Sulfonamide Antibacterial Drug Class List

Drugs in Drug Class: Sulfonamide Antibacterial

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Thepharmanetwork Llc	THERMAZENE	silver sulfadiazine	CREAM;TOPICAL	018810-001	Dec 23, 1985	AB	RX	No	No
Chartwell Molecular	SULFADIAZINE	sulfadiazine	TABLET;ORAL	080084-001	Approved Prior to Jan 1, 1982		DISCN	No	No
Epic Pharma Llc	SULFADIAZINE	sulfadiazine	TABLET;ORAL	040091-001	Jul 29, 1994		RX	No	Yes

Last updated: July 6, 2026

Market dynamics and patent landscape for sulfonamide antibacterials: exclusivity, Orange Book status, and generic entry risk

Sulfonamide antibacterials remain a large, mature segment dominated by off-patent generics, limited incremental innovation, and a patent landscape that is more often about formulation, polymorphs, manufacturing changes, and combination products than about new molecular entities. Commercial leverage typically comes from (1) brand-level differentiation in older products (bioavailability, dosing convenience), (2) fixed-dose combinations with trimethoprim or other agents where method and formulation patents can persist, and (3) ongoing FDA lifecycle management for specific dosage forms rather than new active ingredients. For investors and litigators, the main value inflection is timing: most monotherapies have long since lost composition-of-matter protection, pushing remaining patent enforcement toward product-specific IP and Paragraph IV risk management around the next wave of generic/authorized distributor substitution.

What patents protect sulfonamide antibacterial drugs and who owns the estate?

Is sulfonamide antibacterial patent protection mainly composition-of-matter or lifecycle patents

For most sulfonamide antibacterials, the near-universal pattern is:

• Composition-of-matter for core sulfonamide APIs is long expired for the majority of widely used agents.
• Remaining enforceable IP, where it exists, is concentrated in:
  • Dosage form and formulation patents (controlled release, crystal form/polymorph, particle size, solubilization, granulation).
  • Fixed-dose combination patents (e.g., trimethoprim plus sulfamethoxazole; other sulfonamide pairings).
  • Manufacturing method patents (wet granulation parameters, drying conditions, impurity profiles).
  • Medical use patents (narrow indications, dosing regimens) where granted.

Because the segment is mature, the practical “patent protection” question usually maps to: which specific dosage strength, delivery format, or combination is still covered, and in which jurisdiction.

Which patent holders typically show up in sulfonamide antibacterial families

Patent ownership commonly sits with:

• Original innovators from mid-20th century to early-2000s.
• Specialty brands that maintained stewardship via reformulations.
• Generic firms that acquired brand portfolios or filed improvements that later became their own enforcing assets.
• Licensees for combination products where one partner contributes the medical-use or formulation claims.

Key patent claim types that control exclusivity or enforcement

• Composition of sulfonamide derivatives: typically expired for older agents.
• Polymorph/crystal form: can remain enforceable if a new solid form was pursued late.
• Compositions: excipients, stabilizers, particle size distributions, and manufacturing residual limits.
• Method-of-manufacture: can delay generic approval for specific product processes, but is harder to enforce against generic ANDA product manufacturing unless the claim structure is robust.
• Methods of use: can survive if tightly tied to a still-protected indication or dosing regimen.
• Combination-specific claims: often the most commercially relevant in this class.

When does sulfonamide antibacterial exclusivity end and when can generics launch?

How exclusivity timelines typically work in the sulfonamide antibacterial segment

For mature sulfonamide antibacterial products, the relevant exclusivity gates are usually:

1. NCE/NDAs: generally not applicable to most older sulfonamides.
2. 505(b)(2) or reformulation approvals: can introduce limited exclusivity via granted labeling rights or changed conditions of approval.
3. Patent term: usually the dominant factor if any enforceable patent remains.
4. Pediatric exclusivity (6 months): occasionally relevant if a qualifying pediatric study exists for a still-active NDA/BLA.

In practice, most products behave like:

• Composition-of-matter expiration long passed.
• Remaining barriers come from formulation patents or combination packaging and dosing patents.

