Generic SULFAMETHIZOLE INN equivalents, pharmaceutical patent expiration information and freedom to operate

Sponsor	Phase
Julio Ramirez	Early Phase 1
University of Louisville	Early Phase 1
James Graham Brown Cancer Center	Early Phase 1

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Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Forest Pharms	PROKLAR	sulfamethizole	TABLET;ORAL	080273-001	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Wyeth Ayerst	THIOSULFIL	sulfamethizole	TABLET;ORAL	008565-004	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Wyeth Ayerst	THIOSULFIL	sulfamethizole	TABLET;ORAL	008565-001	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Forest Pharms	MICROSUL	sulfamethizole	TABLET;ORAL	086012-001	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Exclusivity Expiration

Last updated: September 3, 2026

Sulfamethizole is a legacy sulfonamide antibacterial with no meaningful patent exclusivity, limited current clinical use, and a predominantly generic supply base. Its commercial profile is defined by low unit prices, small and fragmented demand, limited manufacturer concentration, and substitution by newer antibiotics. No reliable public source reports standalone global revenue for sulfamethizole, so financial analysis must rely on market structure, prescription demand, pricing, and regulatory status rather than company-level sales forecasts.

What is sulfamethizole and how is it used?

Sulfamethizole is an orally administered sulfonamide antibacterial. It inhibits bacterial dihydropteroate synthase and interferes with folate synthesis. Historical use centered on susceptible urinary tract infections and other bacterial infections, although resistance, adverse-event concerns, and availability of more effective agents have reduced its role.

Attribute	Sulfamethizole profile
Active ingredient	Sulfamethizole
Chemical class	Sulfonamide antibacterial
CAS number	723-46-6
Main historical dosage form	Oral tablet
Common historical strength	500 mg
Primary historical use	Susceptible bacterial infections, including urinary tract infections
Regulatory status	Legacy prescription antibacterial; current product availability varies by market
Patent status	No commercially relevant compound patent exclusivity
Market structure	Generic and fragmented
Biosimilar exposure	None
Main substitutes	Trimethoprim-sulfamethoxazole, nitrofurantoin, fosfomycin and other antibiotics, depending on infection and susceptibility

Sulfamethizole is distinct from sulfamethoxazole. The two drugs belong to the same broad sulfonamide class but have different molecular structures, labeling histories, commercial markets, and regulatory records.

What is the FDA regulatory status of sulfamethizole?

Sulfamethizole has a legacy FDA regulatory history, but its current U.S. commercial status is limited compared with widely used antibiotics. FDA labeling and listing records should be reviewed by product, manufacturer, dosage form, and marketing status because older products may be discontinued, transferred, or maintained in databases without active commercial distribution.

The FDA’s Drugs@FDA and Orange Book systems are the principal sources for determining whether a specific sulfamethizole product has an approved application, a reference listed drug designation, or therapeutic-equivalence information. The existence of an historical approval does not establish that the product remains actively marketed. FDA identifies drug products as discontinued or withdrawn from sale in separate regulatory records and publications.[1][2]

What dosage forms and formulations are marketed?

The commercially relevant form has historically been the oral tablet, particularly 500-milligram tablets. There is no established modern specialty formulation franchise around sulfamethizole.

The product lacks the commercial features that support formulation-based lifecycle management:

No widely marketed extended-release version
No major pediatric liquid franchise
No inhaled, injectable, ophthalmic, or depot formulation platform
No branded delivery system
No clinically differentiated combination product comparable to trimethoprim-sulfamethoxazole

Any current formulation value would arise from manufacturing reliability, regulatory status, supply continuity, or institutional purchasing rather than patent-protected differentiation.

When does sulfamethizole lose exclusivity?

Sulfamethizole lost practical exclusivity decades ago. The molecule is an old small-molecule antibacterial, and any original composition-of-matter patent protection has expired. There is no credible basis for treating sulfamethizole as a patent-protected growth product in the United States, Europe, or other mature pharmaceutical markets.

