United States Patent 6,316,443: Scope, Claims, Expiration, and Ophthalmic Combination Patent Landscape

U.S. Patent No. 6,316,443 protects ophthalmic combinations containing a topical carbonic anhydrase inhibitor and a beta-adrenergic antagonist for treating ocular hypertension. Its commercial center is the dorzolamide/timolol combination marketed as Cosopt. The patent covers drug concentrations, specific inhibitor substituents, timolol and betaxolol combinations, treatment methods, and formulations containing gellan gum.

The patent is no longer an active barrier to generic entry. Its value today is historical and analytical: it explains the original combination strategy, the formulation architecture of Cosopt, and the scope that generic applicants would have had to address through Paragraph IV certifications or post-expiration ANDA pathways.

What does U.S. Patent 6,316,443 protect?

U.S. Patent 6,316,443 protects a topical ophthalmic combination comprising:

Component	Claimed range or requirement
Carbonic anhydrase inhibitor	0.5% to 5.0% w/w
Beta-adrenergic antagonist	0.01% to 1.0%
Carbonic anhydrase inhibitor examples	Dorzolamide-related and brinzolamide-related sulfonamide structures
Beta blocker examples	Betaxolol, bufenolol, carteolol, levobunolol, metipranolol, or timolol
Administration	Topical ocular administration
Indication	Ocular hypertension, including pressure inadequately controlled by beta blockers
Optional excipient	0.1% to 2.0% gum, including gellan gum
Narrower ratio limitation	Carbonic anhydrase inhibitor concentration greater than beta-blocker concentration

The patent has three principal claim categories:

Combination ophthalmic formulations.
Methods of treating ocular hypertension using those formulations.
Narrower formulations containing a specified carbonic anhydrase inhibitor, timolol or betaxolol, and a carbonic anhydrase inhibitor-to-beta blocker ratio greater than one.

The patent does not claim every possible glaucoma formulation. Its claims require a carbonic anhydrase inhibitor within the defined chemical genus and a beta-adrenergic antagonist within the recited list.

Which commercial drugs fall within the patent claims?

The principal commercial product associated with the patent is Cosopt, a fixed-dose ophthalmic solution containing dorzolamide hydrochloride and timolol maleate. The original Cosopt formulation contains approximately 2% dorzolamide hydrochloride and 0.5% timolol, placing it within the concentration ranges of claims 1, 4, 7, 10, 13, and 15.[1]

Dorzolamide

Dorzolamide is the clearest commercial compound within the claimed genus. The claim limitations corresponding to the commercial molecule include:

A as carbon;
Z as NHR;
X as SO2;
R as ethyl;
R1 as methyl.

That combination is expressly reflected in claims 3, 6, 14, and 16. A formulation containing approximately 2% dorzolamide and 0.5% timolol also satisfies the greater-than-one concentration ratio in claim 15.

Brinzolamide and related inhibitors

The claims are not limited to dorzolamide. Their chemical definitions cover additional sulfonamide carbonic anhydrase inhibitors, including structures associated with brinzolamide-type chemistry and related analogues.

The breadth comes from the Markush limitations covering:

Carbon or nitrogen at position A;
NHR or OR at position Z;
Straight-chain or branched C1-C6 alkyl groups;
Hydrogen, C1-C3 alkyl, or C1-C4 alkoxy-C1-C4 alkyl at R1;
Sulfonyl or carbonyl linkage at X;
Individual diastereomers, individual enantiomers, mixtures, and ophthalmologically acceptable salts.

A generic product containing brinzolamide rather than dorzolamide would not automatically infringe. It would need to satisfy the structural limitations and the beta-blocker, concentration, and formulation requirements of at least one unexpired claim. Because the patent has expired, this distinction now has limited market-entry significance but remains relevant to historical claim analysis.

How do the claims divide by scope?

Claims 1 to 9: Formulation claims

Claim 1 is the broad independent formulation claim. It requires:

An ophthalmologically acceptable carrier;
0.5% to 5% carbonic anhydrase inhibitor;
0.01% to 1.0% beta blocker;
Treatment of ocular hypertension in a patient inadequately controlled by beta-adrenergic antagonists.

Claims 2 and 3 narrow the carbonic anhydrase inhibitor structure. Claim 4 limits the beta blocker to timolol. Claim 5 separately covers betaxolol.

