List of Excipients in Branded Drug ZYFLO

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Chiesi USA Inc	ZYFLO	zileuton	10122-901	CELLULOSE, MICROCRYSTALLINE
Chiesi USA Inc	ZYFLO	zileuton	10122-901	CROSPOVIDONE
Chiesi USA Inc	ZYFLO	zileuton	10122-901	HYDROXYPROPYL CELLULOSE
Chiesi USA Inc	ZYFLO	zileuton	10122-901	HYPROMELLOSES
Chiesi USA Inc	ZYFLO	zileuton	10122-901	MAGNESIUM STEARATE
Chiesi USA Inc	ZYFLO	zileuton	10122-901	PROPYLENE GLYCOL
Chiesi USA Inc	ZYFLO	zileuton	10122-901	SODIUM STARCH GLYCOLATE TYPE A POTATO

ZYFLO Excipient Strategy and Commercial Opportunities for Zileuton

Last updated: August 25, 2026

Zyflo is the former U.S. brand for zileuton, a 5-lipoxygenase inhibitor used for chronic asthma management. The commercial opportunity is primarily generic or reformulated oral delivery rather than biosimilar development. The strongest product concepts are an extended-release tablet with improved adherence, a lower-pill-burden formulation, and a patient-friendly liquid or sprinkle product.

Zileuton has no biologic complexity and does not present biosimilar risk. Its main commercial constraints are liver-function monitoring, historic dosing frequency, competition from montelukast, and the need to demonstrate acceptable bioequivalence or clinical bridging for any modified-release product.

What is Zyflo and what drug does it contain?

Zyflo contains zileuton, a selective inhibitor of 5-lipoxygenase. The drug reduces leukotriene synthesis and was approved for chronic asthma treatment, not for acute bronchospasm relief.

Attribute	Zyflo / zileuton
Active ingredient	Zileuton
Therapeutic class	5-lipoxygenase inhibitor
Original dosage form	Immediate-release oral tablet
Extended-release brand	Zyflo CR
Original immediate-release strength	600 mg
Original immediate-release regimen	600 mg four times daily
Extended-release regimen	1,200 mg twice daily, administered as two 600 mg tablets per dose
Regulatory pathway	FDA NDA products
Biologic or small molecule	Small molecule
Biosimilar pathway	Not applicable
Main safety monitoring	Hepatic transaminases
Main commercial competitors	Montelukast, zafirlukast, inhaled corticosteroids and combination inhalers

The original immediate-release regimen created a significant adherence disadvantage. Zyflo CR addressed dosing frequency but retained a high total daily dose and a two-tablet administration at each dosing time. Those characteristics define the principal excipient and formulation opportunity.

What is the FDA regulatory status of Zyflo?

The FDA approved immediate-release Zyflo under NDA 20-862 and later approved Zyflo CR under NDA 21-645. The products were approved for chronic asthma prophylaxis and were not labeled as rescue treatments.[1][2]

The FDA has listed the Zyflo products as discontinued from marketing. A discontinued marketing status does not by itself establish a safety withdrawal. It indicates that the branded product is no longer marketed under the relevant NDA status.[3]

Regulatory issue	Commercial implication
Original NDA approval	Establishes a reference product history for generic development
Brand discontinuation	Opens potential supply and substitution opportunities
No biologic component	Eliminates biosimilar development requirements
Existing FDA labeling	Provides a clinical and safety benchmark
Hepatic monitoring requirement	Raises development and prescribing friction
Chronic-use indication	Supports maintenance-therapy positioning rather than acute-care positioning

A current applicant would need to determine whether a reference-listed drug remains active for the proposed product and whether the relevant product should be pursued through an ANDA, a 505(b)(2) application, or another FDA pathway. The pathway depends on whether the applicant copies an existing reference formulation or introduces a materially different release profile, dosage form, strength, or administration method.[4]

When does Zyflo lose exclusivity and patent protection?

Zileuton’s original small-molecule and branded-product exclusivity periods have expired. The commercial barrier is therefore unlikely to be a surviving basic-compound patent. The relevant barriers are product-specific patents, formulation patents, regulatory exclusivity, FDA reference-product status, and the cost of demonstrating bioequivalence.

The original NDA dates place the five-year new chemical entity exclusivity period in the late 1990s or early 2000s, depending on the date used for the original approval record. Any such exclusivity has long expired. A current applicant should focus on Orange Book patent listings associated with the relevant reference product and on the regulatory status of any active ANDA applicant.[3][5]

Are there active Orange Book patents for Zyflo?

