U.S. Drug Patent RE30633: Claim Scope, Torsemide Coverage, Expiration and Patent Landscape

U.S. Patent RE30,633 is an expired U.S. reissue patent covering substituted 3-aminopyridine compounds, including torsemide, also known as torasemide. Its claims extend across a Markush genus of aminopyridines, selected urea- and carbamoyl-sulfonamide derivatives, pyridine N-oxides, pharmaceutically acceptable salts, and pharmaceutical compositions. Claim 11 specifically recites torsemide.

The patent no longer creates an enforceable U.S. composition-of-matter barrier. Its underlying pre-URAA patent term ended in 2001, and no biosimilar pathway is relevant because torsemide is a small-molecule drug. The commercial risk today concerns generic competition, formulation differentiation, manufacturing controls and regulatory exclusivities rather than RE30,633 infringement.

What drug does U.S. Patent RE30633 cover?

RE30,633 covers a chemical class of substituted 3-sulfonamido-4-arylaminopyridines. The most commercially important compound is torsemide:

Torsemide chemical identity

1-Isopropyl-3-[(4-m-toluidino-3-pyridyl)sulfonyl]urea
Also called torasemide
Loop diuretic
U.S. brand: Demadex
Therapeutic uses: edema associated with congestive heart failure, renal disease and hepatic disease; hypertension in approved labeling

The patent’s expressly recited torsemide species is:

3-Isopropylcarbamylsulfonamido-4-(3'-methyl)phenylaminopyridine

That language corresponds to an isopropyl-substituted sulfonylurea attached to a 3-methylphenylaminopyridine core.

What patents protect torsemide?

The principal historical U.S. composition patent was the patent underlying RE30,633. The reissue claims cover torsemide as an individual compound and as part of a broader chemical genus.

Item	Description
Patent	U.S. Patent RE30,633
Patent type	Reissue patent
Core technology	Substituted aminopyridine sulfonylurea and sulfonamide compounds
Important species	Torsemide
Relevant claim	Claim 11
Pharmaceutical use	Diuretic compositions and treatment
Original term	Pre-URAA 17-year term
U.S. term status	Expired
Commercial consequence	No current blocking patent right from RE30,633

The reissue did not create a new patent term. Under U.S. reissue law, the reissue patent carries the remaining term of the original patent. The underlying patent term ended in 2001 based on the original grant date and the pre-URAA 17-year patent-term regime. Patent term adjustment and patent term extension rules did not produce a current enforceable term for this legacy patent. [1]

What is the scope of claim 1 of RE30633?

Claim 1 is a broad Markush claim directed to a substituted aminopyridine scaffold represented by the formula in the patent. Because the chemical structure image is not reproduced in the claim text supplied, the scope is best analyzed through the defined substituents.

The claim controls several structural positions:

Variable	Permitted substituents
X	Amino or C1-C4 alkylamino
R1	Carbamoylsulfonamide-related groups, including alkyl, allyl, cyclohexyl and phenyl variants; additional carbonyl forms apply under specified provisos
R2	Hydrogen or C1-C4 alkyl
Z	C1-C4 alkyl, methylfuryl, pyridyl, phenyl and substituted phenyl groups
A	Oxygen or sulfur
R3	C1-C4 alkyl, allyl, cyclohexyl, phenyl or chlorophenyl
R4	Phenyl or chlorophenyl
Salt forms	Pharmaceutically acceptable base-addition and acid-addition salts
Oxidation state	Pyridine N-oxide forms are included

The claim has a layered structure. It first establishes a broad genus. The provisos then narrow the permitted combinations depending on whether X is amino or alkylamino and whether Z is phenyl-based or non-phenyl-based.

Why the provisos matter

The provisos restrict combinations rather than merely defining isolated substituents.

When X is amino, the full set of listed meanings remains available.
When X is alkylamino, Z is limited to an alkyl or specified phenyl group, and R1 may include an aldehyde- or ketone-derived carbonyl group.
When X is amino and Z is not phenyl, R1 may include hydrogen or the separately defined carbonyl group.

These limitations reduce the number of covered combinations and would be relevant to both infringement analysis and validity analysis. A compound cannot be assessed by matching one substituent at a time. The complete combination, including the applicable proviso, must fall within the claim.

