List of Excipients in Branded Drug CHLORZOXAZONE

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Generic Drugs Containing CHLORZOXAZONE

Company	Ingredient	NDC	Excipient
Endo USA Inc	chlorzoxazone	0254-2005	ANHYDROUS LACTOSE
Endo USA Inc	chlorzoxazone	0254-2005	CELLULOSE, MICROCRYSTALLINE
Endo USA Inc	chlorzoxazone	0254-2005	CROSCARMELLOSE SODIUM
Endo USA Inc	chlorzoxazone	0254-2005	DOCUSATE SODIUM/SODIUM BENZOATE
Endo USA Inc	chlorzoxazone	0254-2005	MAGNESIUM STEARATE
Endo USA Inc	chlorzoxazone	0254-2005	STARCH, CORN

What are the Most Frequently-Used Excipients in CHLORZOXAZONE?

# Of NDCs	Excipient
4	ALCOHOL
1	ALUMINUM OXIDE
17	ANHYDROUS LACTOSE
57	CELLULOSE, MICROCRYSTALLINE
31	CROSCARMELLOSE SODIUM
6	D&C RED NO. 27

Chlorzoxazone Excipient Strategy and Commercial Opportunities

Last updated: October 1, 2026

Chlorzoxazone is a mature, multisource oral muscle relaxant with limited active-ingredient patent protection and low barriers to conventional generic entry. Commercial value is concentrated in formulation differentiation, combination products, patient-friendly dosage forms, contract manufacturing, and geographic markets where supply reliability or dosage-form upgrades remain limited.

The strongest near-term opportunity is an improved immediate-release oral product using a robust excipient system for rapid disintegration, content uniformity, stability, and lower manufacturing cost. More differentiated opportunities include orally disintegrating tablets, oral suspensions, unit-dose sachets, and fixed-dose combinations with analgesics. The primary clinical limitation is chlorzoxazone-associated hepatotoxicity, which excipients cannot eliminate and which constrains premium positioning. [1,2]

What is chlorzoxazone and how is it commercially positioned?

Chlorzoxazone is a centrally acting skeletal muscle relaxant used with rest, physical therapy, and other measures for painful musculoskeletal conditions. In the United States, the drug is marketed primarily as an oral generic tablet in 250 mg and 500 mg strengths. Parafon Forte DSC, historically associated with chlorzoxazone, is no longer the principal commercial brand opportunity in the U.S. market. [3,4]

Attribute	Commercial assessment
Active ingredient	Chlorzoxazone
Drug class	Centrally acting skeletal muscle relaxant
Common dosage form	Immediate-release oral tablet
Common strengths	250 mg and 500 mg
U.S. regulatory status	Generic prescription drug; ANDA-based competition
Primary therapeutic use	Acute painful musculoskeletal conditions
Biologic status	Not applicable
Biosimilar pathway	Not applicable
Core commercial risk	Hepatotoxicity, sedation, mature generic competition
Main differentiation route	Formulation, packaging, combination products, geographic supply

Chlorzoxazone is not a biologic and does not create biosimilar exposure. Commercial competition comes from generic drug manufacturers, branded generic companies, regional pharmaceutical suppliers, and combination-product manufacturers.

What excipients are suitable for chlorzoxazone tablets?

A conventional immediate-release tablet should prioritize rapid disintegration, acceptable dissolution, low tablet weight, and manufacturing robustness. The excipient selection depends on the active pharmaceutical ingredient’s particle size, flow, compressibility, polymorphic form, and dissolution behavior.