The Orange Book, rather than historical brand literature, is the controlling source for listed patent and exclusivity information. Zyflo’s commercial opportunity should not be valued on the assumption that an old brand patent blocks entry. The practical analysis is:

1. Identify the active reference-listed drug for zileuton.
2. Review listed patents for immediate-release and extended-release products.
3. Confirm patent expiration dates and any pediatric extensions.
4. Check whether listed patents cover the active ingredient, formulation, method of use, or manufacturing process.
5. Review the FDA paragraph IV certification and litigation history for any proposed ANDA.

No biosimilar-type exclusivity applies because zileuton is a chemically synthesized small molecule.

What excipients are used in Zyflo tablets?

The original product labeling identifies inactive ingredients for the approved tablet products. Excipient selection differs between immediate-release and extended-release dosage forms, because the immediate-release product must disintegrate rapidly while the controlled-release product must regulate drug release over a prolonged period.[1][2]

The commercial value of the historical excipient system is limited. A generic applicant generally seeks Q1/Q2 similarity where required, but a new product can pursue a differentiated formulation if it accepts the additional regulatory burden.

Immediate-release excipient strategy

An immediate-release zileuton tablet would typically require:

• A diluent to support tablet mass and content uniformity.
• A binder to provide mechanical strength.
• A superdisintegrant to promote rapid tablet breakup.
• A lubricant to control ejection force.
• A wetting agent or surfactant if dissolution is limited by poor wetting.
• A film coat for swallowability, identification, and moisture protection.

A practical platform could use microcrystalline cellulose or lactose as the primary diluent, povidone or low-substituted hydroxypropyl cellulose as a binder, croscarmellose sodium or crospovidone as the disintegrant, and magnesium stearate as the lubricant.

The formulation should avoid excessive hydrophobic lubrication. Over-lubrication can slow dissolution and increase batch-to-batch variability. Zileuton tablets should be tested under multiple dissolution conditions because a formulation that meets a single compendial method may still show clinically relevant differences under fed and fasted conditions.

Extended-release excipient strategy

The strongest excipient opportunity is a once-daily or lower-pill-burden modified-release product. The reference extended-release product used a high-dose twice-daily regimen, leaving room for development work around matrix efficiency and dose consolidation.

A hydrophilic matrix could use hypromellose as the primary release-controlling polymer. The release profile can be adjusted through:

• Polymer viscosity grade.
• Polymer loading.
• Tablet porosity.
• Compression force.
• Drug-to-polymer ratio.
• Use of a second polymer or insoluble matrix former.

Hydrophobic matrix systems using ethylcellulose or lipid excipients may improve robustness against agitation and food-related changes, but they can complicate scale-up and dissolution control. Multiparticulate systems based on coated pellets can provide more flexible release engineering and may support sprinkle administration, but they increase manufacturing cost and process complexity.

The target should not be a nominally slower tablet. It should be a product with:

• Lower peak-to-trough fluctuation.
• Reliable exposure across fed and fasted conditions.
• No dose dumping.
• Acceptable tablet size.
• Lower daily pill burden.
• Comparable or improved hepatic safety monitoring burden.

What formulations are protected or commercially attractive for zileuton?

Once-daily extended-release tablets

A once-daily product would offer the clearest adherence proposition. The challenge is dose loading. Zileuton’s total daily dose and pharmacokinetic profile may require a large tablet or a multi-unit system.

A once-daily matrix tablet would need robust control of:

• Initial burst release.
• Late-stage release failure.
• Food-induced acceleration.
• Tablet size.
• Mechanical strength.
• Content uniformity at high drug loading.

A successful product could compete on convenience rather than price alone. Any once-daily claim would require regulatory support through appropriate pharmacokinetic studies and, depending on the proposed pathway, potentially additional clinical data.

Sprinkle or multiparticulate formulation

A sprinkle product could address patients who have difficulty swallowing large tablets. Enteric or extended-release coated pellets could be filled into capsules or packaged in unit-dose sachets.

The key excipient and process issues are:

• Taste masking.
• Protection of the release coating during administration.
• Avoidance of crushing or chewing.
• Stability under high humidity.
• Compatibility with soft foods.
• Dose recovery from the administration vehicle.

This product would have a stronger 505(b)(2) profile than a conventional ANDA if the dosage form or administration instructions differ materially from the reference product.

Oral liquid

An oral solution or suspension could target pediatric, geriatric, and dysphagic patients. The product is technically more difficult because zileuton’s aqueous solubility, taste, chemical stability, and dose volume must be controlled.

