United States Drug Patent 6,261,546: Claim Scope, Expiration, and Acetylcholine Patent Landscape

U.S. Patent No. 6,261,546 protects a two-chamber ophthalmic acetylcholine product in which acetylcholine is kept separate from a buffered aqueous diluent until use. The strongest claims require a specific combination of lyophilized acetylcholine, mannitol, inorganic salts, sodium acetate, sterile water, and a post-mixing pH above about 5.0. The patent was issued in 2001 and its 20-year patent term expired in 2018, absent any patent-term adjustment or extension. It therefore does not currently block generic, branded, or alternative acetylcholine ophthalmic products.

What does U.S. Patent 6,261,546 protect?

The patent protects a packaging and formulation system for stabilizing acetylcholine before ophthalmic administration. Its central technical concept is separation:

A first chamber contains a buffered aqueous diluent.
A second chamber contains acetylcholine, preferably in lyophilized form.
The contents are mixed immediately before administration.
The buffer in the diluent raises or maintains the pH of the final solution at an ophthalmically acceptable level.

The claims do not broadly cover acetylcholine as an active ingredient, acetylcholine ophthalmic use generally, or every lyophilized acetylcholine formulation. They require a two-chamber or two-container configuration and a buffer located in the diluent system.

The patent is directed to the known instability problem associated with aqueous acetylcholine solutions. Acetylcholine can undergo degradation in solution, particularly when pH conditions are unfavorable. Keeping the active agent separate from the buffered diluent allows the product to be stored in a more stable form and reconstituted before intraocular use. [1]

How many independent claims does Patent 6,261,546 have?

The supplied claims contain four independent claims:

Claim	Claim category	Principal subject matter
1	Pharmaceutical product	Two-chamber product with buffered aqueous diluent and acetylcholine
12	Method of treatment	Treating an eye after specified surgery using the product of claim 1
14	Ophthalmic pharmaceutical product	Narrow formula with defined salts, sodium acetate, lyophilized acetylcholine and mannitol
15	Stabilization method	Mixing a buffered diluent with acetylcholine to produce an ophthalmically acceptable pH

Claims 2-11 and 13 depend from claim 1. Claims 16-19 depend from claim 15.

The independent product claims are the principal commercial claims. Claims 12 and 15 create separate infringement theories, but both remain tied to the claimed formulation or reconstitution process.

What are the key limitations in claim 1?

Claim 1 has five material limitations.

Two separate chambers

The product must include a first chamber and a second chamber. A single vial containing acetylcholine, buffer, salts, and water would not satisfy the literal chamber limitation.

The chambers may be implemented as:

Two separate vials;
A dual-chamber syringe;
A cartridge with a frangible seal;
A container system in which the diluent chamber and active-agent chamber remain separated until activation.

The claim does not appear limited to one particular container geometry. Its functional requirement is that the diluent and acetylcholine be separately disposed before mixing.

Buffered aqueous diluent

The first chamber must contain an aqueous diluent consisting essentially of water, inorganic salts, and at least one buffer. The phrase “consisting essentially of” generally permits components that do not materially affect the claimed buffering and ophthalmic function, while excluding components that materially change that function.

The claim therefore has a narrower excipient scope than an open-ended “comprising” formulation claim.

Acetylcholine in the second chamber

The second chamber must contain a pharmaceutically active agent comprising acetylcholine. Dependent claims narrow this to lyophilized acetylcholine and mannitol.

A product containing acetylcholine in a liquid second chamber could potentially fall within claim 1 if the other requirements are met. Claims 9-11, however, would require the lyophilized and mannitol limitations.

Buffer sufficient to control the mixed-solution pH

The buffer must be present in an amount sufficient to buffer the pH after the two chambers are mixed. This is a functional limitation. The claim does not merely require the presence of buffer; the amount must achieve the claimed post-mixing result.

Ophthalmically acceptable pH

Claim 1 requires an ophthalmically acceptable pH. Claim 2 and related claims narrow that threshold to a pH above about 5.0.

The “above about 5.0” language provides some tolerance around the numerical value. It does not necessarily require a precisely measured pH of 5.01, but a product with a final pH materially below 5.0 would face greater distance from the dependent claims.

What formulations are protected by Patent 6,261,546?

The most specific formulation appears in claims 7, 8, 10, 11 and 14.

Component	Claimed amount or description
Potassium chloride	About 0.005% to 0.10%
Magnesium chloride hexahydrate	About 0.005% to 0.10%
Calcium chloride dihydrate	About 0.005% to 0.10%
Sodium acetate	About 0.10% to 0.20% in claim 8; 0.05% to 0.50% in claim 6
Sterile water for injection	Diluent vehicle
Lyophilized acetylcholine	About 0.5% to 5%
Mannitol	About 1% to 10%
Final pH	Above about 5.0

The concentrations are stated as weight percentages based on the total weight of the mixed solution. Claim 8 also recites approximately 1 to 5 milliliters of diluent.