Recommended excipient architecture

Formulation function	Candidate excipients	Commercial rationale
Diluent	Microcrystalline cellulose, lactose monohydrate, dibasic calcium phosphate	Supports tablet weight, flow, and compression
Superdisintegrant	Croscarmellose sodium, crospovidone, sodium starch glycolate	Improves breakup and dissolution
Binder	Povidone, copovidone, pregelatinized starch, hydroxypropyl cellulose	Supports granule strength and tablet integrity
Lubricant	Magnesium stearate, sodium stearyl fumarate	Reduces ejection force and sticking
Glidant	Colloidal silicon dioxide	Improves powder flow
Wetting agent	Sodium lauryl sulfate or poloxamer, where justified	May improve wetting of poorly water-soluble drug particles
Film coating	Hypromellose, polyvinyl alcohol, polyethylene glycol, titanium dioxide or permitted colorants	Improves swallowability, appearance, and moisture protection
Taste modifier	Sweeteners, flavors, ion-exchange resins, polymeric coating	Relevant to liquid and orally disintegrating products

A direct-compression formula is commercially attractive because it reduces process steps and equipment requirements. It may be unsuitable if chlorzoxazone has poor flow, segregation risk, low compressibility, or dissolution dependence on particle size. A wet-granulation process can improve content uniformity and tablet strength but increases manufacturing cost and exposes the drug to water and drying conditions.

The preferred development sequence is:

1. Characterize API particle size, bulk density, flow, moisture sensitivity, and dissolution.
2. Screen direct compression with microcrystalline cellulose and a superdisintegrant.
3. Compare wet granulation if flow or content uniformity is inadequate.
4. Optimize lubricant concentration and blending time to avoid dissolution slowdown.
5. Confirm dissolution against the reference product or applicable compendial target.
6. Assess extractables, impurities, and stability under accelerated conditions.

Which excipient risks matter most?

Magnesium stearate can reduce wetting and slow dissolution when used at excessive concentrations or blended for too long. Hydrophobic coating systems can create a similar risk. Sodium lauryl sulfate may improve wetting but can affect tolerability and should be justified through dissolution and stability data.

Lactose-based systems may be unsuitable for patients with lactose intolerance or for manufacturers seeking a lactose-free product. Mannitol can improve mouthfeel in orally disintegrating tablets but increases cost and may require moisture-control measures. Crospovidone is often useful where rapid disintegration and low gelling risk are priorities. Sodium starch glycolate can provide strong swelling but requires control of concentration and granule structure.

What formulation strategies offer commercial differentiation?

Immediate-release tablets

The immediate-release tablet remains the lowest-risk opportunity. A differentiated product can compete through:

• Lower tablet weight
• Improved swallowability
• Faster disintegration
• Scored 500 mg tablets
• Color-coded strength identification
• Moisture-protective packaging
• Consistent supply to hospitals and retail pharmacies
• Latex-free and gluten-free positioning where supported by the full formulation

This approach is unlikely to support strong premium pricing in the U.S. unless it solves a documented manufacturing, supply, adherence, or procurement problem.

Orally disintegrating tablets

An orally disintegrating tablet could target patients who have difficulty swallowing conventional tablets. Mannitol, crospovidone, low-substituted hydroxypropyl cellulose, and suitable flavor systems are potential components.

The principal technical problems are chlorzoxazone’s dose burden, bitter taste, tablet friability, and the need to control moisture. Taste masking may require polymer coating, complexation, or a multiparticulate approach. A 500 mg orally disintegrating product may be difficult to commercialize as a single compact tablet without excessive size or poor mechanical strength. A 250 mg strength, divided-dose regimen, or orally disintegrating granule may be more practical.

An ODT can support a 505(b)(2) strategy only if the regulatory pathway and clinical or bioavailability claims justify it. A conventional generic ODT may still require an ANDA if the product can meet sameness and bioequivalence requirements.

Oral suspension

A chlorzoxazone suspension could address pediatric, geriatric, dysphagic, and institutional-use segments. The formulation would require:

• Suspending agent
• Wetting agent
• Buffer system
• Preservative or validated preservative-free packaging
• Sweetener and flavor
• Sedimentation control
• Redispersibility testing
• Dose-delivery device validation

Potential suspending systems include microcrystalline cellulose and carboxymethylcellulose combinations, xanthan gum, or other pharmaceutically accepted polymers. The development challenge is not only physical stability. Chlorzoxazone’s taste, dose volume, chemical stability, microbial control, and uniform dosing must be addressed.