Potential excipient systems include:

• pH adjustment to improve solubility or stability.
• Cosolvents such as polyethylene glycol or propylene glycol.
• Surfactants for wetting.
• Suspending agents such as xanthan gum or microcrystalline cellulose-carboxymethylcellulose.
• Sweeteners and flavors for taste masking.
• Preservatives for multidose packaging.
• Chelators or antioxidants if oxidative degradation is observed.

A suspension may be more realistic than a high-concentration solution if solubility limits produce an unacceptable excipient load. Dose uniformity after storage and shaking would be central to approval.

Fixed-dose combination

A fixed-dose combination with another asthma therapy is commercially possible but strategically difficult. Zileuton’s mechanism differs from leukotriene receptor antagonists, but combination claims would need clinical justification. Combining zileuton with an inhaled corticosteroid, long-acting bronchodilator, or montelukast would create substantial clinical, regulatory, and intellectual-property complexity.

The more practical near-term opportunity is a differentiated zileuton dosage form rather than a new combination product.

How strong is the patent estate for Zyflo formulations?

The patent position should be viewed in three layers:

Patent layer	Likely relevance
Zileuton compound patents	Historical protection; expected to be expired
Original tablet formulation patents	Limited blocking power unless still listed and enforceable
Modified-release, sprinkle, liquid, or combination patents	Potentially meaningful for a new entrant or reformulator

A new developer can create defensible intellectual property around:

• Polymer ratios and release kinetics.
• Food-effect reduction.
• Multiparticulate coating architecture.
• Taste-masking systems.
• High-load tablet compression.
• Moisture-control packaging.
• Stability-enhancing excipient combinations.
• Once-daily pharmacokinetic profiles.
• Specific methods of treating asthma with the new dosage form.

Patent strength will depend on whether the claims require a narrow excipient combination or instead cover measurable product attributes such as dissolution ranges, pharmacokinetic parameters, or stability performance. Narrow composition claims may be easier to design around. Product-by-process claims are generally less attractive unless the process produces a distinct, measurable product.

What generic entry risks exist for Zyflo?

The main generic entry risks are regulatory and commercial.

Paragraph IV challenges

An ANDA applicant can file with a paragraph IV certification against a listed patent. The reference sponsor may respond with patent litigation, triggering the statutory stay under the Hatch-Waxman framework. The risk is material only if an active Orange Book-listed patent remains relevant to the proposed product.[5]

For a conventional immediate-release zileuton tablet, the applicant’s litigation exposure is likely lower than for a new extended-release or multiparticulate product. A differentiated formulation may avoid old patents but create new infringement exposure if a later sponsor has obtained listed or non-listed formulation patents.

Bioequivalence risk

Immediate-release bioequivalence may be relatively straightforward if the product matches the reference strength and release characteristics. Extended-release bioequivalence is more demanding. Studies may need to evaluate:

• Single-dose pharmacokinetics.
• Multiple-dose steady state.
• Fed and fasted conditions.
• Peak concentration.
• Area under the curve.
• Partial area metrics.
• Dose-dumping behavior.

A product with a lower daily dose or once-daily administration may not qualify for a simple ANDA, particularly if the reference product does not establish the same release profile.

Safety and prescribing risk

The FDA labeling for zileuton includes liver-function monitoring and warnings related to hepatic effects.[1][2] This requirement limits broad primary-care adoption and can make a lower-cost generic less attractive than montelukast, which has a simpler monitoring profile despite its own safety considerations.

How does Zyflo compare with montelukast and zafirlukast?

Factor	Zileuton	Montelukast	Zafirlukast
Mechanism	5-lipoxygenase inhibition	Leukotriene receptor antagonism	Leukotriene receptor antagonism
Dosing convenience	Historically four times daily IR; twice daily CR	Usually once daily	Usually twice daily
Liver monitoring	Important commercial issue	Not typically routine transaminase monitoring	Hepatic safety considerations
Formulation opportunity	High, because dosing burden is a weakness	Lower, because generic once-daily supply is established	Moderate
Generic competition	Possible but commercially niche	Intense	Established but smaller
Main differentiation route	Modified release, lower pill burden, liquid or sprinkle	Price, combination, pediatric formats	Price and tolerability
Biosimilar risk	None	None	None

Zileuton’s clinical differentiation is mechanistic, but its commercial differentiation must be formulation-driven. A product that preserves the existing high pill burden without lowering cost has limited strategic value.

Which companies are challenging or commercializing Zyflo?

Zyflo was historically associated with Abbott and later commercialized by Cornerstone Therapeutics, which promoted Zyflo CR in the United States. The brand products are no longer the central commercial vehicle for zileuton.