How does claim 9 differ from claim 1?

Claim 9 is an amended independent compound claim with a different formula and a narrower variable set. It defines:

R as hydrogen or C1-C4 alkyl;
R2 as hydrogen or C1-C4 alkyl;
R3 as C1-C4 alkyl, allyl, cyclohexyl, phenyl or chlorophenyl;
A as oxygen or sulfur;
Z as alkyl, methylfuryl, pyridyl, phenyl or substituted phenyl.

Claim 9 also contains a key limitation: when R is a C1-C4 alkyl group, Z may only be an alkyl or permitted phenyl group.

Compared with claim 1, claim 9 is narrower in several respects:

It does not preserve every alternative apparent in claim 1.
It uses a simplified variable structure.
It expressly limits the relationship between R and Z.
It does not reproduce all of claim 1’s R1 and R4 alternatives.

Claim 9 is important because it provides the structural platform for claim 10 and supports the amended claim architecture reflected in the reissue text.

Which claims specifically cover torsemide?

Claim 11 expressly recites torsemide:

3-Isopropylcarbamylsulfonamido-4-(3'-methyl)phenylaminopyridine.

This is the strongest claim for identifying the patent’s torsemide coverage. It is a product claim directed to the individual chemical compound rather than only to a broad genus.

The claim set also includes related species:

Claim	Subject matter
Claim 1	Broad substituted aminopyridine genus
Claims 2-7	Specific substituted aminopyridine compounds, including N-oxides and aryl derivatives
Claim 8	Pharmaceutical composition language as amended
Claim 9	Independent compound genus with revised substituent definitions
Claim 10	Subgenus defined by R, R3, A and Z
Claim 11	Torsemide species
Claim 12	Diuretic composition containing the compound identified in claim 3

The supplied text contains apparent editorial artifacts, including bracketed deletions and additions and a reference in claim 8 to "the compound of claim 9." Those artifacts reflect reissue claim amendments. The issued patent text, rather than a transcription, controls the legal construction.

What formulations are protected by RE30633?

RE30,633 contains composition coverage, but it does not appear from the supplied claims to claim a sophisticated delivery system, release profile, particle-size distribution or specific excipient matrix.

The composition claims generally require:

A diuretic-effective amount of a covered compound; and
A pharmaceutical carrier.

That language is broad but functionally limited. It can reach conventional oral dosage forms containing a covered compound, such as tablets, capsules or other pharmaceutical presentations, provided the composition satisfies the claim elements.

It does not necessarily cover every torsemide product independently. A formulation claim typically requires more specific elements, such as:

A defined excipient combination;
A dissolution profile;
A particle-size range;
A solid-state form;
A controlled-release mechanism;
A manufacturing process; or
A specific dosage regimen.

RE30,633’s composition language is therefore materially weaker than a modern formulation patent for present-day product differentiation. Its practical importance was historically tied to the underlying active compound, not to a technically narrow delivery platform.

Does RE30633 cover torsemide salts and N-oxides?

Yes, the claim language expressly includes pharmaceutically acceptable salts and pyridine N-oxide forms.

Salt coverage

The patent covers pharmaceutically acceptable acid-addition and base-addition salts where the claimed compound contains the relevant ionizable functionality. The salt language broadens the claim beyond a single neutral molecular form.

For a modern freedom-to-operate analysis, the salt language would be evaluated together with:

Whether the salt is genuinely a claimed pharmaceutical salt;
Whether the underlying compound satisfies the structural limitations;
Whether the salt was known or enabled in the patent;
Whether later patents separately claim a crystalline or amorphous form.

N-oxide coverage

The patent expressly recites pyridine N-oxide versions of the claimed compounds. The N-oxide species listed in the earlier claims are chemically distinct from torsemide itself and should not automatically be treated as torsemide claims.

The N-oxide provisions were significant for the original invention because they expanded the chemical estate. They have limited current commercial relevance unless a marketed product uses an N-oxide form.

When did RE30633 lose exclusivity?

RE30,633 lost U.S. patent exclusivity when the underlying patent term expired in 2001. Reissue status did not restart the term.

