NALIDIXIC ACID Drug Patent Profile

Which patents cover Nalidixic Acid, and when can generic versions of Nalidixic Acid launch?

Nalidixic Acid is a drug marketed by Sun Pharm Industries and Watson Labs and is included in six NDAs.

The generic ingredient in NALIDIXIC ACID is nalidixic acid. There are two drug master file entries for this compound. Additional details are available on the nalidixic acid profile page.

Summary for NALIDIXIC ACID

US Patents:	0
Applicants:	2
NDAs:	6

US Patents and Regulatory Information for NALIDIXIC ACID

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Sun Pharm Industries	NALIDIXIC ACID	nalidixic acid	TABLET;ORAL	070272-001	Jun 29, 1988		DISCN	No	No
Watson Labs	NALIDIXIC ACID	nalidixic acid	TABLET;ORAL	071919-001	Jun 29, 1988		DISCN	No	No
Sun Pharm Industries	NALIDIXIC ACID	nalidixic acid	TABLET;ORAL	070270-001	Jun 29, 1988		DISCN	No	No

Nalidixic Acid Investment Analysis: Patent Status, Market Fundamentals, Regulatory Risk, and Generic Outlook

Last updated: August 1, 2026

Nalidixic acid is a legacy first-generation quinolone with limited commercial value, no meaningful patent exclusivity, substantial antimicrobial-resistance pressure, and weak prospects for product-level investment. Its remaining value is concentrated in low-cost generic supply, selected urinary-tract infection markets, and possible institutional or geographic niches. The investment case is defensive and operational rather than growth-oriented.

What is nalidixic acid and how does it work?

Nalidixic acid is a synthetic antibacterial agent that inhibits bacterial DNA gyrase and topoisomerase IV. It was developed in the 1960s and became one of the earliest quinolone antibiotics used for urinary-tract infections caused by susceptible Gram-negative bacteria.

The drug is generally associated with:

Attribute	Nalidixic acid
Drug class	First-generation quinolone
Primary historical use	Urinary-tract infections
Target	Bacterial DNA gyrase and topoisomerase IV
Typical dosage form	Oral tablets or suspension, depending on market
Therapeutic position	Legacy antibacterial
Biosimilar relevance	None
Patent relevance	Historical only
Current commercial structure	Generic and regionally variable
Main commercial constraint	Resistance and substitution by newer antibiotics

Nalidixic acid has a narrower spectrum and less favorable clinical profile than later fluoroquinolones. Resistance can arise through mutations in DNA gyrase or topoisomerase genes and through reduced bacterial permeability or increased efflux. The drug is therefore less competitive in markets where clinicians have access to newer agents.

The historical U.S. product was marketed as NegGram. The FDA labeling identified nalidixic acid for urinary-tract infections caused by susceptible organisms and included warnings concerning central nervous system effects, seizures, cartilage and tendon concerns associated with quinolone-class drugs, and use restrictions in pediatric patients.[1]

What patents protect nalidixic acid?

Nalidixic acid has no commercially meaningful composition-of-matter patent protection. The original discovery and development patents expired decades ago.

Patent category	Current investment relevance
Active ingredient patent	Expired
Basic pharmaceutical composition	Expired
Original use patent	Expired or legally immaterial
Salt or polymorph protection	No established strategic moat
Formulation patent	No widely recognized blocking estate
Manufacturing patent	Potentially local and process-specific, but not a broad market barrier
Pediatric or dosing patent	No material current exclusivity position
Orphan-drug exclusivity	None identified
Patent-term extension	Not relevant to the legacy product

A current manufacturer may hold process know-how, supplier agreements, manufacturing specifications, or regulatory dossiers. Those assets can create operational advantages, but they do not recreate patent exclusivity over nalidixic acid.

When did nalidixic acid lose exclusivity?

Nalidixic acid lost meaningful market exclusivity long before the modern generic-drug framework became the primary commercial model. The product entered clinical use in the 1960s, and the relevant basic patents are now historical.

