US Patent 5,962,461: Claim Scope, Expiration, and Pharmaceutical Formulation Patent Landscape

US Patent 5,962,461 covers ethanol-free, transparent oral liquid compositions designed to mask the bitterness of selected drugs. The claim set requires a narrow excipient architecture: polyvinylpyrrolidone, a C3-C6 polyol, ammonium glycyrrhizinate, water, flavorants, and a bitter-tasting active ingredient. The patent expired in 2017, so its claims no longer create an enforceable exclusionary right. Its technical disclosure remains relevant for formulation design, freedom-to-operate analysis, and prior-art review. [1]

What does US Patent 5,962,461 protect?

The patent protects compositions rather than a treatment method, manufacturing process, dosage regimen, or pharmaceutical kit. Its central formulation concept combines:

Required element	Claimed range or limitation
Pharmaceutical active	Bitter-tasting drug
Active categories in generic claims	Vitamin preparation or minerals
Named species claims	Trimethoprim and guaifenesin
Primary vehicle	Aqueous medium free of ethanol
Polyvinylpyrrolidone	About 5-30 wt%; narrower claims use 7-15 wt%
C3-C6 polyol	About 35-55 wt%; narrower claims use 45-55 wt%
Ammonium glycyrrhizinate	About 0.01-0.5 wt%
Flavorants	One or more
Physical property	Transparent liquid
Organoleptic property	Pleasant taste on oral administration
Active concentration	Generally 0.5-5 wt%; narrower claims use 1-3 wt%
Polyol combination	C3 polyol plus C6 polyol in selected claims
C3:C6 polyol ratio	About 1:4 to 3:5 in claims 8, 19, and 28

The composition must satisfy the full combination of limitations. A liquid containing guaifenesin, for example, would not fall within claims 22-30 unless it also contains the specified polyvinylpyrrolidone, polyol, ammonium glycyrrhizinate, aqueous ethanol-free medium, flavorant, transparency, and claimed concentration or ratio limitations.

How are the claims organized?

The claims form four overlapping groups.

Claims 1-5: broad generic formulation claims

Claim 1 is the principal generic claim. It requires a bitter-tasting drug selected from a vitamin preparation or minerals and an aqueous medium containing:

5-30 wt% polyvinylpyrrolidone;
35-55 wt% C3-C6 polyol;
0.01-0.5 wt% ammonium glycyrrhizinate; and
flavorants.

Claims 2-5 narrow claim 1 by specifying the polyvinylpyrrolidone range, a mixed-polyol system, the ammonium glycyrrhizinate-to-drug ratio, and the drug concentration.

The use of "consisting essentially of" limits the excipient system to listed components plus ingredients that do not materially affect the basic and novel characteristics of the composition. The phrase is broader than "consisting of," but narrower than "comprising." Preservatives, buffers, coloring agents, sweeteners, stabilizers, or additional solvents could create an infringement issue if they materially alter the claimed taste-masking or transparent-liquid system.

Claims 6-12: narrower generic formulation platform

Claims 6-12 recite a more concentrated formulation platform:

7-15 wt% polyvinylpyrrolidone;
45-55 wt% C3-C6 polyol;
0.01-0.5 wt% ammonium glycyrrhizinate;
ammonium glycyrrhizinate-to-drug ratio of about 1:50 to 1:10;
drug concentration of 0.5-5 wt%, or 1-3 wt% in claim 10.

Claims 7 and 8 require or further define a C3/C6 polyol mixture. Claim 9 limits non-C6 polyol content to less than approximately 5 wt%, creating a formulation centered substantially on the C6 polyol component.

Claims 13-21: trimethoprim compositions

Claims 13-21 apply the formulation platform specifically to trimethoprim. The claims require the same core excipient system and add trimethoprim as the active ingredient.

The important commercial limitation is the combination of:

0.5-5 wt% trimethoprim;
7-15 wt% polyvinylpyrrolidone;
45-55 wt% C3-C6 polyol;
0.01-0.5 wt% ammonium glycyrrhizinate; and
ammonium glycyrrhizinate-to-trimethoprim ratio of approximately 1:50 to 1:10.

Claims 17-21 repeat the narrower concentration and mixed-polyol architecture.

Claims 22-30: guaifenesin compositions

Claims 22-30 apply the formulation to guaifenesin. The claimed guaifenesin concentration is 0.5-5 wt%, with claim 30 narrowing the range to approximately 1-3 wt%.

This group is commercially relevant to oral cough and cold liquids. The patent does not cover every guaifenesin syrup. It covers guaifenesin liquids that meet the specified excipient, concentration, transparency, ethanol-free, and taste-related limitations.

What are the strongest and weakest claim limitations?