Exclusivity category	Sulfamethizole position
Compound patent	Expired
Core formulation patent	No commercially material active estate identified
Method-of-use exclusivity	No current material exclusivity identified
FDA five-year new chemical entity exclusivity	Not applicable to current market opportunity
Three-year clinical-investigation exclusivity	Not relevant to the established generic market
Pediatric exclusivity	No current commercial significance
Orphan exclusivity	Not applicable
Biosimilar exclusivity	Not applicable

What patents protect sulfamethizole?

No active patent estate appears to protect sulfamethizole as a commercially significant product. Historical patents covering the compound, synthesis, or early pharmaceutical use would have expired long ago. Any patent research should separate:

Historical compound patents.
Process patents for manufacturing or purification.
Formulation patents.
Use patents for a defined infection or patient population.
Patents covering a particular supplier’s intermediate or crystallization process.

A process patent could affect a specific manufacturer without creating market exclusivity for the active ingredient. In practice, sulfamethizole’s principal barriers are regulatory maintenance, quality compliance, raw-material sourcing, and low expected returns.

How many patents cover sulfamethizole?

The number of historical patent documents can be substantial because sulfamethizole has been referenced in compound, synthesis, formulation, and antibacterial patent filings. That count does not translate into current market protection.

The commercially relevant question is whether an unexpired patent blocks an abbreviated new drug application or generic launch. For sulfamethizole, the answer is generally no for the established oral-tablet market. Patent counts from Google Patents, Espacenet, WIPO Patentscope, or USPTO records should not be used without filtering for expiration, jurisdiction, claims, legal status, and claim scope.

What is the Orange Book status of sulfamethizole?

The Orange Book is relevant only where an approved U.S. reference product and associated patents or exclusivity are listed. For a legacy generic such as sulfamethizole, the practical Orange Book analysis is narrow:

Determine whether an active reference listed drug exists.
Determine whether any product-specific patents are listed.
Review therapeutic-equivalence codes for approved generic products.
Confirm whether the relevant product is currently marketed.
Distinguish an FDA-approved product from a product that is commercially available.

An Orange Book listing, if present for a legacy product, would not by itself indicate an attractive branded opportunity. It would indicate a regulatory reference point for generic substitution and approval.

Are there Paragraph IV challenges involving sulfamethizole?

Paragraph IV litigation is not a meaningful current market driver for sulfamethizole. A Paragraph IV certification challenges a listed patent in connection with an abbreviated new drug application. That pathway has commercial relevance when an active patent creates a launch barrier and the generic applicant has a meaningful first-to-file or litigation strategy.

Sulfamethizole’s old compound and conventional tablet profile provide little basis for a new, high-value Paragraph IV campaign. Any litigation would more likely involve:

A newly developed formulation
A novel fixed-dose combination
A new indication
A manufacturing process with enforceable claims
A supplier dispute involving regulatory files or raw materials

No established branded sulfamethizole franchise has generated the type of recurring patent litigation associated with major products such as inhaled therapies, oncology drugs, biologics, or complex injectables.

What is the competitive landscape for sulfamethizole?

Sulfamethizole competes in a mature antibacterial market where clinical selection is driven by pathogen susceptibility, resistance patterns, tolerability, guideline recommendations, and local formulary policy. Price is important for generic procurement but does not create strong demand when clinicians have more familiar alternatives.

How does sulfamethizole compare with competing antibiotics?

Drug or class	Competitive position versus sulfamethizole
Trimethoprim-sulfamethoxazole	Stronger modern clinical recognition and broader continuing use
Nitrofurantoin	Common alternative for uncomplicated urinary tract infection
Fosfomycin	Important alternative for selected urinary tract infections
Fluoroquinolones	Historically broader use, but constrained by safety and stewardship concerns
Penicillins and cephalosporins	Broad substitution set based on organism and infection site
Other sulfonamides	Limited and indication-specific competition

Sulfamethizole’s most direct commercial disadvantage is not a single competitor. It is substitution across several antibiotic classes, combined with antimicrobial stewardship policies that favor targeted and guideline-supported therapy.