Exclusivity element	Status
Composition-of-matter patent	Expired
Reissue patent	Expired with underlying patent term
Patent term extension	No current extension affecting market entry
Patent term adjustment	Not a source of present exclusivity
Regulatory exclusivity	Expired
Generic entry	Legally available subject to FDA approval
Current patent barrier	None from RE30,633

The FDA approval of Demadex occurred in the early 1990s, and the historical exclusivity period has long ended. [2]

What is the Orange Book status of torsemide?

The Orange Book is relevant because torsemide is a small-molecule prescription drug approved through an NDA and subsequently subject to ANDA competition. The Orange Book does not provide continuing exclusivity from RE30,633 because that patent has expired. [3]

The commercial Orange Book analysis should distinguish between:

The original NDA for Demadex;
Expired patents that were historically listed;
Current patents, if any, covering a specific NDA formulation or use;
ANDA certifications made by generic applicants; and
Whether a listed patent remains enforceable on the relevant product.

For ordinary immediate-release torsemide tablets, the principal historical composition patent is no longer an entry barrier. A current applicant’s risk would arise from a separate unexpired patent listed against a specific reference product, not from RE30,633.

Were there Paragraph IV challenges to torsemide?

Torsemide has been subject to generic competition, and ANDA applicants could challenge expired or then-listed patents through Paragraph IV certifications. Once the relevant patent term expired, a Paragraph IV certification no longer created a meaningful patent-infringement exposure for RE30,633.

A Paragraph IV certification is a regulatory statement that a listed patent is invalid, unenforceable or not infringed. It can trigger patent litigation if made before patent expiry, but it does not preserve the patent owner’s rights after expiration.

For RE30,633, the current assessment is:

Historical Paragraph IV relevance: possible during the pre-expiration generic filing period;
Current Paragraph IV relevance: none for an expired patent;
Current generic risk: regulatory approval, manufacturing and product-specific patent issues;
Current litigation exposure under RE30,633: none.

The patent record supplied does not identify a specific ANDA applicant, litigation docket or settlement agreement. No company should be characterized as a historical challenger without confirmation from FDA ANDA records or federal court filings.

Which companies challenged torsemide exclusivity?

The major commercial competition came from generic manufacturers after the Demadex patent and exclusivity period ended. Public FDA records identify multiple approved torsemide products over time, but the supplied patent record does not establish a complete historical list of Paragraph IV filers or settlement counterparties.

The relevant competitive categories are:

Competitor type	Role
Original NDA holder	Commercialized Demadex
Generic tablet manufacturers	Entered after patent and regulatory barriers ended
Contract manufacturers	Produced active pharmaceutical ingredient or finished dosage forms
Specialty suppliers	Competed on supply, wholesaling and hospital contracts
Formulation developers	Could differentiate through dosage form or release characteristics

A patent landscape should not equate an approved generic manufacturer with a Paragraph IV challenger. Approval may follow a Paragraph III certification, patent expiration or a non-infringement position that never resulted in reported litigation.

What patent litigation affects RE30633?

RE30,633 is an expired legacy patent. It does not present a current litigation threat for ordinary torsemide manufacture or sale.

The likely historical legal issues included:

Whether generic compounds fell within the Markush genus;
Whether the expressly claimed torsemide species was valid;
Whether the reissue claims complied with reissue limitations;
Whether the amended claims enlarged the original claim scope;
Whether the composition claims were sufficiently enabled;
Whether particular salts or N-oxides were within the written description; and
Whether generic products were covered during the remaining term.

The reissue format creates a particular legal issue: reissue cannot be used to enlarge claim scope after two years from the original patent grant. The added or amended claims would therefore have been exposed to a statutory recapture and enlargement analysis under 35 U.S.C. § 251, depending on the original patent’s dates and prosecution history. [4]

That historical validity question has no present market consequence because the patent has expired.

How strong is the RE30633 patent estate?

Historical strength

The estate was commercially strong during its effective term because it combined:

A broad chemical genus;
Specific compound claims;
Torsemide-specific coverage;
Salt coverage;
N-oxide coverage; and
Pharmaceutical composition claims.

The genus claim could have reached structurally varied competitors, while claim 11 provided a direct species claim against torsemide itself.

Current strength

Current enforceability is zero because the patent term has ended. The estate has no remaining blocking value for U.S. torsemide entry.