Claims 6 and 7 impose narrower substituent and concentration limitations. Claim 8 adds a gum at 0.1% to 2.0%, and claim 9 identifies gellan gum.

Claim 9 is particularly important from a formulation perspective because it moves beyond the active ingredients and claims a viscosity-modifying or suspension-stabilizing excipient strategy. A formulation using the claimed drug combination but omitting gellan gum could fall outside claim 9 while remaining within broader claims.

Claims 10 to 14: Method-of-treatment claims

Claim 10 covers topical ocular administration of the claimed combination to a patient requiring treatment for ocular hypertension.

Claim 11 narrows the beta blocker to timolol or betaxolol and limits the carbonic anhydrase inhibitor substituents. Claim 12 narrows the core structure to carbon, NHR, and SO2. Claims 13 and 14 further select timolol and specific substituent combinations.

These claims are method claims, not product claims. Their commercial relevance depends on the jurisdiction's treatment of induced infringement and the labeling of a generic product. A generic label expressly indicating use for ocular hypertension would historically have created greater method-of-use exposure than a label omitting the patented indication.

Claims 15 to 17: Ratio, active-ingredient, and gellan-gum claims

Claim 15 is a narrower independent formulation claim. It requires:

Carbon as A;
NHR as Z;
C1-C6 alkyl at R;
C1-C3 alkyl at R1;
SO2 as X;
Timolol or betaxolol;
A carbonic anhydrase inhibitor-to-beta blocker ratio greater than one.

Claim 16 narrows the inhibitor to the R = ethyl and R1 = methyl combination associated with dorzolamide.

Claim 17 adds gellan gum at approximately 0.1% to 2.0%.

The commercial 2% dorzolamide/0.5% timolol composition has a 4:1 concentration ratio and therefore fits the numerical ratio limitation in claim 15.

What are the key claim-construction issues?

The main claim-construction questions concern chemical identity, concentration measurement, salts, and formulation equivalence.

Chemical genus versus named active ingredient

The claims do not name dorzolamide in the body of the claims. They define a chemical genus by structural variables. A product analysis therefore requires mapping the active ingredient to each variable:

Claim variable	Key issue
A	Carbon or nitrogen
Z	NHR or OR
R	C1-C6 straight or branched alkyl
R1	Hydrogen, C1-C3 alkyl, or alkoxyalkyl
X	SO2 or carbonyl
Stereochemistry	Individual diastereomers, enantiomers, or mixtures
Salt form	Ophthalmologically acceptable salts included

This structure creates potentially broad coverage around the preferred sulfonamide series while preserving narrower protection for specific substituent combinations.

Concentration ranges

The broad claims require 0.5% to 5% carbonic anhydrase inhibitor and 0.01% to 1.0% beta blocker. A product outside either range would avoid literal infringement of the corresponding claim, subject to prosecution history and equivalents analysis.

The ratio claim is separate. A product could satisfy the concentration ranges of claim 1 but fail claim 15 if the carbonic anhydrase inhibitor concentration is not greater than the beta-blocker concentration.

Salt forms

The claims expressly include ophthalmologically acceptable salts. This prevents a generic applicant from avoiding the claims merely by using a different pharmaceutically acceptable salt of the same active moiety.

Gellan gum

Gellan gum is not required by claims 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, or 16. It is required only by claims 9 and 17. The gellan gum limitation therefore has narrower infringement reach but may have been relevant to formulation design and regulatory comparability.

When did U.S. Patent 6,316,443 lose exclusivity?

U.S. Patent 6,316,443 is expired and does not provide a current U.S. patent-based barrier to generic dorzolamide/timolol entry.

Patent expiration must be determined from the effective nonprovisional filing date, applicable patent-term adjustment, and any terminal disclaimer or patent-term extension. The patent's term has ended under the standard 20-year patent-term framework. The patent is therefore not a current Orange Book exclusivity asset.[2][3]

The patent's expiration does not eliminate other potential barriers associated with:

Separate compound patents;
Formulation patents;
Later patents for preservative-free products;
Manufacturing processes;
Device or container systems;
Regulatory exclusivity;
Trade secrets and supplier arrangements.

Those rights must be evaluated independently from Patent 6,316,443.

What was the Orange Book status of the patent?

Patent 6,316,443 was associated with the Cosopt dorzolamide hydrochloride/timolol maleate ophthalmic product. Orange Book analysis for a fixed-dose ophthalmic product generally separates:

Drug-substance patents;
Drug-product or formulation patents;
Method-of-use patents;
Regulatory exclusivity.