Claim 14 is the most commercially relevant composition claim because it combines the complete salt and buffer system with the lyophilized acetylcholine/mannitol composition. It is materially narrower than claim 1 and requires the stated concentration ranges.

How do the dependent claims narrow the patent scope?

Claims	Added limitation	Commercial significance
2, 17	Mixed pH above about 5.0	Creates a measurable final-product limitation
3	Buffer selected from acetates, borates, phosphates, carbonate, citrates or mixtures	Defines permitted buffer families
4, 18	At least one acetate or an acetate buffer	Narrows buffer chemistry
5, 6, 19	Sodium acetate at stated concentration	Targets a specific formulation approach
7, 8	Potassium, magnesium and calcium salts plus sodium acetate	Covers the defined ophthalmic diluent
9	Lyophilized acetylcholine and tonicity-adjusting agent	Narrows the active-agent chamber
10, 11	Mannitol and stated concentration ranges	Covers the principal lyophilized formulation
13	Active-agent chamber substantially free of buffer	Preserves separation of the buffering function
16	First container affixed to second container	Reaches integrated dual-container products

Claim 13 is important for design-around analysis. It reinforces the concept that the buffer is held in the diluent chamber rather than being incorporated into the acetylcholine composition.

Does claim 12 cover postoperative ophthalmic use?

Claim 12 covers administering the claim 1 product after:

Cataract surgery;
Penetrating keratoplasty; or
Iridectomy.

This is a method-of-treatment claim, not a broad claim to all ophthalmic administration. A product used for another indication would not literally satisfy the listed surgical-treatment limitation, although product claims 1 and 14 would remain relevant if their formulation and container limitations were met.

The claim is also dependent on claim 1. A postoperative acetylcholine product that lacks the claimed two-chamber architecture would not infringe claim 12 literally.

What is the manufacturing and packaging barrier created by the patent?

The patent’s principal barrier is packaging architecture rather than a difficult chemical composition alone.

A potentially relevant product would need to address:

Lyophilization of acetylcholine;
Compatibility of the active cake with mannitol;
Sterility of both chambers;
Container-closure integrity;
Controlled reconstitution;
Correct final pH after mixing;
Delivery into the eye without particulate contamination;
Stability during storage;
Validated chamber separation and activation.

A manufacturer could design around the claims by using a product that does not contain two separately disposed chambers, does not use acetylcholine, uses a different active ingredient, or does not contain the claimed buffer arrangement. A formulation with buffer in the active-agent chamber rather than the diluent chamber would require separate analysis under the specific claim language and doctrine-of-equivalents principles.

Because the patent expired, these design choices are now primarily regulatory, formulation, manufacturing and freedom-to-operate decisions rather than responses to an enforceable exclusion right under Patent 6,261,546.

When did U.S. Patent 6,261,546 lose exclusivity?

The patent issued on July 17, 2001. Its ordinary U.S. patent term ran for approximately 20 years from the relevant nonprovisional filing date and expired in 2018. [1] The patent is therefore expired and cannot support a current injunction or damages claim for post-expiration conduct.

A patent expiration date is distinct from FDA regulatory exclusivity. Patent 6,261,546 does not create current regulatory exclusivity for acetylcholine ophthalmic products.

What is the FDA and Orange Book status of the protected product?

The commercial product associated with this technology is Miochol-E, an intraocular acetylcholine chloride product marketed by Novartis/Alcon-related entities over different periods. FDA labeling describes a sterile lyophilized acetylcholine chloride product reconstituted with a supplied diluent before intraocular administration. The labeled surgical uses include induction of miosis during cataract surgery and other ophthalmic procedures. [2]

The regulatory position is distinct from the patent position:

Issue	Status
FDA approval	Acetylcholine ophthalmic products have an established FDA approval history
Patent 6,261,546	Expired in 2018
Current patent barrier from 6,261,546	None
Regulatory exclusivity from this patent	None
Orange Book effect	Any historical listing does not extend an expired patent
Generic pathway	Potential ANDA or other applicable FDA pathway, subject to product-specific requirements

The Orange Book lists patents and exclusivity associated with approved drug products. It does not revive expired patents or create a new exclusivity period. [3]

Are there Paragraph IV challenges to Patent 6,261,546?

A current Paragraph IV challenge to this patent would have no practical blocking effect because the patent has expired. Paragraph IV certifications are relevant when an ANDA applicant seeks approval before expiration of an Orange Book-listed patent. [4]

Any historical Paragraph IV certification, patent litigation or settlement involving an acetylcholine product would now be commercially limited unless it concerned a separate unexpired patent, contractual restriction or regulatory issue. The expired patent cannot support a new 30-month stay based solely on Patent 6,261,546.