Strength factor	Assessment
Direct torsemide claim	Historically strong; expired
Markush genus	Broad but subject to construction and validity limits
Salt coverage	Broad historical protection
N-oxide coverage	Technically broad, commercially limited
Formulation protection	Limited based on supplied claim text
Method-of-use protection	No detailed modern method claim apparent
Manufacturing protection	No separate process claim apparent in supplied text
Current enforceability	None

Are there biosimilar risks for torsemide?

No. Torsemide is a chemically synthesized small molecule, not a biologic subject to the biosimilar pathway under the Public Health Service Act.

Competitive products use the ANDA pathway under section 505(j) of the Federal Food, Drug, and Cosmetic Act. The relevant regulatory issues include:

Pharmaceutical equivalence;
Bioequivalence;
Strength and dosage form;
Labeling;
Manufacturing controls;
Drug Master File support for active ingredient supply; and
Any unexpired patents listed for the applicable reference product.

The absence of biosimilar risk does not eliminate manufacturing or regulatory risk. It means that the principal approval route is generic substitution through ANDAs rather than biosimilar interchangeability.

What manufacturing and IP barriers remain?

RE30,633 does not create a current manufacturing barrier. Remaining barriers are commercial and regulatory:

Consistent synthesis of the aminopyridine intermediate;
Control of regioisomeric impurities;
Control of residual solvents and genotoxic impurities;
Reproducible sulfonylurea formation;
API polymorph and particle-size control;
Stability in the final dosage form;
FDA cGMP compliance;
ANDA bioequivalence;
Reliable API sourcing; and
State substitution and contracting requirements.

A later patent could still create risk if it claims a specific torsemide polymorph, formulation, manufacturing process or method of treatment. Such a patent would be separate from RE30,633 and must be assessed independently.

What is the geographic coverage of RE30633?

RE30,633 is a U.S. patent. Its rights were limited to the United States. Foreign counterparts, if granted, required separate country-by-country validity and term analysis.

The international landscape for torsemide historically included European and other national filings. Those rights would have had independent:

Priority dates;
Grant dates;
Patent-term calculations;
Opposition or revocation histories;
Supplementary protection certificate issues; and
National claim scopes.

Expiration of the U.S. reissue did not automatically determine the status of foreign family members. For current U.S. entry, however, foreign rights have no direct blocking effect.

Key Takeaways

RE30,633 covers substituted aminopyridine sulfonamide and sulfonylurea compounds.
Claim 11 specifically covers torsemide.
Claim 1 is a broad Markush genus with multiple structural provisos.
Claim 9 is a revised independent compound claim with narrower variable relationships.
The patent includes salt, N-oxide and pharmaceutical composition coverage.
The underlying patent term ended in 2001.
RE30,633 is expired and cannot block current U.S. torsemide entry.
Torsemide is subject to the generic ANDA pathway, not the biosimilar pathway.
Current risk must be assessed against later formulation, polymorph, manufacturing or method-of-use patents, not RE30,633.
The principal present barriers are FDA approval, cGMP manufacturing, API supply and commercial contracting.

FAQs About U.S. Patent RE30633 and Torsemide

Is torsemide still patented in the United States?

The RE30,633 patent covering torsemide is expired. Any current patent risk would have to arise from a later patent directed to a particular formulation, solid form, manufacturing process or use.

Does RE30633 cover torsemide tablets?

The composition claims can reach pharmaceutical compositions containing a covered compound and a carrier. They do not, based on the supplied text, require a specific tablet technology or excipient system.

Can a company manufacture generic torsemide in the United States?

Yes, subject to FDA ANDA approval, cGMP compliance, bioequivalence and review of any separate unexpired patents applicable to the proposed product.

Does the patent cover torsemide hydrochloride or other salts?

The claim language includes pharmaceutically acceptable acid-addition and base-addition salts. The precise scope depends on the chemical structure and whether the salt satisfies the claim and enablement requirements.

Is a Paragraph IV certification still needed for RE30633?

No current Paragraph IV certification is needed to challenge an expired patent. The applicant must still evaluate any other patent listed for the applicable reference product and certify as required under FDA regulations.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	16836/74	Apr 17, 1974

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	208768	⤷ Start Trial
Argentina	208769	⤷ Start Trial
Argentina	208770	⤷ Start Trial
Argentina	211097	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: RE30633

Summary for Patent: RE30633