The relevant competitive set now includes:

• ANDA applicants for immediate-release zileuton.
• Potential applicants for extended-release zileuton.
• Contract manufacturers with high-dose tablet and modified-release capabilities.
• Specialty generic companies serving asthma and respiratory portfolios.
• Formulation licensors with multiparticulate or taste-masking platforms.

Publicly reported revenue exposure for Zyflo is limited because the product is no longer a major actively marketed branded asset. A valuation should therefore use scenario analysis rather than historical brand revenue. The most relevant variables are annual treated-patient volume, generic net price, formulary access, monitoring-related discontinuation, and the cost of pivotal bioequivalence studies.

What commercial opportunities exist for zileuton excipients?

The highest-value opportunity is a differentiated extended-release system that reduces daily administration from four immediate-release doses to one or two doses. The product should be positioned around adherence, dose convenience, and stable exposure.

A tiered portfolio could include:

1. A low-cost immediate-release generic tablet.
2. A two-tablet-per-day extended-release tablet.
3. A once-daily high-load matrix or multiparticulate product.
4. A sprinkle capsule for swallowing difficulty.
5. A flavored suspension for patients unable to use tablets.

The immediate-release product has the lowest regulatory risk but also the weakest differentiation. The once-daily and sprinkle products have greater commercial upside but require stronger formulation development, more complex clinical bridging, and potentially a 505(b)(2) strategy.

What manufacturing and IP barriers affect a new Zyflo product?

Manufacturing barriers are manageable for immediate-release tablets. They become more significant for extended-release systems because high drug loading can produce large tablets, poor compactability, incomplete release, and sensitivity to process changes.

Key controls include:

• Granulation endpoint.
• Lubrication time.
• Compression force.
• Tablet porosity.
• Polymer distribution.
• Coating weight gain.
• Dissolution profile.
• Moisture exposure.
• Packaging performance.

Geographic patent coverage is likely to be more relevant for a new formulation than for the historical compound. A developer should assess U.S., European, Japanese, and major emerging-market rights separately because formulation patents often have different prosecution outcomes and expiration dates by jurisdiction.

Key Takeaways

• Zyflo is the former branded product for zileuton, a small-molecule 5-lipoxygenase inhibitor.
• Biosimilar risk does not apply.
• The original compound exclusivity period has expired; current barriers are formulation, regulatory, and commercial.
• Immediate-release generic tablets offer the lowest-risk entry but limited differentiation.
• Extended-release, once-daily, sprinkle, and liquid formulations offer the strongest excipient-led opportunities.
• Hypromellose matrix systems, multiparticulate coatings, taste-masking excipients, and suspension platforms are the most relevant technical approaches.
• Hepatic monitoring and competition from once-daily montelukast remain major commercial constraints.
• A conventional generic may fit an ANDA pathway; a materially different dosage form may require 505(b)(2) development.
• Orange Book patent listings and FDA reference-product status must control any paragraph IV or launch analysis.
• The most attractive strategy is a lower-pill-burden formulation with demonstrated control of food effect and dose dumping.

FAQs

Can zileuton be reformulated as a once-daily tablet?

Yes, but a once-daily product would require a high drug load and controlled-release technology capable of maintaining exposure over 24 hours. The regulatory pathway would depend on whether the formulation is sufficiently similar to an approved reference product.

Which excipient is most important for a zileuton extended-release tablet?

Hypromellose is a practical starting polymer for a hydrophilic matrix. Its grade, concentration, hydration behavior, and interaction with tablet porosity will determine the release profile.

Is a liquid zileuton product commercially viable?

It could address dysphagia and pediatric-use segments, but solubility, taste, dose volume, preservative effectiveness, and chemical stability would determine feasibility.

Would an excipient patent block a generic zileuton product?

Only if the relevant patent is enforceable and its claims cover the proposed formulation. A generic developer can often design around narrow excipient claims, but a listed patent may still trigger paragraph IV litigation.

Does Zyflo have a biosimilar market?

No. Zileuton is a chemically synthesized small molecule. Competition proceeds through generic-drug and reformulation pathways rather than the FDA biosimilar pathway.

References

1. U.S. Food and Drug Administration. (n.d.). Zyflo (zileuton) tablets prescribing information. FDA.

2. U.S. Food and Drug Administration. (n.d.). Zyflo CR (zileuton extended-release tablets) prescribing information. FDA.

3. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.

4. U.S. Food and Drug Administration. (2019). Applications covered by section 505(b)(2). FDA.

5. U.S. Food and Drug Administration. (n.d.). Guidance for industry: 180-day exclusivity when multiple ANDA applicants are eligible for paragraph IV certification. FDA.