How Orange Book status drives generic timing

The operational answer for “when can generics launch” is: when the last listed patent covering the approved NDA product expires, and whether the NDA holder has obtained relevant exclusivity periods. Generic entrants generally time Paragraph IV filings around the expectation that:

• The listed patents are weak enough to lose on validity or non-infringement.
• Or the NDA holder settles to avoid prolonged litigation.

What is the Orange Book status of sulfonamide antibacterial drugs?

Which Orange Book listings matter most for this class

In sulfonamide antibacterials, Orange Book coverage typically concentrates on:

• Drug substance: the API.
• Drug product: strength-specific formulation, excipients, and dosage form.
• Methods: use or administration instructions linked to labeling.

How to read listings for generic risk

• If only drug product patents remain, generic approval is more likely to be feasible after expiration, but litigations still occur if the generic’s composition is argued to fall within claim scope.
• If drug substance patents still list, entry timelines become longer and more settlement-prone.
• If method-of-use patents are listed, generics can sometimes launch for non-covered indications if labeling can be carved out, but this depends on FDA labeling strategy and claim structure.

Which sulfonamide antibacterials face active Paragraph IV challenges?

What drives Paragraph IV filings in a mature sulfonamide segment

Paragraph IV challenges typically target:

• Combination products where formulation and ratio claims still have remaining life.
• Brand reformulations with later-life patents.
• Specific solid forms that generics may recreate but not exactly match.

What settlement patterns usually look like

Where settlement occurs, it often includes:

• Licensing of specific product presentations.
• A supply or distribution agreement.
• Carve-outs around dosage strengths, NDCs, or specific release profiles.

Litigation and outcome mechanics

In litigation-heavy cases, the commercial outcome is less about the underlying pharmacology and more about:

• Claim construction for formulation or method claims.
• Patent validity challenges based on obviousness or lack of novelty.
• Evidence that the generic product infringes the asserted claims (or does not).

How many formulation and polymorph patents cover sulfonamide antibacterial dosage forms?

Typical coverage structure by dosage form

• Tablets/capsules: often covered by excipient blends, granulation method, and dissolution specs.
• Suspensions: stability and reconstitution characteristics can create multiple product patents.
• Topicals (if applicable): though “sulfonamide antibacterial” marketing often focuses on systemic agents, topical sulfonamide antibacterials (where present) can add separate formulation and manufacturing protections.
• Combination products: frequently have more product patents due to fixed-dose ratios, compatibility, and stability.

What “polymorph coverage” means in practice

A “polymorph” strategy can produce:

• Multiple patents tied to specific solid forms.
• Limits on generic substitution if the generic uses a different solid form and the NDA holder argues equivalence falls inside claims.

What method-of-use patents cover sulfonamide antibacterial indications and dosing?

Where method-of-use patents show up

Method-of-use claims most often appear for:

• Specific dosing regimens designed to improve efficacy or minimize adverse outcomes.
• Specific patient populations or infection types.
• Label carve-outs where the brand maintains a differentiating indication.

How labeling strategy affects generic entry

A generic can sometimes:

• Launch for non-patented indications if FDA permits labeling carve-outs.
• Avoid infringement by omitting protected language, if the claims are tied to the protected instructions.

The litigation risk turns on:

• Whether the remaining label still practices the method claims.
• Whether the ANDA product is considered infringing despite labeling changes.

How do sulfonamide antibacterials compare with other older antibiotic classes on patent durability?

Relative patent durability

In mature antibacterial classes:

• Many penicillins and cephalosporins have fragmented, older estates tied to specific formulations and combination products.
• Sulfonamides behave similarly: durable value comes from lifecycle patents and combination formulations rather than active ingredient breakthroughs.

Competitive positioning

• Sulfonamides maintain strong generics penetration because APIs are stable to manufacture and historically widely prescribed.
• Brands that persist tend to do so through dosage convenience, stable brands, or combination IP.

What manufacturing and IP barriers block generic entry for sulfonamide antibacterials?

What barriers are most common

• Solid-state and impurity control: compliance with dissolution and impurity specs can become an infringement or design-around battleground.
• Process-dependent equivalence: if claims are directed to process steps, the generic’s manufacturing records matter.
• Stability and shelf-life: suspensions and combination products can be harder to replicate exactly.

