visudyne
FDA product type	Small-molecule injectable photodynamic therapy drug
Biosimilar pathway	Not applicable

The patent’s expiration removes infringement risk under this patent. It does not remove regulatory requirements for a competing verteporfin product.

How broad is claim 1?

Claim 1 is the principal composition claim. It requires a liposomal formulation comprising:

A bilayer;
DMPC;
Egg phosphatidylglycerol; and
A porphyrin macrocycle photosensitizer.

The phrase “consists essentially of” limits the claim differently from “comprises” and “consists of.” It permits additional ingredients that do not materially alter the basic and novel characteristics of the claimed bilayer. The formulation therefore may tolerate excipients, stabilizers, buffers, or other minor components, but an accused product containing a materially different membrane system could fall outside the claim.

The claim is narrower than a claim to:

Any liposomal photosensitizer;
Any verteporfin formulation;
Any phospholipid vesicle;
Any photodynamic therapy composition; or
Any formulation containing DMPC alone.

A competing formulation using hydrogenated phosphatidylcholine, distearoyl phosphatidylcholine, synthetic phosphatidylglycerol, or a nonliposomal vehicle would require separate analysis and would not literally satisfy all components of claim 1.

Claim 1 element analysis

Claim element	Scope implication
“Liposomal formulation”	Requires a vesicular lipid delivery system, not a simple solution or suspension
“Bilayer”	Requires a lipid membrane structure
“Consists essentially of”	Allows non-material additional components but restricts material changes to the claimed system
DMPC	Requires dimyristoyl phosphatidylcholine
Egg phosphatidylglycerol	Requires the specified egg-derived phospholipid or an equivalent construction supported by the patent record
Porphyrin macrocycle photosensitizer	Covers a class broader than BPD-MA, but dependent claims narrow the class

What do claims 2 through 4 protect?

Claims 2 through 4 narrow the photosensitizer.

Claim 2 requires a hydromonobenzoporphyrin with a light absorption maximum between 670 and 780 nanometers. This limitation excludes porphyrins that do not satisfy the hydromonobenzoporphyrin structural requirement or the specified absorption range.

Claim 3 identifies four compounds:

BPD-DA;
BPD-DB;
BPD-MA; and
BPD-MB.

Claim 4 narrows the formulation to BPD-MA with carbomethoxy substituents and a methyl group. This is the claim most directly associated with verteporfin formulations.

A product containing a different photosensitizer could avoid claims 3 and 4 but might still require analysis under claims 1 or 2, depending on the molecule and the formulation.

Commercial relevance of BPD-MA

BPD-MA is the key commercial species because verteporfin is a benzoporphyrin derivative used in photodynamic therapy. Visudyne is supplied as a sterile lyophilized product that is reconstituted before administration, making claims 5 through 9 technically relevant to the commercial dosage form. [2]

What do claims 5 through 9 protect?

These claims address stabilization and presentation of the liposomal product.

Claim 5 adds one or more sugars.
Claim 6 limits the sugar to a disaccharide.
Claim 7 identifies lactose or trehalose.
Claim 8 requires a freeze-dried formulation.
Claim 9 covers the freeze-dried formulation after reconstitution with an aqueous pharmaceutical fluid.

These claims are directed to a lyophilized product architecture rather than merely the active drug. They may be relevant to a generic or follow-on manufacturer using the same excipient strategy and presentation.

The claims do not cover every freeze-dried verteporfin product. The product must still satisfy the underlying DMPC, egg phosphatidylglycerol, and porphyrin limitations inherited from the preceding claims.

Formulation risk by product design

Competing design	Likely relevance to claims 5-9
Same DMPC/egg phosphatidylglycerol system with trehalose	High historical relevance
Same lipid system with lactose	High historical relevance
Same lipid system with sucrose	Potentially within claim 5, but not claims 6-7
Liquid formulation without freeze-drying	Potentially claim 5, not claims 8-9
Nonliposomal verteporfin solution	Outside the literal liposome claims
Liposome using a different lipid pair	May avoid literal infringement, subject to claim construction and equivalents
Freeze-dried liposome using mannitol only	Potentially outside the sugar limitations, depending on the full formulation

What do claims 10 through 12 protect?

Claim 10 specifies relative weight ratios for the photosensitizer and the two lipids:

Porphyrin: approximately 0.2 to 0.4;
DMPC: approximately 0.94 to 1.88;
Egg phosphatidylglycerol: approximately 0.65 to 1.30.

Claim 11 adds sugar and specifies:

Disaccharide: approximately 8.0 to 12.0 parts; or
Monosaccharide: approximately half that amount.

Claim 12 adds butylated hydroxytoluene, or BHT, or ascorbyl palmitate.