Resistance is another structural constraint. Sulfonamide activity depends on organism susceptibility, and resistance can reduce empirical prescribing. Product labeling requires attention to microbiological testing and clinical context.[3]

What is the market size and revenue exposure for sulfamethizole?

No dependable public dataset provides standalone sulfamethizole revenue across global markets. Large pharmaceutical companies generally do not report the molecule separately, and generic manufacturers often aggregate low-volume products within broader portfolios.

The financial profile can be summarized as follows:

Financial factor	Expected impact
Unit price	Low
Volume growth	Flat to declining in mature markets
Gross-margin potential	Dependent on manufacturing scale and supply competition
Brand pricing power	Minimal
Reimbursement leverage	Limited
Switching costs	Low for therapeutically substitutable products
Commercial concentration	Fragmented among generic suppliers
Revenue visibility	Low at molecule level
Patent-related upside	Negligible
Supply disruption risk	Higher than demand-growth potential

Sulfamethizole can generate recurring revenue for a manufacturer with an efficient legacy portfolio, but it is unlikely to produce material growth without a supply shortage, a new indication, a differentiated formulation, or a market-specific regulatory opportunity.

What would drive a financial recovery?

A sustained increase in value would require an external market event rather than ordinary demand expansion. Potential drivers include:

Withdrawal of competing manufacturers
Shortage of a preferred alternative
Government procurement demand
Expanded use in a price-sensitive emerging market
A reformulated product with a meaningful clinical advantage
New evidence supporting a narrowly defined indication
Acquisition of a low-cost manufacturer with established registrations

These drivers would be difficult to forecast and would not create durable value unless supported by reliable supply and regulatory positioning.

What manufacturing and intellectual-property barriers exist?

Manufacturing barriers are more important than patent barriers. Sulfamethizole is a mature small molecule, but suppliers must meet current good manufacturing practice requirements, validate impurity controls, qualify active pharmaceutical ingredient sources, and maintain consistent tablet quality.

Potential operational risks include:

Limited qualified API suppliers
Dependence on a small number of manufacturing sites
Raw-material price volatility
Low production runs
Regulatory inspection findings
Product discontinuation caused by weak margins
Difficulty maintaining dossiers for a low-volume product

For a generic company, the key asset may be the approved regulatory file, supplier network, and manufacturing capability rather than intellectual property. A company with an established product registration can have a modest defensive advantage even when the underlying molecule is unpatented.

What geographic markets offer commercial opportunity?

Mature markets such as the United States, Western Europe, Canada, Japan, and Australia generally offer limited growth potential because of generic competition, antimicrobial stewardship, and substitution by better-established agents.

Emerging markets may have greater unit demand, but pricing is often lower and regulatory, distribution, quality, and payment risks are higher. Market entry depends on country-specific registration, local pharmacopoeial requirements, procurement channels, and whether sulfamethizole remains included in treatment protocols.

Region	Commercial outlook
United States	Legacy generic opportunity with limited growth
European Union	Low-value market with country-specific availability
Latin America	Possible demand in selected public and private channels
Asia-Pacific	Manufacturing and procurement relevance; highly variable demand
Middle East and Africa	Potential institutional demand, subject to registration and supply economics

What generic launch scenarios exist for sulfamethizole?

A conventional generic launch would face few patent barriers but also limited commercial upside. The principal scenarios are:

Low-volume continuation

An existing manufacturer maintains supply for institutional, specialty, or legacy prescribing channels. This is the most plausible scenario where demand remains stable but small.

Portfolio rationalization

A manufacturer exits because the product does not justify ongoing regulatory and manufacturing costs. This could reduce supplier competition and create temporary shortages.

Opportunistic re-entry

A generic company reintroduces the product after competitor withdrawals or procurement demand. The opportunity would depend on an available reference product, an approvable regulatory pathway, and reliable API supply.

Reformulation or combination strategy

A company develops a new formulation or combination product. This could create regulatory differentiation, but it would require clinical, manufacturing, and commercial justification that sulfamethizole has not recently demonstrated.