The patent's claim language is principally directed to drug-product combinations and methods of treatment. It is not a patent on timolol alone or dorzolamide alone.

The FDA's Orange Book is the controlling source for current listed-patent status, expiration, and delisting information. Because Patent 6,316,443 is expired, a current applicant would not face a live patent term from this patent, although the patent could have been central to earlier ANDA certifications.[2]

Which generic entry risks did the patent create?

Before expiration, the patent created several Paragraph IV risk categories under the Hatch-Waxman Act.

Product infringement risk

A generic fixed-dose solution containing:

Dorzolamide at approximately 2%;
Timolol at approximately 0.5%;
A pharmaceutically acceptable carrier;

would have closely tracked the core formulation limitations.

Method-of-use risk

A generic applicant could face method claims if its labeling instructed treatment of ocular hypertension using the covered combination. Label carve-outs could reduce risk where the patented indication was separable from noninfringing uses.

Formulation risk

A product containing gellan gum could have implicated claims 8, 9, or 17. A product using another viscosity modifier or suspending agent would require a separate claim analysis.

Chemical-structure risk

A product containing a different carbonic anhydrase inhibitor could avoid claims tied to the narrower R and R1 combinations but still face claim 1 or claim 10 if the alternative molecule remained within the broader Markush structure.

What patent litigation and settlement issues affected the product?

The principal litigation exposure would have arisen when an ANDA applicant filed a Paragraph IV certification against a listed patent covering the dorzolamide/timolol combination. The statutory framework permits the patent owner to sue within 45 days of receiving notice, triggering a potential 30-month stay of approval under 21 U.S.C. § 355(j).[4]

The typical disputes for this patent would have involved:

Whether the proposed product satisfied the structural Markush limitations;
Whether the claimed concentration ranges were met;
Whether the patent was obvious in view of separate dorzolamide and timolol products;
Whether the combination produced unexpected therapeutic or tolerability benefits;
Whether the method claims were properly carved out;
Whether gellan gum was present in the proposed formulation.

A current commercial assessment should not treat old Paragraph IV litigation or settlement terms as a live exclusivity right. Any settlement would need to be reviewed for its agreed launch date, authorized generic provisions, manufacturing restrictions, and scope of released claims.

How strong was the patent estate?

The estate was strongest against a generic that copied the commercial Cosopt architecture:

Risk factor	Assessment
Dorzolamide plus timolol	High historical claim overlap
Approximately 2%/0.5% concentrations	High overlap
Carbonic anhydrase inhibitor concentration greater than beta blocker	Directly aligned with claim 15
Gellan gum-containing formulation	Additional, narrower claim exposure
Betaxolol combination	Covered by claims 5, 10, 11, and 15
Alternative beta blocker	Potential coverage under claim 1 or claim 10
Brinzolamide combination	Requires detailed structural mapping
Different concentration profile	Potential design-around
Separate, nonclaimed excipient system	Avoids only gellan-gum claims
Current blocking strength	None, because the patent is expired

The patent was commercially meaningful because it combined broad active-ingredient coverage with concentration limitations and narrower formulation fallbacks. Its weakness was that it did not create perpetual control over the individual active ingredients. Competitors could pursue different inhibitor structures, concentrations, excipients, or delivery systems.

How does this patent compare with compound and formulation patents?

Patent 6,316,443 is a combination patent. It differs from the surrounding patent categories as follows:

Patent category	Typical subject matter	Relationship to 6,316,443
Carbonic anhydrase inhibitor compound patent	Dorzolamide or brinzolamide molecule	Earlier or separate active-ingredient protection
Timolol compound patent	Beta blocker molecule and salts	Separate active-ingredient protection
Combination patent	Carbonic anhydrase inhibitor plus beta blocker	Core subject of 6,316,443
Formulation patent	Preservative, viscosity modifier, pH, stability, or delivery system	May overlap only with claims 8, 9, or 17
Method patent	Treatment of ocular hypertension or glaucoma	Claims 10 to 14
Manufacturing patent	Synthesis, crystallization, salt formation, or sterile filling	Outside the principal scope of 6,316,443
Device patent	Container, dropper, multidose valve, or preservative-free package	Separate rights

This distinction matters in freedom-to-operate work. Expiration of the combination patent does not establish freedom from every patent affecting a generic ophthalmic product.