The commercial timeline is therefore different from that of a modern small-molecule product:

Period	Commercial development
1960s	Clinical introduction and initial use in urinary-tract infections
1970s-1980s	Broader availability of generic products and later quinolones
1990s	Increasing substitution by fluoroquinolones and other urinary antibiotics
2000s	Declining strategic importance in developed markets
2010s-present	Continued use in selected markets, but with limited differentiation

There is no commercially significant future patent cliff comparable to a branded drug approaching loss of exclusivity. The product is already in the post-exclusivity phase.

What is the Orange Book status of nalidixic acid?

The FDA Orange Book is not a source of current branded exclusivity for nalidixic acid. Historical U.S. marketing under NegGram does not create a current patent barrier for generic manufacturers.

The relevant commercial conclusions are:

• Nalidixic acid is not supported by a current U.S. composition patent.
• A generic applicant would not face a modern branded patent estate comparable to those surrounding protected antibiotics.
• Paragraph IV litigation is not a central risk for the active ingredient.
• Any U.S. regulatory pathway would depend primarily on an abbreviated new drug application, product availability, bioequivalence requirements, manufacturing compliance, and whether an approved reference product remains suitable for comparison.
• Product discontinuation or limited reference-product availability can create regulatory complexity even when patent risk is negligible.

The FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations, commonly called the Orange Book, remains the principal source for U.S. reference-product and therapeutic-equivalence information.[2] A historical product listing should not be treated as evidence of current commercial demand or active patent protection.

How many patents cover nalidixic acid?

No meaningful number of active, broad patents is expected to cover the nalidixic acid molecule itself. The relevant patent landscape is better described as expired foundational protection plus possible narrow manufacturing or formulation rights.

A prospective manufacturer should distinguish among four categories:

1. Expired molecule patents, which do not restrict entry.
2. Local process patents, which may affect a particular manufacturing route.
3. Regulatory exclusivity or reference-product issues, which are not patent rights.
4. Trade secrets and quality systems, which can affect cost and supply reliability.

The principal barrier is not freedom to operate around the active ingredient. It is whether the product can be manufactured economically, registered in the target jurisdiction, and sold into a market where prescribers still use it.

What formulations are protected by nalidixic acid patents?

No widely recognized current formulation estate gives nalidixic acid a durable commercial advantage. Historical products used conventional oral dosage forms. Tablets, capsules, and suspensions are technically straightforward compared with controlled-release delivery systems, sterile injectables, liposomal products, or complex biologics.

Potential formulation work could involve:

• Taste masking for oral liquid products.
• Improved dissolution or suspension stability.
• Pediatric dosing flexibility.
• Packaging with longer shelf life.
• Fixed-dose combinations.
• Modified-release oral delivery.

These opportunities have limited value unless they solve a documented regulatory or supply problem. A formulation patent would also need sufficient commercial demand to justify development, registration, manufacturing validation, and postapproval obligations.

What is the FDA regulatory status of nalidixic acid?

Nalidixic acid has a long regulatory history but a weak current U.S. commercial position. The historical FDA-approved product was indicated for susceptible urinary-tract infections. Current use must account for antimicrobial-resistance patterns, updated prescribing standards, and the status of locally authorized products.

Regulatory risks include:

• Lack of a current or commercially viable U.S. reference product.
• Difficulty demonstrating a clear clinical role against modern alternatives.
• Manufacturing compliance for a low-volume legacy product.
• Labeling requirements for quinolone-class safety risks.
• Changing antimicrobial-stewardship policies.
• Country-specific requirements for efficacy, resistance surveillance, and pharmacovigilance.

The FDA has repeatedly emphasized antimicrobial stewardship and the risks associated with inappropriate antibacterial use. Those policies reduce the strategic attractiveness of older antibiotics that lack a clear advantage over better-supported alternatives.[3]

Which companies are challenging nalidixic acid exclusivity?

No major branded company appears to have a current exclusivity position worth challenging. The competitive field consists primarily of generic manufacturers, regional pharmaceutical companies, contract manufacturers, and API suppliers.

The likely competitive dimensions are:

Competitive factor	Effect on investment
API price	High impact because the product is commoditized
Manufacturing scale	Favors established generic suppliers
Regulatory registrations	Creates country-level switching costs
Product availability	Can support temporary pricing power during shortages
Brand recognition	Limited outside legacy markets
Clinical differentiation	Weak
Patent position	Minimal
Distribution reach	More important than intellectual property

A potential entrant would compete against existing registrations and supply relationships rather than a single patent holder. This makes market access and procurement contracts more important than litigation strategy.

