List of Excipients in Branded Drug DIFLUNISAL

Generic Drugs Containing DIFLUNISAL

Company	Ingredient	NDC	Excipient
Teva Pharmaceuticals USA Inc	diflunisal	0093-0755	CELLULOSE, MICROCRYSTALLINE
Teva Pharmaceuticals USA Inc	diflunisal	0093-0755	CROSCARMELLOSE SODIUM
Teva Pharmaceuticals USA Inc	diflunisal	0093-0755	FD&C BLUE NO. 2--ALUMINUM LAKE

What are the Most Frequently-Used Excipients in DIFLUNISAL?

# Of NDCs	Excipient
11	CELLULOSE, MICROCRYSTALLINE
11	CROSCARMELLOSE SODIUM
8	FD&C BLUE NO. 2

Diflunisal Excipient Strategy and Commercial Opportunities

Last updated: August 30, 2026

Diflunisal is an off-patent, nonsteroidal anti-inflammatory drug with limited current U.S. commercial momentum. Its main formulation challenge is the combination of a relatively high oral dose, weak-acid solubility behavior, and the need to control tablet size, dissolution, gastrointestinal tolerability, and manufacturing cost. The strongest commercial opportunities are low-cost immediate-release generics, differentiated rapid-release tablets, hospital or institutional supply, and selected international markets rather than premium branded products.

What is diflunisal and how is it regulated?

Diflunisal is a salicylic-acid derivative NSAID indicated for acute or chronic pain and osteoarthritis-related symptoms. The reference product, Dolobid, was marketed as 250 mg and 500 mg tablets. It is administered orally and is not a biologic, peptide, controlled substance, or injectable product.

Attribute	Diflunisal
Active ingredient	Diflunisal
Therapeutic class	NSAID; salicylic-acid derivative
Common strengths	250 mg and 500 mg
Original reference product	Dolobid
Route	Oral
Dosage form	Immediate-release tablet
U.S. regulatory pathway	Abbreviated New Drug Application for generics
Biosimilar exposure	None
Primary technical issue	Dissolution and dose loading
Current exclusivity profile	No meaningful modern U.S. regulatory exclusivity expected
Commercial status	Mature, genericized product with limited differentiation

The U.S. Food and Drug Administration approved Dolobid under NDA 018830. Current product availability depends on manufacturer and market. FDA labeling identifies gastrointestinal bleeding, renal toxicity, cardiovascular risk, and hypersensitivity as material safety considerations.[1]

What patents protect diflunisal?

Diflunisal is not generally protected by a commercially significant U.S. composition-of-matter patent estate. Its original product patents and regulatory exclusivities expired decades ago. A modern generic developer would normally focus on formulation equivalence, manufacturing controls, and market access rather than on overcoming an active compound patent.

Are diflunisal formulation patents still commercially relevant?

Potentially, but mainly outside the original product estate. A new patent could cover:

• A rapid-dissolution tablet using a specific disintegrant system.
• A diflunisal salt or co-crystal.
• A taste-masked suspension or orally disintegrating formulation.
• A gastroprotective or modified-release dosage form.
• A fixed-dose combination.
• A manufacturing process that improves particle-size control or dissolution.
• A pharmaceutical composition with a defined impurity profile.

These rights would need to satisfy novelty and non-obviousness requirements. A simple substitution of common excipients, such as replacing one superdisintegrant with another, would face a higher obviousness risk unless it produced an unexpected dissolution, stability, bioavailability, or manufacturability result.

What is the Orange Book status of diflunisal?

Diflunisal has historically been associated with the Dolobid reference product and generic tablet products. FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations, known as the Orange Book, remains the primary source for current reference-listed-drug and therapeutic-equivalence information.[2]

For commercial planning, the relevant issues are:

1. Whether a current reference-listed drug is available.
2. Whether a generic applicant can establish pharmaceutical equivalence to the applicable reference product.
3. Whether any listed patents or exclusivity remain active.
4. Whether the proposed product requires a suitability petition, clinical bridge, or alternative reference strategy.