The patent’s strongest practical limitation is the required excipient combination. A competitor would need to satisfy multiple quantitative ranges simultaneously. The most important limitations are:

Ethanol-free aqueous medium.
Polyvinylpyrrolidone at 7-15 wt% in the narrower claims.
C3-C6 polyol at 45-55 wt%.
Ammonium glycyrrhizinate at 0.01-0.5 wt%.
Specific ammonium glycyrrhizinate-to-active ratio.
Transparent liquid presentation.
Pleasant oral taste.
Specified drug identity or drug category.

The weakest limitations for enforcement are likely the functional terms "transparent" and "pleasant taste." Their application depends on objective testing, sample preparation, lighting, sensory methodology, and the relevant skilled person’s understanding. Functional limitations can be enforceable, but they may create disputes over testing protocols and claim construction.

The numerical ranges also create potential noninfringement positions. A composition containing 6 wt% polyvinylpyrrolidone may fall outside claims requiring 7-15 wt%, even if it is close to the claimed formulation. The doctrine of equivalents could become relevant, but the prosecution history and any disclosed criticality of the ranges would control.

What formulations are protected by US 5,962,461?

The following formulation would fall within the technical center of the narrower claims if all other limitations are satisfied:

Component	Example concentration
Trimethoprim or guaifenesin	1-3 wt%
Polyvinylpyrrolidone	7-15 wt%
C3 polyol	Part of a 45-55 wt% total polyol system
C6 polyol	Balance of the polyol system
Ammonium glycyrrhizinate	0.01-0.5 wt%
Water	Balance
Flavorant	Present
Ethanol	Absent
Finished product	Transparent and palatable

The disclosure is directed to taste masking and solubilization or dispersion. Polyvinylpyrrolidone likely contributes to drug solubilization and mouthfeel. Polyols contribute sweetness, viscosity, and solvent properties. Ammonium glycyrrhizinate functions as a flavor-modifying or taste-masking agent.

A composition may avoid the literal scope by using a different polymer, replacing ammonium glycyrrhizinate with another taste-masking agent, using a nonaqueous or ethanol-containing system, changing the polyol profile, or selecting a drug outside the expressly claimed categories and species. Each design-around requires a complete limitation-by-limitation analysis.

When did US Patent 5,962,461 lose exclusivity?

US Patent 5,962,461 issued on October 5, 1999. Its ordinary US patent term ran from the applicable nonprovisional filing date and ended in 2017. The patent is expired and no longer blocks commercial manufacture, sale, or use under 35 U.S.C. §§ 271 and 283. [1, 2]

Event	Date or status
US patent application	1990s filing
Patent issued	October 5, 1999
Patent number	US 5,962,461
Patent term	Ended in 2017
Current enforceability	Expired
Patent-term extension	No relevant extension identified
Post-expiration use	Claims remain prior art and technical disclosure

The expiration analysis should be separated from regulatory exclusivity. Patent expiration does not eliminate FDA requirements for approval, labeling, manufacturing controls, or product-specific safety and efficacy data.

What is the Orange Book status of US Patent 5,962,461?

US Patent 5,962,461 does not operate as an active Orange Book barrier based on the claim subject matter and its expired status. The Orange Book lists patents submitted for approved prescription drug products, including drug substance, drug product, and method-of-use patents. A formulation patent covering a legacy liquid composition may be listed only if it was submitted for a qualifying approved product and met FDA listing requirements. [3]

The patent is not a biologic patent and has no biosimilar relevance. Trimethoprim and guaifenesin are small-molecule actives. Any ANDA applicant would analyze applicable Orange Book listings for the particular reference listed drug, not merely the historical existence of US Patent 5,962,461.

Are there Paragraph IV challenges or generic-launch risks?

A Paragraph IV certification is relevant only when an applicant files an ANDA against an approved reference listed drug with a listed patent. Because US Patent 5,962,461 expired in 2017, it does not create a current 30-month-stay or Paragraph IV barrier.

Generic-launch risk therefore depends on other rights:

active-ingredient patents, if any;
formulation patents filed after US 5,962,461;
method-of-use patents;
pediatric exclusivity or other statutory exclusivity;
product-specific Orange Book listings;
trademarks and trade dress;
manufacturing know-how and supplier controls.

For guaifenesin products, FDA’s OTC monograph framework may be more important than an ANDA challenge, depending on the product, indication, dosage form, and applicable regulatory pathway. [4] Trimethoprim products may require an approved application and can present different prescription-drug regulatory issues.

What patent litigation and settlement agreements affect the patent?

The patent’s expiration removes the principal economic basis for an injunction or damages claim based on future conduct. No current litigation or settlement position can preserve an expired patent’s exclusionary term. Historical litigation, if any, would concern conduct before expiration and would require review of PACER, district-court dockets, Federal Circuit decisions, and the patent’s prosecution history.

No active settlement-based launch restriction should be inferred from the patent itself. A commercial agreement, supply contract, trademark settlement, or confidentiality obligation could survive patent expiration, but those rights would arise from the agreement rather than from claims 1-30.