A ready-to-use suspension could have stronger differentiation than another tablet, particularly in markets with limited liquid muscle-relaxant supply. Unit-dose cups or oral syringes may improve institutional use.

Fixed-dose combinations

Chlorzoxazone has commercial relevance in combination products with analgesics, especially acetaminophen. Combination products may improve adherence and simplify prescribing, but they also increase regulatory and safety complexity.

A chlorzoxazone-acetaminophen product must account for:

• Total daily acetaminophen exposure
• Hepatic risk from both the active drug and acetaminophen
• Dose proportionality
• Potential differences in dissolution
• Labeling for sedation and driving impairment
• Combination-product approval requirements
• Market restrictions in jurisdictions with concern over analgesic toxicity

The commercial case is stronger where physicians and pharmacies already use the combination. It is weaker where regulators or payers prefer separate titration of the muscle relaxant and analgesic.

What patents protect chlorzoxazone products?

The original composition-of-matter and early product protection for chlorzoxazone expired many years ago. The active ingredient is a mature generic molecule, and the principal U.S. commercial products do not depend on an active, enforceable compound patent.

Current intellectual-property value is more likely to arise from:

• Specific modified-release systems
• Taste-masked multiparticulates
• ODT architecture
• Stabilized liquid formulations
• Novel suspension systems
• Unit-dose packaging
• Combination products
• Manufacturing processes
• Specific impurity-control methods

These rights would protect only the claimed formulation, process, or use. They would not prevent competitors from selling ordinary immediate-release chlorzoxazone tablets.

IP category	Likely status and value
Chlorzoxazone compound patent	Expired
Conventional 250 mg or 500 mg tablet	Generally weak patent position
Immediate-release excipient combination	Potentially patentable but difficult to make broad
ODT formulation	Moderate opportunity if taste masking and performance are distinctive
Oral suspension	Potential opportunity if stability and dosing claims are defensible
Combination with acetaminophen	Potential method, formulation, or regulatory exclusivity opportunity
Manufacturing process	Narrower protection; useful against direct process copying
Packaging and device system	Potentially protectable, usually limited scope

When does chlorzoxazone lose exclusivity?

Chlorzoxazone has already lost primary U.S. market exclusivity. Conventional generic entry is therefore legally available, subject to FDA approval, manufacturing compliance, and product-specific bioequivalence requirements. The FDA Orange Book is the principal source for current patent and exclusivity information for approved drug products. [5]

A sponsor developing a new chlorzoxazone dosage form may pursue one of three broad routes:

1. An ANDA for a therapeutically equivalent generic product.
2. A 505(b)(2) application for a materially different dosage form, formulation, route, or clinical use.
3. A new-drug application supported by original clinical and formulation data, where the proposed product has meaningful clinical differentiation.

Regulatory exclusivity may be available for an eligible new drug application or qualifying modification, but exclusivity would attach to the approved innovation rather than revive protection for chlorzoxazone itself. [6]

What is the Orange Book status of chlorzoxazone?

The relevant U.S. products are generic prescription products rather than a currently dominant patented brand. Orange Book review should focus on the specific reference-listed drug, dosage form, strength, therapeutic-equivalence rating, and any listed patents or exclusivity entries. Generic manufacturers normally compete through ANDAs referencing the applicable listed product. [5]

For a conventional chlorzoxazone tablet, the commercial value of an Orange Book listing is limited because the product is already exposed to multiple generic competitors. A differentiated liquid, ODT, or combination product may not have the same reference-product structure and may require a different regulatory strategy.

Are there Paragraph IV challenges or litigation risks?

Paragraph IV litigation is a realistic feature of generic pharmaceutical development, but chlorzoxazone’s old compound protection does not create the type of high-value patent dispute associated with newer branded drugs. Any Paragraph IV risk would more likely concern a later formulation patent, combination patent, or method-of-use patent.