How this plays in litigation

Even with expired composition-of-matter, enforcement often argues:

• The generic uses the same formulation composition.
• The generic falls within the claimed ranges for excipient concentrations.
• The generic’s manufacturing yields the same polymorph or particle distribution.

What FDA regulatory pathway issues affect sulfonamide antibacterial generic approvals?

ANDA feasibility

For many sulfonamide antibacterials, ANDAs are common since:

• The active ingredients are well understood.
• Bioequivalence can often be established.
• Formulation differences must still meet dissolution and stability.

505(b)(2) dependencies

If a brand uses a 505(b)(2) or relies on a listed drug with still-active patents for certain listed changes, generics can face longer regulatory sequencing.

Labeling carve-outs and patent certifications

If method-of-use or indication patents are listed:

• Generics may need Paragraph IV certifications for protected claims.
• Or they may pursue FDA labeling to avoid infringement (at a risk of being deemed an improper carve-out).

Commercial dynamics: why sulfonamide antibacterials still matter despite mature patents

Pricing and substitution

• The class is typically price-competitive with a strong substitutability profile.
• Formularies drive utilization to lowest net price products, shifting value away from brands once patents expire.

Procurement and inventory effects

Even when patents expire, the transition to lowest-cost product is shaped by:

• Inventory depletion.
• Contract renewals.
• Pharmacy benefit manager dynamics.
• Supply disruptions for particular strengths or dosage forms.

What creates pocket profitability

• Strength-specific patents that delay substitution for certain NDCs.
• Suspension products where generics face stability or bioequivalence hurdles.
• Combination products where ratio and formulation control is more defensible.

Key patent estate workstreams for investors, licensors, and litigators

1) Map patents by NDC-strength and dossier route

Sulfonamide antibacterial exclusivity risk must be evaluated at:

• NDC-level Orange Book coverage.
• Strength-specific product patents.
• Whether the referenced listed drug is protected.

2) Determine whether infringement theory is product-composition or process-dependent

• Composition-dependent claims are easier for infringement analysis if generic uses similar formulation.
• Process-dependent method claims depend on manufacturing and claim construction.

3) Forecast entry with a “last-to-expire plus litigation” model

• Assume some delay due to settlement or appeals.
• Track any pediatric exclusivity or patent term adjustments that extend term.

4) Evaluate settlement incentives

In a commoditized class, settlements are often driven by:

• Litigation duration costs.
• Price erosion risk from rapid market entry.
• Contracting and supply chain certainty.

Key Takeaways

• Sulfonamide antibacterial patent value is concentrated in lifecycle and combination product IP, not composition-of-matter.
• Orange Book listings still govern generic timing at the NDC-strength and formulation level.
• Paragraph IV risk is most likely where active patents remain on drug product, method-of-use, or combination compositions.
• Commercial outcomes depend on litigation timelines, settlement dynamics, and dossier route (ANDA vs 505(b)(2)) plus labeling carve-outs.

FAQs

1. Which sulfonamide antibacterial products are most vulnerable to near-term generic substitution based on Orange Book drug product patents?
2. Do method-of-use patents on sulfonamide antibacterials meaningfully delay ANDA approvals, or can labeling carve-outs avoid infringement?
3. How often do polymorph/crystal form patents appear in sulfonamide antibacterial formulation families, and how do they impact design-around strategies?
4. What settlement structures are most common in sulfonamide antibacterial Paragraph IV litigations, and how do they affect market entry dates?
5. For sulfonamide antibacterial suspensions and combination products, what formulation and manufacturing factors most affect bioequivalence and infringement arguments?

References

1. FDA. Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations. U.S. Food and Drug Administration.
2. FDA. Guidance for Industry: Paragraph IV Certifications and Other Aspects of the Hatch-Waxman Amendments. U.S. Food and Drug Administration.
3. FDA. Regulatory Information on 505(b)(2) Applications. U.S. Food and Drug Administration.
4. 21 U.S.C. § 355 (Hatch-Waxman framework). United States Code.