What generic entry risks exist for nalidixic acid?

Generic entry risk is structurally high because the active ingredient is old, the patent estate is weak, and conventional oral formulations are relatively simple.

The main generic-entry scenarios are:

Low-price commodity entry

Several suppliers compete for government tenders, hospital contracts, or pharmacy distribution. Margins compress rapidly, and the lowest-cost compliant manufacturer gains share.

Regional shortage opportunity

A supplier may obtain temporary pricing leverage if an incumbent exits, an API plant experiences disruption, or a country maintains demand despite limited supply. This is a supply-arbitrage opportunity, not a durable moat.

Regulatory revival

A manufacturer could seek registration in a market where nalidixic acid remains listed in national treatment protocols. The opportunity depends on local demand, resistance data, and procurement practices.

Reformulation strategy

An oral suspension or pediatric formulation could address a local access problem. The commercial opportunity would remain limited unless the product has regulatory or distribution advantages.

How strong is the patent estate for nalidixic acid?

The patent estate is weak for investment purposes.

Patent-strength factor	Assessment
Composition-of-matter protection	None of practical current value
Remaining patent term	None of practical current value
Formulation protection	Limited or unestablished
Method-of-use protection	Historical and non-blocking
Manufacturing protection	Potentially narrow
Litigation leverage	Low
Exclusivity duration	No meaningful remaining period
Ability to support premium pricing	Very low

The product’s defensibility must come from manufacturing cost, regulatory registrations, distribution, supply reliability, or access to a scarce API. None of these is equivalent to patent exclusivity.

What patent litigation affects nalidixic acid?

Nalidixic acid is unlikely to generate material contemporary patent litigation. The molecule is too old to support a conventional Paragraph IV litigation strategy against a branded innovator.

Potential disputes would more likely concern:

• Contract manufacturing obligations.
• Trademark ownership.
• Regulatory dossier access.
• Bioequivalence or product-quality findings.
• API specifications.
• Procurement exclusion.
• Anticompetitive conduct among suppliers.

These disputes could affect individual companies but would not normally change the value of the nalidixic acid market as a whole.

Are there licensing deals for nalidixic acid?

Nalidixic acid is unlikely to generate meaningful current licensing activity around the molecule. Any licensing value would arise from:

• Regional marketing rights.
• Product registrations.
• API supply agreements.
• Contract manufacturing.
• Distribution partnerships.
• Portfolio transfers involving legacy anti-infectives.

A licensing transaction should be assessed as a supply or market-access deal. Royalty economics based on proprietary drug technology are unlikely to be attractive.

How does nalidixic acid compare with modern urinary-tract antibiotics?

Nalidixic acid is commercially disadvantaged against newer therapies in most developed markets.

Factor	Nalidixic acid	Modern alternatives
Spectrum	Narrow	Often broader or better targeted
Resistance position	Vulnerable	Varies by agent and local data
Clinical familiarity	Historical	Current guideline support is stronger for selected agents
Formulations	Conventional oral	More diverse
Patent protection	None	Some products may retain protection
Pricing	Low	Can range from generic to premium branded
Stewardship position	Constrained	Depends on pathogen and indication
Commercial growth	Limited	Higher for differentiated or guideline-preferred products

The relevant comparators may include nitrofurantoin, trimethoprim-sulfamethoxazole, fosfomycin, beta-lactams, and later fluoroquinolones. Choice depends on pathogen susceptibility, patient characteristics, local resistance, and regulatory labeling.

Nalidixic acid’s low price is not enough to offset weak demand if physicians and procurement bodies have moved to alternatives.

What revenue exposure does nalidixic acid create?

Revenue exposure is usually immaterial at the multinational portfolio level unless the company has a concentrated legacy-generic business in a market where the product remains routinely prescribed.

A manufacturer’s exposure may be meaningful when:

• The product is included in public tenders.
• The company owns the only local registration.
• The API supply chain is integrated.
• The product is sold with other legacy anti-infectives.
• The market has limited access to alternative antibiotics.