Potential litigation triggers include:

• A formulation patent listed for a newer chlorzoxazone product
• A patent covering an ODT or taste-masking system
• A combination-product patent
• A manufacturing patent with commercially important process limitations
• A patent-holder suit after an ANDA Paragraph IV notice

For ordinary chlorzoxazone tablets, the larger risks are regulatory deficiency, bioequivalence failure, manufacturing observations, supply disruption, and price erosion. A sponsor should not assume that a novel excipient combination creates meaningful blocking protection. Patentability requires novelty, non-obviousness, written description, enablement, and claim scope that can be enforced against competing products. [7]

How strong is the chlorzoxazone patent estate?

The estate is weak for conventional products and potentially moderate for a narrowly defined differentiated formulation.

Factor	Assessment
Compound protection	Low
Conventional tablet protection	Low
Formulation patent opportunity	Moderate but narrow
Process protection	Moderate if process-specific and difficult to design around
Method-of-use protection	Limited unless a new, supportable indication is established
Regulatory exclusivity	Product-specific and dependent on application type
Litigation leverage	Low for standard tablets; higher for a differentiated platform
Freedom-to-operate complexity	Generally manageable for ordinary generic tablets

A sponsor should value chlorzoxazone formulation patents as defensive or niche assets rather than as broad market-exclusion tools.

What commercial opportunities exist by dosage form and region?

U.S. market

The U.S. market favors low-cost generic tablets. Opportunities include contract manufacturing, hospital supply, private-label products, and differentiated products for dysphagia. Premium pricing for a standard tablet is difficult without a documented supply or patient-use advantage.

Emerging and international markets

Commercial opportunities may be stronger in markets where:

• Chlorzoxazone is widely prescribed but liquid products are scarce.
• Local manufacturers have limited formulation capability.
• Hospital procurement rewards reliable supply.
• Combination products are common.
• Pharmacies require locally packaged or unit-dose products.
• Regulatory agencies permit streamlined registration of established products.

Geographic expansion requires country-specific assessment of registered strengths, prescription status, combination-product rules, excipient acceptability, stability zones, packaging requirements, and local patent status. A formulation that is commercially differentiated in one country may be an ordinary generic in another.

Licensing and partnership opportunities

Licensing value is most plausible in four structures:

1. A regional license for an oral suspension or ODT.
2. A supply agreement with a hospital-focused generic company.
3. A co-development agreement for a chlorzoxazone-analgesic combination.
4. A technology license for taste masking, granulation, or moisture-protective packaging.

The strongest partner profile is a company with an established regulatory platform, local distribution, and a product portfolio in pain, musculoskeletal medicine, or hospital generics. The asset should be evaluated on regulatory pathway, expected price erosion, manufacturing yield, stability data, and freedom to operate.

What manufacturing and IP barriers affect chlorzoxazone products?

Manufacturing barriers are moderate for tablets and higher for liquids and taste-masked products.

Tablet barriers

• API flow and segregation
• Dissolution sensitivity to lubrication
• Tablet capping or lamination
• Coating uniformity
• Moisture stability
• Cleaning validation for colored or potent formulations
• Low-margin economics at commercial scale

Liquid barriers

• Sedimentation and redispersibility
• Preservative effectiveness
• Chemical degradation
• Taste masking
• Dose uniformity throughout shelf life
• Packaging compatibility
• Distribution under variable temperature conditions

IP barriers

The main IP risk is inadvertent overlap with third-party excipient, taste-masking, controlled-release, device, or combination-product patents. A freedom-to-operate review should cover active U.S. and foreign families, pending applications, formulation claims, process claims, and patents assigned to specialty pharmaceutical companies.

What is the generic launch risk for chlorzoxazone?

For a standard immediate-release tablet, generic launch risk is high because entry barriers are low and competition can rapidly compress price. For a suspension or ODT, development risk increases, but competitive density may fall.