Diflunisal is not expected to have active New Chemical Entity exclusivity. Any remaining Orange Book patent listing would require current transaction-level review before filing or launch decisions.

When does diflunisal lose exclusivity?

Diflunisal’s original regulatory and patent exclusivity expired long ago. It is a mature generic drug, not a protected launch product. Generic entry therefore does not depend on the expiration of a near-term exclusivity period.

What is the generic launch risk for diflunisal?

The principal risk is commercial erosion rather than patent litigation. A generic applicant would generally assess:

Risk area	Assessment
Compound patent	Low
Regulatory exclusivity	Low
Formulation patent	Product-specific
Paragraph IV exposure	Possible only if a relevant listed patent exists
Bioequivalence risk	Moderate, depending on dissolution behavior
Manufacturing risk	Moderate
Market-size risk	High
Price erosion	High in multi-supplier markets
Supply-chain risk	Moderate
Biosimilar risk	None

Diflunisal’s 250 mg and 500 mg strengths create a relatively high active load. That can constrain tablet compression, friability, disintegration, and tablet dimensions. These technical factors are more likely to delay a product than a patent dispute.

What excipients are suitable for diflunisal tablets?

A conventional immediate-release tablet should prioritize robust disintegration and reproducible dissolution. Diflunisal is a weak acid with limited intrinsic aqueous solubility, so excipient selection should support wetting, dispersion, and release across physiologically relevant pH conditions.

Recommended immediate-release excipient architecture

Function	Candidate excipients	Commercial rationale
Diluent	Microcrystalline cellulose, lactose monohydrate, dibasic calcium phosphate	Controls tablet size, flow, and compression
Dry binder	Microcrystalline cellulose, low-substituted hydroxypropyl cellulose	Supports mechanical strength
Superdisintegrant	Crospovidone, croscarmellose sodium, sodium starch glycolate	Improves tablet breakup and dissolution
Wetting aid	Sodium lauryl sulfate, poloxamer, selected surfactant systems	Supports dispersion of hydrophobic drug particles
Glidant	Colloidal silicon dioxide	Improves powder flow
Lubricant	Magnesium stearate, sodium stearyl fumarate	Controls ejection and sticking
Film coat	Hypromellose, polyethylene glycol, titanium dioxide or approved colorants	Improves swallowability and identification

The preferred first-screening platform would use microcrystalline cellulose with crospovidone or croscarmellose sodium, a low lubricant concentration, and a wetting strategy that does not create unacceptable stability or gastrointestinal concerns.

Which excipient risks require development attention?

Magnesium stearate can reduce tablet wettability when over-lubrication occurs. This is particularly relevant for a poorly soluble weak acid. Blending time and lubricant concentration should therefore be controlled as critical process parameters.

Sodium lauryl sulfate may improve wetting but can raise tolerability and regulatory questions if used at a high level. Crospovidone often provides rapid disintegration without the swelling-related variability sometimes associated with sodium starch glycolate. Croscarmellose sodium can be effective in direct compression but may be sensitive to particle-size distribution and formulation moisture.

Lactose-based systems can reduce cost but may produce different compaction and moisture behavior from microcrystalline-cellulose systems. Dibasic calcium phosphate can improve compactability and reduce tablet weight, but its higher density and water-insoluble character require dissolution optimization.

What formulation patents could create commercial differentiation?

The strongest patent opportunities are likely to involve measurable performance advantages rather than routine excipient combinations.

Rapid-release diflunisal tablet

A rapid-release product could combine particle-size engineering, a defined wetting agent, and a superdisintegrant system. Useful claim parameters could include:

• Dissolution at defined pH values.
• Time to reach a specified percentage dissolved.
• Particle-size distribution.
• Tablet hardness and disintegration time.
• Stability after accelerated storage.
• Reduced fed-versus-fasted variability.

A defensible patent would need data showing that the formulation produces an unexpected result compared with conventional diflunisal tablets.

Diflunisal salt or co-crystal

Salt or co-crystal development could improve dissolution, flow, tabletability, or dose uniformity. Commercial value would depend on whether the new form provides a clinically or manufacturing-relevant benefit. A salt that improves dissolution but increases hygroscopicity may shift risk from bioavailability to stability.