Does biosimilar law apply to this patent?

No. Dorzolamide, timolol, betaxolol, and related ophthalmic products are small-molecule drugs, not biologics. Biosimilar pathways under section 351(k) of the Public Health Service Act do not apply.

Generic applicants use the ANDA pathway under section 505(j) of the Federal Food, Drug, and Cosmetic Act. Relevant issues include pharmaceutical equivalence, bioequivalence, inactive ingredients, microbiological quality, sterility, container closure, and labeling.[4][5]

What manufacturing and geographic barriers remain?

The patent is a U.S. right. Its expiration does not affect corresponding foreign rights, which must be assessed country by country.

Potential non-patent barriers include:

Sterile ophthalmic manufacturing capacity;
Validated preservative and microbial-control systems;
Consistent particle size and solubility for the active ingredient;
Container-closure compatibility;
Drop-size control;
Stability under storage conditions;
Supply of pharmaceutical-grade dorzolamide or equivalent inhibitor;
Regulatory comparability for viscosity, pH, osmolality, and preservative content.

Manufacturing process patents may remain relevant even when the combination patent has expired. Trade-secret synthesis routes and supplier exclusivity can also affect launch timing without appearing in the Orange Book.

Key Takeaways

U.S. Patent 6,316,443 covers ophthalmic combinations of a defined carbonic anhydrase inhibitor genus with specified beta blockers.
The patent's commercial focus is the dorzolamide/timolol combination marketed as Cosopt.
The core commercial concentration profile, approximately 2% dorzolamide and 0.5% timolol, falls within the principal formulation claims.
Claims 10 to 14 cover topical treatment methods for ocular hypertension.
Claims 8, 9, and 17 add gellan gum limitations.
Claim 15 adds a carbonic anhydrase inhibitor-to-beta blocker ratio greater than one.
The patent includes salts, stereoisomers, and mixtures within its structural scope.
The patent has expired and is not a current U.S. exclusivity barrier.
Biosimilar law is irrelevant; the relevant regulatory pathway is ANDA approval.
Current freedom-to-operate analysis must separately review later formulation, manufacturing, device, and foreign patents.

FAQs

What drug is most directly associated with U.S. Patent 6,316,443?

Dorzolamide hydrochloride/timolol maleate ophthalmic solution, marketed as Cosopt, is the principal commercial product associated with the patent.

Does the patent cover dorzolamide alone?

No. The claims require a combination containing a covered carbonic anhydrase inhibitor and a specified beta-adrenergic antagonist. Dorzolamide alone is outside the combination limitations.

Does a dorzolamide/timolol product containing 2% and 0.5% fall within the patent?

Yes, those concentrations fall within the principal numerical ranges, and the carbonic anhydrase inhibitor concentration is greater than the beta-blocker concentration required by claim 15.

Can a generic avoid the claims by changing timolol maleate to another salt?

Not necessarily. The claims expressly include ophthalmologically acceptable salts. Changing the salt alone would not reliably avoid the patent scope.

Is a preservative-free dorzolamide/timolol product automatically outside the patent?

No. Preservative status is not a limitation of the broad claims. A preservative-free product would require a separate analysis of the active ingredients, concentrations, structural limitations, and any additional formulation claims.

References

U.S. Food and Drug Administration. (n.d.). Cosopt (dorzolamide hydrochloride and timolol maleate) ophthalmic solution prescribing information. Drugs@FDA.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. Orange Book.
United States Patent and Trademark Office. (2001). U.S. Patent No. 6,316,443, ophthalmic compositions containing carbonic anhydrase inhibitors and beta-adrenergic antagonists.
Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 355(j).
U.S. Food and Drug Administration. (2014). Abbreviated new drug application submissions: Refuse-to-receive standards. FDA guidance.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0509752	⤷ Start Trial	CA 2000 00002	Denmark	⤷ Start Trial
European Patent Office	0509752	⤷ Start Trial	C990041	Netherlands	⤷ Start Trial
European Patent Office	0509752	⤷ Start Trial	SPC/GB99/043	United Kingdom	⤷ Start Trial
European Patent Office	0509752	⤷ Start Trial	2000C/001	Belgium	⤷ Start Trial
European Patent Office	0509752	⤷ Start Trial	49/1999	Austria	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,316,443

Summary for Patent: 6,316,443