How does this patent compare with competing formulation patents?

US 5,962,461 is a composition patent with a narrow excipient fingerprint. It differs from other pharmaceutical formulation patents in several respects.

Patent category	Primary protection	Relevance to this patent
Drug-substance patent	Active ingredient or chemical entity	Separate from 5,962,461
Salt or polymorph patent	Solid-state or chemical form	Usually not implicated by this liquid formulation patent
Formulation patent	Excipients, concentration, dosage form	Closest category
Method-of-use patent	Treatment indication or patient group	Not claimed here
Manufacturing patent	Mixing, sterilization, filling, processing	Not claimed here
Trademark rights	Product name and branding	Independent of patent claims
Trade-secret rights	Taste-masking process or manufacturing parameters	May remain relevant after patent expiration

The patent’s technical value is concentrated in the interaction among polyvinylpyrrolidone, polyol, ammonium glycyrrhizinate, and flavorant. A later patent could still block a particular commercial product through a different formulation, process, or use claim.

What geographic coverage does US Patent 5,962,461 provide?

The patent provides US rights only. It does not establish protection in Canada, Europe, Japan, China, or other jurisdictions. Foreign counterparts would require separate patent-family analysis. Since the US patent expired in 2017, any foreign family member would need an independent review of filing dates, national-phase status, term adjustments, and expiration.

A company commercializing an equivalent liquid in another country should not assume that the US expiration ended foreign rights. Conversely, foreign patents cannot restore an expired US claim.

How strong is the patent estate for commercial products?

The estate is no longer commercially strong as an exclusionary right because the US patent is expired. Its historical claim quality was moderate to strong against products that copied the complete formulation architecture, especially the narrower trimethoprim and guaifenesin claims.

Factor	Assessment
Claim breadth	Moderate; broad concept narrowed by many required ingredients
Quantitative specificity	High
Design-around potential	Moderate to high
Litigation leverage today	None from the expired US claims
Orange Book impact	No current blocking effect identified
Biosimilar exposure	None
Generic exposure	High after expiration, subject to other patents
Manufacturing barrier	Low from the patent alone
Know-how value	Potentially meaningful if process details are proprietary

Key Takeaways

US Patent 5,962,461 covers ethanol-free, transparent oral liquids containing a bitter drug, polyvinylpyrrolidone, C3-C6 polyol, ammonium glycyrrhizinate, and flavorants.
Claims 13-21 target trimethoprim; claims 22-30 target guaifenesin.
The principal commercial limitations are the excipient combination, concentration ranges, ammonium glycyrrhizinate-to-drug ratio, transparency, and palatability.
The patent expired in 2017 and does not create a current US patent barrier.
There is no biosimilar issue because the claimed products contain small-molecule actives.
Paragraph IV risk from this patent is no longer material, although other Orange Book patents may affect a particular reference product.
The patent remains relevant as prior art and as a formulation design reference.
Claims 15 and 29, as reproduced in the question, contain apparent dependency or drafting inconsistencies. The issued patent and prosecution file control over the text supplied here.

FAQs About US Patent 5,962,461

Does US Patent 5,962,461 cover all liquid guaifenesin products?

No. It covers only guaifenesin liquids satisfying the specified excipient, concentration, ethanol-free, transparency, flavor, and ammonium glycyrrhizinate limitations.

Can a company use ammonium glycyrrhizinate in a liquid drug product after the patent expired?

Yes. The expired patent does not prevent use of the claimed combination. Other patents, regulatory requirements, and third-party rights must be assessed separately.

Is trimethoprim formulation protection still active under this patent?

No. The US claims expired in 2017.

Does the patent cover a manufacturing process for the liquid composition?

No. The claims provided are composition claims. They do not expressly claim mixing order, heating, sterilization, filling, or packaging operations.

Can the expired patent be cited against a later patent application?

Yes. Its disclosure and claims may be prior art under applicable novelty and obviousness standards, subject to the later application’s filing date, effective prior-art date, and statutory exceptions.

References

United States Patent and Trademark Office. (1999). US Patent No. 5,962,461. https://patents.google.com/patent/US5962461
United States Code. (2024). 35 U.S.C. §§ 154, 271, and 283. https://uscode.house.gov
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book
U.S. Food and Drug Administration. (2024). Over-the-counter monograph drugs. https://www.fda.gov/drugs/over-counter-otc-nonprescription-drugs%timeout

PCT Information
PCT Filed	August 07, 1997	PCT Application Number:	PCT/US97/14018
PCT Publication Date:	February 12, 1998	PCT Publication Number:	WO98/05312

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	236624	⤷ Start Trial
Australia	3913297	⤷ Start Trial
Australia	727175	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,962,461

Summary for Patent: 5,962,461