Orally disintegrating or taste-masked product

An orally disintegrating tablet could target patients with swallowing difficulty. The commercial opportunity is narrower because diflunisal is administered at a relatively high dose. A 500 mg orally disintegrating product would face substantial tablet-mass and mouthfeel constraints.

Taste masking would require attention to diflunisal’s sensory profile, coating load, disintegration delay, and patient acceptability. Ion-exchange resins, polymeric coatings, lipid matrices, and drug-loaded particles are possible approaches, but each adds manufacturing complexity.

Liquid suspension

A ready-to-use or reconstituted suspension could address patients unable to swallow tablets. The main challenges would be sedimentation, redispersibility, chemical stability, dose uniformity, preservative compatibility, and pH control. A suspension may be more commercially attractive in pediatric, geriatric, or institutional settings, but diflunisal’s safety profile limits broad pediatric positioning.

Gastroprotective or modified-release product

A delayed-release or gastroprotective formulation could seek to reduce local gastric exposure. It would not eliminate systemic NSAID risks, including gastrointestinal bleeding, renal injury, and cardiovascular events. A modified-release product would also require more complex pharmacokinetic and bioequivalence work than a standard immediate-release tablet.

How should a company design a diflunisal excipient screening program?

A practical development sequence would begin with the lowest-risk generic platform and then test differentiated options.

Stage 1: Immediate-release generic platform

The initial screen should compare:

1. Microcrystalline cellulose plus crospovidone.
2. Microcrystalline cellulose plus croscarmellose sodium.
3. Lactose or dibasic calcium phosphate blends.
4. Low-level surfactant versus no surfactant.
5. Magnesium stearate versus sodium stearyl fumarate.
6. Direct compression versus dry granulation.

Testing should include dissolution in multiple media, disintegration, hardness, friability, assay, content uniformity, impurities, and accelerated stability.

Stage 2: Bioequivalence risk reduction

Dissolution should be evaluated under pH conditions relevant to a weak-acid drug. The formulation should be compared with the applicable reference product across multiple lots where available. The development team should examine fed and fasted sensitivity, particle-size effects, and sensitivity to manufacturing scale.

Stage 3: Differentiated product

Only after the generic platform is stable should the company assess a premium formulation. The most credible options are a smaller tablet, faster dissolution, improved swallowability, or an institutional suspension. A new formulation should have a clear regulatory pathway and a target market willing to pay for the additional complexity.

Which companies are challenging diflunisal patents?

Diflunisal does not have the type of active, high-value patent contest associated with major contemporary brands. Generic manufacturers may enter through ANDAs, but the market is more likely to involve routine competition than visible Paragraph IV litigation.

What is the Paragraph IV risk?

Paragraph IV certification becomes relevant if an ANDA applicant identifies an unexpired patent listed for the reference product. For a mature product such as diflunisal, the probability of a material Paragraph IV event is lower than for recently approved drugs. A company should still verify the current Orange Book listing and any later-issued formulation or method-of-use patents before filing.

No biosimilar litigation is relevant because diflunisal is a small-molecule drug.

What litigation or settlement agreements affect diflunisal?

No widely recognized current U.S. litigation or settlement structure defines the diflunisal market. The commercial analysis should focus on product-specific notices, ANDA litigation records, patent-listing history, and any manufacturing or distribution agreements.

What licensing opportunities exist for diflunisal?

Licensing value is limited for a conventional tablet because the active ingredient is generic and price competition is substantial. Opportunities are more credible in defined technology areas:

• A proprietary diflunisal salt or co-crystal.
• A high-solubility particle-engineering platform.
• A stable oral suspension.
• A fixed-dose combination with a non-NSAID analgesic or gastroprotective agent.
• A formulation suitable for a geographically underserved market.
• A manufacturing process that lowers cost or improves supply reliability.

A licensee would need a defensible patent position, evidence of improved product performance, and a market with limited generic substitution. A routine excipient reformulation is unlikely to support a substantial upfront payment or royalty.