What patent litigation affects acetylcholine ophthalmic products?

Patent 6,261,546 is no longer an enforceable litigation barrier. Litigation risk may still arise from:

Later patents covering container systems;
New formulations of acetylcholine chloride;
Sterile manufacturing processes;
Delivery devices;
Combination products;
Trade dress or packaging claims;
Trademark rights associated with Miochol-E;
Regulatory exclusivity or approval disputes.

No conclusion that a current product is clear of all third-party rights follows solely from expiration of Patent 6,261,546. The patent removes one historical patent layer, not every possible later right.

How strong is the patent estate for acetylcholine ophthalmic products?

Patent 6,261,546 was commercially focused but technically narrow. Its strongest features were:

The two-chamber configuration;
Buffer placement in the diluent;
Final pH control after mixing;
The defined salt and sodium acetate system;
Lyophilized acetylcholine with mannitol.

Its weaknesses for present-day enforcement are:

Expiration in 2018;
Dependence on a specific container architecture;
Functional pH language that may require testing;
Narrow concentration ranges in the most specific claims;
Surgical-use limits in claim 12;
Lack of current enforceability.

For a generic or alternative manufacturer, the patent is historically relevant to product design but does not present a live exclusion right. The primary commercial risks are FDA approval, aseptic processing, reconstitution performance, stability, and supply reliability.

How does this patent compare with broader drug patents?

Patent type	Breadth	Relevance to acetylcholine competition
Active-ingredient patent	Broad chemical protection	Not the focus of Patent 6,261,546
Composition patent	Protects ingredients and concentrations	Present in claims 7, 8, 11 and 14
Container or device patent	Protects chamber architecture	Central to claims 1 and 16
Method-of-use patent	Protects administration for a specified indication	Claim 12
Manufacturing patent	Protects lyophilization or sterile processing	Not expressly claimed in the supplied claims
Stabilization patent	Protects storage and reconstitution approach	Claims 15-19

Patent 6,261,546 is best characterized as a formulation-packaging and stabilization patent with a limited method-of-use component.

Key Takeaways

U.S. Patent 6,261,546 protects a two-chamber acetylcholine ophthalmic product.
The diluent chamber must contain water, inorganic salts and buffer.
The active chamber must contain acetylcholine; dependent claims specify lyophilized acetylcholine and mannitol.
The most specific claims target potassium chloride, magnesium chloride hexahydrate, calcium chloride dihydrate, sodium acetate and sterile water.
The mixed solution must reach an ophthalmically acceptable pH, with dependent claims requiring a pH above about 5.0.
Claim 12 covers postoperative use after cataract surgery, penetrating keratoplasty or iridectomy.
The patent expired in 2018 and does not currently block generic or competing acetylcholine ophthalmic products.
Any current freedom-to-operate review must focus on later formulation, device, manufacturing, trademark and regulatory rights.

FAQs

Does Patent 6,261,546 cover Miochol-E?

The claimed two-chamber, lyophilized acetylcholine and buffered-diluent architecture corresponds closely to the type of product described in historical Miochol-E labeling. The patent is expired, so it no longer provides enforceable exclusivity over the product configuration.

Can a generic acetylcholine ophthalmic product launch after patent expiration?

Patent expiration removes the blocking effect of Patent 6,261,546. FDA approval, bioequivalence or other applicable approval requirements, sterility validation, manufacturing controls and any later unexpired patents remain relevant.

Is acetylcholine itself still patent-protected in the United States?

Patent 6,261,546 does not claim acetylcholine as a chemical compound. It claims a particular product, formulation, container and stabilization arrangement. Expiration of this patent does not determine the status of unrelated patents.

Does a different buffer avoid the patent?

A different buffer may avoid claims limited to acetate or sodium acetate, but claim 1 broadly recites at least one buffer. A non-acetate formulation would require analysis against the broad independent claim and its pH and chamber limitations.

Does a single-vial liquid formulation infringe claim 1?

A single-vial product generally lacks the required first and second chambers. It would not literally satisfy the central two-chamber limitation, although the complete product and patent history would control any broader infringement analysis.

References

United States Patent and Trademark Office. (2001). U.S. Patent No. 6,261,546, pharmaceutical product comprising acetylcholine and buffered diluent.
U.S. Food and Drug Administration. (n.d.). Miochol-E acetylcholine chloride for intraocular solution: Prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
United States Code. (2023). 21 U.S.C. § 355(j): Abbreviated applications and patent certifications.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	286380	⤷ Start Trial
Australia	4034099	⤷ Start Trial
Australia	745124	⤷ Start Trial
Brazil	9910077	⤷ Start Trial
Canada	2327398	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,261,546

Summary for Patent: 6,261,546