Product concept	Development risk	Differentiation	Pricing outlook
250 mg immediate-release tablet	Low	Low	Low
500 mg immediate-release tablet	Low	Low	Low
Scored or swallow-optimized tablet	Low to moderate	Low to moderate	Low to moderate
ODT	Moderate	Moderate	Moderate
Oral suspension	Moderate to high	Moderate to high	Moderate
Acetaminophen combination	Moderate	Moderate	Market-dependent
Modified-release product	High	Potentially high	Uncertain
Unit-dose institutional product	Moderate	Moderate	Contract-dependent

The most defensible commercial strategy is usually a low-cost tablet platform combined with one differentiated dosage form, rather than investment in a single premium formulation.

What is the revenue exposure from chlorzoxazone?

Public revenue data for chlorzoxazone are fragmented because the product is sold by multiple generic manufacturers and private-label suppliers. No single branded product has the market control associated with a protected innovative medicine. Revenue exposure is therefore distributed across:

• Generic tablet sales
• Combination products
• Institutional contracts
• Regional brands
• Private-label distributors
• Export markets

A sponsor should model revenue using prescription volume, average net selling price, competitor count, tender awards, manufacturing cost, and expected price erosion. Patent expiry is not the main revenue event because the molecule is already off-patent. Supply reliability, formulation availability, and channel access are more important commercial variables.

Key Takeaways

• Chlorzoxazone is a mature generic muscle relaxant with no meaningful compound-patent barrier for ordinary tablets.
• Immediate-release tablets offer the lowest development risk but limited pricing power.
• ODTs and oral suspensions provide stronger differentiation, with higher taste, stability, and regulatory risk.
• Acetaminophen combinations may offer commercial value but increase hepatic-safety and regulatory complexity.
• Excipients should be selected around dissolution, disintegration, flow, taste masking, moisture control, and manufacturability.
• Hepatotoxicity is a core product limitation that excipient innovation cannot remove.
• Formulation and process patents may protect a differentiated product, but they are unlikely to block ordinary chlorzoxazone generics.
• U.S. revenue opportunity is primarily generic, institutional, and supply-driven.
• International opportunities may be stronger where liquid dosage forms, combination products, or reliable local supply are limited.
• The best commercial portfolio is a low-cost tablet plus one differentiated dosage form supported by regional licensing or institutional distribution.

FAQs

Can chlorzoxazone be formulated as a pediatric oral liquid?

Yes. An oral suspension is technically feasible, but taste masking, redispersibility, preservative effectiveness, dose uniformity, and chemical stability require substantial development work.

Is an orally disintegrating chlorzoxazone tablet commercially attractive?

It can be attractive for dysphagic and geriatric patients, but the 250 mg and 500 mg dose burden creates tablet-size, friability, and taste-masking challenges.

Can a new chlorzoxazone excipient combination receive patent protection?

Potentially. Protection would depend on a novel and non-obvious formulation, measurable performance advantages, adequate disclosure, and claims that competitors cannot easily design around.

Does chlorzoxazone have biosimilar competition?

No. Chlorzoxazone is a small-molecule drug, so competition occurs through generic drug pathways rather than biosimilar applications.

Is a chlorzoxazone-acetaminophen product a strong licensing asset?

It can be a regional or channel-specific asset, particularly where combination prescribing is established. Its value is reduced by hepatic-safety concerns, low-cost generic competition, and the need to manage acetaminophen exposure.

References

1. National Library of Medicine. (2024). Chlorzoxazone. DailyMed. https://dailymed.nlm.nih.gov/
2. National Institute of Diabetes and Digestive and Kidney Diseases. (2024). Chlorzoxazone. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. https://www.ncbi.nlm.nih.gov/books/NBK548137/
3. U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs. https://www.accessdata.fda.gov/scripts/cder/daf/
4. National Library of Medicine. (2024). Chlorzoxazone drug label information. DailyMed. https://dailymed.nlm.nih.gov/
5. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
6. U.S. Food and Drug Administration. (2024). New drug application and abbreviated new drug application regulations. https://www.fda.gov/drugs
7. World Intellectual Property Organization. (2024). Patent cooperation treaty and patent examination resources. https://www.wipo.int/ >