How large is the commercial opportunity for diflunisal?

The U.S. opportunity is likely a mature, low-margin generic market. Revenue potential depends on current supplier count, wholesaler contracts, reimbursement, shortage conditions, and the availability of the reference product. Public approval records alone do not establish a reliable current market size.

Geographic opportunities

Potentially attractive markets may include countries where:

• Diflunisal remains registered but has limited supplier competition.
• NSAID demand is stable.
• Local manufacturing incentives favor a domestic tablet producer.
• The reference product is unavailable or expensive.
• Hospital procurement rewards reliable supply rather than brand promotion.

Market entry should be screened country by country because registration status, reference-product requirements, permitted excipients, trademark rights, and pharmacopoeial standards differ.

Revenue exposure

A standard generic diflunisal tablet would likely face rapid price erosion if several suppliers are active. A differentiated product could command better economics only if it achieves one of the following:

• FDA-approved labeling differentiation.
• A patentable formulation advantage.
• Reliable supply during competitor shortages.
• A meaningful reduction in tablet burden.
• Access to a channel that values specialized dosage forms.

The most defensible business case is usually operational: efficient manufacturing, low-cost sourcing, and dependable distribution.

How strong is the diflunisal patent estate?

The legacy patent estate is weak as a barrier to standard generic entry. The prospective estate for a new formulation could be moderate if it includes:

• Composition claims with narrow but reproducible excipient ranges.
• Performance claims tied to dissolution or stability.
• Process claims that are difficult to design around.
• Multiple independent claim types.
• Data showing a clinically relevant benefit.

A single broad claim covering a conventional diflunisal tablet would face substantial validity and obviousness risk. A layered estate covering composition, process, particle attributes, and dosage-form performance would provide stronger protection.

Key Takeaways

• Diflunisal is a mature, genericized oral NSAID with no biosimilar pathway.
• Patent risk is low for the active ingredient and high only if a new formulation creates enforceable rights.
• The central technical challenge is achieving reproducible dissolution at a relatively high dose.
• Microcrystalline cellulose, crospovidone or croscarmellose sodium, controlled lubrication, and targeted wetting are logical starting points.
• Rapid-release tablets, suspensions, salt forms, and co-crystals offer the clearest formulation opportunities.
• U.S. commercial potential is likely limited and price-sensitive.
• International supply, institutional products, and differentiated dosage forms may offer better returns than a conventional U.S. generic.
• A premium licensing strategy requires demonstrated performance and a patent estate stronger than a routine excipient substitution.

FAQs About Diflunisal Excipient and Commercial Strategy

Can diflunisal be formulated as an oral suspension?

Yes. A suspension could target patients who cannot swallow tablets, but it would require work on sedimentation, redispersibility, dose uniformity, stability, preservative compatibility, and pH control.

Is diflunisal suitable for an orally disintegrating tablet?

It is technically possible, but the 250 mg and 500 mg dose strengths make tablet mass, mouthfeel, and taste masking difficult. A lower-strength or multiparticulate presentation may be more practical.

Which excipient is most important for diflunisal dissolution?

No single excipient determines performance. Superdisintegrant selection, particle size, wetting, compression force, and lubricant level interact. Crospovidone or croscarmellose sodium is a logical starting point for screening.

Can a diflunisal formulation obtain new patent protection?

Yes, if the formulation provides a novel and non-obvious composition or manufacturing result. Routine substitution of standard tablet excipients is less likely to support strong claims.

Is diflunisal a viable drug for a fixed-dose combination?

Possibly, but safety and labeling constraints are significant. A combination would need a clear clinical rationale, compatible dosing, evidence of additive benefit, and controls for the gastrointestinal, renal, and cardiovascular risks associated with NSAID therapy.

References

1. U.S. Food and Drug Administration. (n.d.). Dolobid (diflunisal) prescribing information. FDA.
2. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
3. U.S. National Library of Medicine. (n.d.). Diflunisal drug label information. DailyMed.
4. United States Pharmacopeia. (2024). United States Pharmacopeia and National Formulary. U.S. Pharmacopeial Convention.