What licensing deals and transactions involve sulfamethizole?

Sulfamethizole is not associated with a visible current licensing market comparable to patented antibiotics, specialty anti-infectives, or branded combination products. Any transaction is more likely to involve:

Transfer of an approved generic application
Acquisition of a legacy product portfolio
Contract manufacturing
Regional distribution rights
API supply arrangements
Government or institutional procurement

The absence of a known high-value licensing franchise reflects the molecule’s generic status, low pricing, and limited product differentiation.

How strong is the sulfamethizole patent estate?

The patent estate is weak from a commercial-exclusivity perspective. Its strength is best assessed across four dimensions:

Dimension	Assessment
Composition-of-matter protection	Expired
Formulation protection	Limited or immaterial for conventional tablets
Method-of-use protection	No current material barrier identified
Manufacturing protection	Potentially relevant to individual processes, but not market-wide
Regulatory exclusivity	No current meaningful exclusivity
Litigation deterrence	Low
Generic entry barrier	Low

Sulfamethizole can still have operational value, but its patent estate does not support premium pricing or a protected market.

Key Takeaways

Sulfamethizole is a legacy generic sulfonamide antibacterial with limited current commercial relevance.
Practical compound and product exclusivity expired decades ago.
The principal dosage form is the conventional oral tablet, with little evidence of a differentiated formulation franchise.
Orange Book analysis is product-specific and should distinguish historical approval from active marketing.
Paragraph IV litigation and biosimilar competition are not meaningful current risks.
Revenue is not publicly reported at the molecule level and is likely low, fragmented, and difficult to forecast.
Market demand is constrained by antimicrobial resistance, stewardship policies, and substitution by trimethoprim-sulfamethoxazole, nitrofurantoin, fosfomycin, beta-lactams, and other antibiotics.
Manufacturing continuity, API sourcing, and regulatory-file maintenance matter more than patent protection.
The most credible commercial upside would come from competitor withdrawal, supply shortages, public procurement, or a differentiated reformulation.

FAQs

Is sulfamethizole still available in the United States?

Availability depends on the specific manufacturer, product registration, and marketing status. Historical FDA approval or database presence does not establish active commercial distribution.

Is sulfamethizole included in modern urinary tract infection guidelines?

Use depends on local susceptibility patterns, patient characteristics, infection type, and applicable treatment guidelines. It is generally less prominent than nitrofurantoin, trimethoprim-sulfamethoxazole, and fosfomycin for uncomplicated urinary tract infections.

Can a company obtain new patents on sulfamethizole?

A new patent could potentially cover a novel formulation, combination, manufacturing process, or defined method of use if statutory patent requirements are met. A patent on the old molecule itself would not be available.

Does sulfamethizole qualify for 180-day generic exclusivity?

A generic applicant could qualify for statutory exclusivity only under the applicable FDA rules and filing circumstances. The molecule’s old status does not automatically confer 180-day exclusivity on a new applicant.

Is sulfamethizole a biosimilar opportunity?

No. Sulfamethizole is a chemically synthesized small molecule, so it is regulated through generic-drug pathways rather than the biosimilar pathway for biologics.

References

U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs. https://www.accessdata.fda.gov/scripts/cder/daf/
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book-overview
U.S. National Library of Medicine. (n.d.). DailyMed: Sulfamethizole drug labeling. https://dailymed.nlm.nih.gov/dailymed/
U.S. Food and Drug Administration. (2016). Drug products withdrawn or removed from the market for reasons of safety or effectiveness. https://www.fda.gov/drugs/drug-safety-and-availability
World Health Organization. (2023). The WHO AWaRe antibiotic book: Infographics and practical guidance for health-care professionals. https://www.who.int/publications/i/item/9789240062382

US Patents:	0
Tradenames:	3
Applicants:	2
NDAs:	3
Drug Master File Entries:	4
Raw Ingredient (Bulk) Api Vendors:	94
Clinical Trials:	1
DailyMed Link:	SULFAMETHIZOLE at DailyMed

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