Public companies generally do not report nalidixic acid revenue as a separate line item. Financial analysis should therefore examine the broader anti-infective or established-products segment, not attempt to value nalidixic acid as an independently disclosed growth asset.

What manufacturing and intellectual-property barriers exist?

Manufacturing barriers are moderate operationally but low technologically. The active ingredient is established, and the dosage forms are conventional. The more important requirements are:

• GMP-compliant API and finished-dose production.
• Validated impurity controls.
• Reliable analytical methods.
• Stability data.
• Consistent dissolution performance.
• Qualified suppliers.
• Country-specific registration.
• Pharmacovigilance and complaint handling.

The API market may be more concentrated than the finished-dose market. That can create temporary supply risk, especially where only a small number of facilities maintain active regulatory files.

The main intellectual-property risk is process-specific. A manufacturer must avoid protected process claims in the countries where it produces or sells the product. Because the basic molecule is old, a conventional freedom-to-operate review is generally more manageable than for a recently approved small molecule.

What is the investment scenario for nalidixic acid?

Nalidixic acid does not support a conventional branded-pharmaceutical investment thesis. The most credible scenarios are:

Scenario	Probability profile	Investment implication
Stable legacy demand	Most credible	Low-growth cash-flow product
Generic price erosion	High	Margin pressure
Regional supply shortage	Possible	Temporary pricing opportunity
New formulation success	Low	Requires targeted market need
Major patent value creation	Very low	No evident basis
Broad U.S. relaunch	Low	Regulatory and commercial execution risk
Portfolio acquisition	Possible	Value depends on registration and supply assets

An acquisition could make sense if the target owns multiple legacy products, has low-cost API access, or controls registrations in underserved markets. Nalidixic acid alone is unlikely to justify a substantial valuation premium.

The appropriate valuation framework is a low-multiple established-products model based on:

• Net sales by country.
• Gross margin after API and compliance costs.
• Tender duration.
• Registration status.
• Supply concentration.
• Product discontinuation risk.
• Working-capital requirements.
• Expected price erosion.
• Regulatory remediation costs.

Patent-based terminal value should be assigned little or no weight.

Key Takeaways

• Nalidixic acid is a legacy first-generation quinolone with no meaningful current composition-of-matter exclusivity.
• The drug’s historical patents expired decades ago.
• Current Orange Book relevance is limited to historical reference-product and regulatory information, not market exclusivity.
• Paragraph IV litigation and branded patent challenges are not material investment risks.
• No biosimilar opportunity exists because nalidixic acid is a conventional small molecule.
• Commercial demand is constrained by antimicrobial resistance, newer antibiotics, and stewardship policies.
• Conventional oral formulations have limited technical differentiation.
• The strongest investment rationale is a low-cost generic or regional supply platform, not a proprietary drug asset.
• Revenue exposure is likely to be small and embedded within broader generic or established-product portfolios.
• A nalidixic acid investment should be valued on manufacturing economics, registrations, supply reliability, and regional demand.

Frequently Asked Questions

Is nalidixic acid still commercially available?

It remains available in selected countries and markets, but availability is uneven. Its commercial presence is much weaker than that of newer urinary-tract antibiotics.

Can a company patent a new nalidixic acid formulation?

A new formulation may qualify for patent protection if it satisfies novelty, inventive-step, and other national requirements. Commercial value would depend on a specific clinical or manufacturing advantage.

Is nalidixic acid covered by FDA pediatric exclusivity?

There is no commercially meaningful current pediatric exclusivity position associated with nalidixic acid.

Could nalidixic acid become valuable during an antibiotic shortage?

A shortage could create temporary regional pricing power if nalidixic acid is locally authorized and pathogens remain susceptible. Resistance and treatment-guideline constraints would limit the duration and scale of that opportunity.

Is nalidixic acid a target for pharmaceutical licensing?

It may appear in regional supply, distribution, or legacy-product transactions. It is unlikely to support a high-value licensing deal based on proprietary technology or patent rights.

References

1. U.S. Food and Drug Administration. (n.d.). NegGram (nalidixic acid) prescribing information. FDA.

2. U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations. FDA.

3. U.S. Food and Drug Administration. (2017). FDA’s new regulatory strategy to improve antimicrobial stewardship. FDA.