These are narrow formulation claims. They are useful against products that reproduce the patented formulation design but provide less coverage against materially different lipid ratios, stabilizers, or manufacturing approaches.

Ratio limitations and infringement

The use of “about” gives the claims tolerance around the stated numerical ranges. The scope depends on ordinary claim construction, specification support, prosecution history, and potentially expert evidence. A product just outside a numerical range could still raise an equivalents issue, although the prosecution history may restrict that argument.

A manufacturer cannot avoid claim 10 merely by changing the batch size. The relevant comparison is the relative amount of each component, not the absolute quantity per vial.

Does the patent cover a method of treating disease?

No. The supplied claims are composition claims. They do not claim:

Treating age-related macular degeneration;
Treating choroidal neovascularization;
Treating pathological myopia;
Treating ocular histoplasmosis;
Administering verteporfin with a specified laser protocol; or
A particular treatment schedule.

The patent therefore does not independently create a method-of-use monopoly for photodynamic therapy. Any method-of-use protection would have to arise from separate patents or regulatory exclusivity.

This distinction matters because a manufacturer could face no live infringement risk under Patent 6,074,666 while still needing to assess separate method patents, product patents, or FDA labeling restrictions.

When did U.S. Patent 6,074,666 lose exclusivity?

The patent lost enforceable patent exclusivity in 2016 after expiration of its ordinary 20-year term. Patent expiration is distinct from:

FDA approval;
FDA marketing exclusivity;
Orange Book listing;
Drug-product approval;
Patent-term extension; and
Regulatory review periods.

No current patent right under Patent 6,074,666 should block manufacture, sale, or importation of a formulation that would otherwise have been covered by the expired claims.

The patent’s expiration also means that a new entrant does not need a license from the former patent owner to practice the claimed liposomal formulation. A license could still be commercially useful for manufacturing know-how, technical data, trademarks, or supply arrangements, but it is not required to practice an expired patent.

What was the Orange Book status of Visudyne?

Visudyne was approved by the FDA as verteporfin for injection under NDA 021119. The product is a small-molecule drug, not a biologic. FDA Orange Book treatment therefore differs from the Purple Book framework used for biologics and biosimilars. [2, 3]

Historically, patents associated with the active ingredient, formulation, or approved use could be listed in the Orange Book if they met FDA listing requirements. Patent 6,074,666 was relevant to the commercial formulation landscape, but its expiration means it no longer creates an active patent barrier.

An Orange Book listing does not extend patent term. It also does not establish that every formulation of verteporfin infringes the listed patent. The listing identifies patent rights asserted to cover the approved drug, its formulation, or an approved method of use.

What Paragraph IV challenges and generic-entry risks exist?

A Paragraph IV certification is used when an ANDA applicant asserts that a listed patent is invalid, unenforceable, or not infringed. For Patent 6,074,666, a current Paragraph IV challenge would have limited commercial value because the patent expired in 2016.

The relevant historic risk profile was different. Before expiration, an ANDA applicant seeking to reproduce the Visudyne formulation could have faced:

A patent certification requirement;
Potential Hatch-Waxman litigation;
A 30-month stay if a timely infringement action was filed;
Formulation-specific design-around work; and
Difficulty demonstrating pharmaceutical equivalence for a complex liposomal product.

Today, the main generic-entry barriers are regulatory and technical:

Demonstrating pharmaceutical equivalence;
Matching liposome size, composition, loading, and release characteristics;
Establishing stability after lyophilization and reconstitution;
Reproducing the photosensitizer’s purity profile;
Validating sterile manufacturing;
Demonstrating bioequivalence or an FDA-accepted alternative pathway; and
Securing reliable supply of BPD-MA and specialized phospholipids.

There is no biosimilar risk analysis for verteporfin because verteporfin is a chemically synthesized small molecule rather than a biological product.

Which companies are associated with Visudyne and its patent estate?

Company	Role
QLT Phototherapeutics and related QLT entities	Inventor-originator and early patent owner or applicant associated with verteporfin technology
Novartis	Commercial partner and historical global marketer of Visudyne
Bausch + Lomb	Later commercial owner or marketer in certain markets after acquisition of relevant ophthalmic assets
Generic applicants	Potential competitors subject to FDA approval and formulation equivalence requirements

Commercial rights and patent ownership are separate questions. The party selling Visudyne may not be the current owner of every historical patent. Patent assignment records, corporate transactions, and country-specific licenses control ownership and enforcement rights. [1, 4]

How strong is the patent estate for this formulation?

The patent was technically strong while active but narrow in claim architecture.

Strengths

It identified the specific DMPC and egg phosphatidylglycerol bilayer used for a commercially important liposomal photosensitizer.
It covered BPD-MA, the most commercially relevant compound.
It included lyophilized and reconstituted presentations.
It included sugar and antioxidant embodiments.
It provided numerical composition ranges that could support product-specific enforcement.

Weaknesses

The claims were not directed to verteporfin generally.
They did not cover all liposomal delivery systems.
They did not claim treatment methods.
The “consists essentially of” language may permit design-around through materially different lipid systems.
The numerical claims could be avoided through formulation optimization outside the claimed ranges.
The patent expired in 2016.

The estate is therefore historically important but has no current blocking value by itself.

What manufacturing and intellectual-property barriers remain?

The expired patent does not eliminate practical barriers to competition. The most important surviving barriers are likely to be technical rather than patent-based:

Drug substance production. BPD-MA synthesis, purification, impurity control, and scale-up require specialized chemistry.
Liposome engineering. Particle size, encapsulation, aggregation, leakage, and storage stability affect product performance.
Lyophilization. The freeze-drying cycle must preserve liposome integrity and permit reproducible reconstitution.
Sterile manufacture. Injectable liposomal products require validated aseptic processing or terminal sterilization where feasible.
Analytical characterization. Conventional small-molecule assays may not fully establish equivalence for a complex liposomal product.
Clinical and regulatory strategy. FDA may require comparative quality, pharmacokinetic, pharmacodynamic, or clinical data depending on the proposed abbreviated pathway.
Trade secrets. Manufacturing parameters, mixing conditions, filtration procedures, and reconstitution specifications may remain valuable even after patent expiration.

What generic launch scenarios exist?

Scenario	Commercial outcome
Same lipid system and same excipients	Patent 6,074,666 is no longer a barrier, but FDA equivalence and manufacturing remain difficult
Lipid design-around	Lower historical patent exposure, but potentially higher development cost
Nonliposomal verteporfin	May avoid the expired claims but could fail to reproduce clinical performance
Authorized generic or licensed supply	Faster market access if commercial rights and supply are available
New photodynamic therapy agent	Competes clinically but does not directly substitute for verteporfin without matching indication and workflow
Compounded or off-label product	Does not provide an FDA-approved generic substitute for Visudyne

Key Takeaways

U.S. Patent 6,074,666 claims a specific liposomal formulation for porphyrin photodynamic therapy.
The most commercially important embodiment is a DMPC and egg phosphatidylglycerol liposome containing BPD-MA, or verteporfin.
Claims 5 through 9 focus on sugars, lactose or trehalose, lyophilization, and reconstitution.
Claims 10 and 11 impose narrow component-ratio limitations.
Claim 12 adds BHT or ascorbyl palmitate as an antioxidant embodiment.
The patent does not claim verteporfin generally or a method of treating macular disease.
The patent expired in 2016 and no longer creates an enforceable patent barrier.
Verteporfin is a small-molecule drug, so biosimilar analysis does not apply.
Current competition is more likely to turn on FDA approval, pharmaceutical equivalence, sterile liposome manufacturing, drug-substance supply, and trade secrets than on this expired patent.

FAQs

Is verteporfin still protected by U.S. Patent 6,074,666?

No. Patent 6,074,666 expired in 2016. Its claims remain relevant for historical claim analysis but cannot presently be enforced as an unexpired U.S. patent.

Does the patent cover every liposomal verteporfin product?

No. The claims require the specified DMPC and egg phosphatidylglycerol bilayer and, in narrower claims, specific BPD compounds, sugars, ratios, and antioxidants.

Can a generic manufacturer use trehalose in a verteporfin liposome?

The use of trehalose would have been directly relevant to claims 6 and 7 while the patent was active. The patent’s expiration removes that patent obstacle, but the manufacturer must still satisfy FDA requirements.

Is Visudyne subject to biosimilar competition?

No. Verteporfin is a small-molecule drug. A competing product would generally proceed through an abbreviated or full new-drug pathway rather than the biosimilar pathway.

Are method-of-use patents included in Patent 6,074,666?

No. The supplied claims are directed to liposomal compositions and formulation characteristics. They do not claim a treatment method, laser protocol, disease indication, or dosing regimen.

References

United States Patent and Trademark Office. (2000). U.S. Patent No. 6,074,666: Liposomal formulations of benzoporphyrin derivative.
U.S. Food and Drug Administration. (2000). Visudyne (verteporfin for injection) prescribing information.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book.
Novartis AG. (Various years). Annual reports and product information concerning Visudyne and ophthalmic pharmaceutical assets.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	151984	⤷ Start Trial
Canada	2087902	⤷ Start Trial
Germany	69310014	⤷ Start Trial
Denmark	0569113	⤷ Start Trial
European Patent Office	0569113	⤷ Start Trial
Spain	2100452	⤷ Start Trial
Greece	3023906	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,074,666

Summary for Patent: 6,074,666