List of Excipients in Branded Drug KARBINAL

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Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Aytu Therapeutics LLC	KARBINAL	carbinoxamine maleate	23594-101	ANHYDROUS CITRIC ACID
Aytu Therapeutics LLC	KARBINAL	carbinoxamine maleate	23594-101	GLYCERIN
Aytu Therapeutics LLC	KARBINAL	carbinoxamine maleate	23594-101	HIGH FRUCTOSE CORN SYRUP
Aytu Therapeutics LLC	KARBINAL	carbinoxamine maleate	23594-101	METHYLPARABEN
Aytu Therapeutics LLC	KARBINAL	carbinoxamine maleate	23594-101	POLYSORBATE 80
Aytu Therapeutics LLC	KARBINAL	carbinoxamine maleate	23594-101	POVIDONE

KARBINAL ER Excipient Strategy and Commercial Opportunities

Last updated: October 17, 2026

KARBINAL ER is a prescription extended-release oral suspension containing carbinoxamine maleate at 4 mg per 5 mL. Its commercial differentiation depends on liquid dosing, pediatric usability, palatability, physical stability, and the delivery technology supporting extended release. The main excipient opportunity is not a simple substitution of inactive ingredients. A competing product would need to reproduce dose uniformity, suspension stability, taste, preservative performance, and pharmacokinetic behavior while meeting FDA requirements for an abbreviated new drug application or 505(b)(2) pathway.

What is KARBINAL ER and how is it regulated?

KARBINAL ER is an FDA-approved extended-release oral suspension for relief of symptoms associated with seasonal and perennial allergic rhinitis and vasomotor rhinitis. It contains carbinoxamine maleate, a first-generation H1 antihistamine, at a concentration of 0.8 mg/mL. The labeled dose is administered using a calibrated oral dosing device rather than a household teaspoon. [1]

Attribute	KARBINAL ER
Active ingredient	Carbinoxamine maleate
Dosage form	Extended-release oral suspension
Strength	4 mg per 5 mL
Route	Oral
FDA application	NDA 206156
Applicant	Tris Pharma, Inc.
Initial FDA approval	2013
Primary population	Adults and pediatric patients aged 2 years and older
Therapeutic category	Antihistamine; allergy and rhinitis
Regulatory status	Prescription drug
Biosimilar pathway	Not applicable
Likely competitive pathways	ANDA, 505(b)(2), authorized-generic or reformulated product

KARBINAL ER is not a biologic. Biosimilar competition is therefore irrelevant. Competitive risk comes from generic carbinoxamine products, alternative antihistamines, compounded oral liquids, and new or reformulated liquid allergy products.

What excipients are used in KARBINAL ER?

The FDA prescribing information identifies the following inactive ingredients:

Excipient	Likely functional role
Citric acid, anhydrous	Acidulant and pH adjustment
Edetate disodium	Chelating agent; supports preservative and stability performance
Glycerin	Humectant, solvent, mouthfeel modifier
Methylparaben	Antimicrobial preservative
Propylene glycol	Solvent and cosolvent
Purified water	Continuous phase
Sodium citrate dihydrate	Buffering agent
Sorbitol	Sweetener, bulking agent, viscosity and mouthfeel modifier
Sucralose	High-intensity sweetener
Xanthan gum	Suspending and viscosity-building agent

The label does not treat these ingredients as the source of the extended-release claim. The release profile is more likely to depend on the formulation matrix, particle attributes, viscosity, drug-excipient interactions, and manufacturing process than on any single conventional excipient. [1]

How does the KARBINAL ER excipient system work?

The formulation uses a conventional but commercially effective liquid-suspension architecture.

Suspension and dose uniformity

Xanthan gum increases viscosity and reduces sedimentation. This is essential because the product is a suspension rather than a true solution. The formulation must remain readily redispersible after storage and provide consistent drug delivery throughout the bottle.

The key performance parameters are:

• sedimentation rate;
• ease and speed of redispersion;
• particle-size distribution;
• viscosity at low and high shear;
• delivered dose after standing;
• content uniformity at the beginning, middle, and end of bottle use.

A generic developer cannot rely on nominal composition alone. A formulation with the same xanthan gum concentration may perform differently because of polymer grade, hydration method, shear history, drug particle size, or order of addition.

Taste masking

Carbinoxamine is a first-generation antihistamine with an unfavorable taste profile for pediatric use. KARBINAL ER combines sorbitol, sucralose, glycerin, and propylene glycol to improve palatability and mouthfeel. The acidic citrate system also influences taste and chemical stability.

Taste masking is commercially important because pediatric adherence is directly affected by bitterness, aftertaste, mouth coating, and dosing volume. A replacement product with comparable pharmacokinetics but inferior palatability could lose market share despite a lower price.

Preservation and microbiological control

Methylparaben provides antimicrobial preservation. Edetate disodium can improve preservative effectiveness by binding trace metals that support microbial growth or catalyze oxidation. The acidic environment created by citric acid and sodium citrate may further support chemical and microbiological control.

A preservative change would require a complete preservative-effectiveness and stability package. It could also alter taste, viscosity, packaging compatibility, and regulatory classification of the product.

pH and chemical stability

Citric acid and sodium citrate create a buffered acidic system. The target pH must balance several competing requirements:

• carbinoxamine chemical stability;
• preservative performance;
• taste;
• xanthan gum hydration and viscosity;
• container compatibility;
• tolerability in the oral cavity.

A competitor that changes the buffer system may gain a taste or stability advantage, but the change can affect suspension behavior and release characteristics.

What excipient strategies could compete with KARBINAL ER?

Strategy 1: Develop an equivalent suspension

The lowest-risk approach is to reproduce the established formulation architecture using pharmacopeial-grade excipients. The development program would focus on equivalent quality attributes rather than exact quantitative duplication.

Priority workstreams include:

1. matching carbinoxamine particle size and polymorphic form;
2. optimizing xanthan gum grade and concentration;
3. confirming preservative effectiveness;
4. reproducing pH, viscosity, redispersibility, and sedimentation;
5. demonstrating dose uniformity through the labeled shelf life;
6. conducting comparative pharmacokinetic studies.

This route is most compatible with an ANDA if the product can demonstrate pharmaceutical equivalence and bioequivalence. [2]

Strategy 2: Use a non-sugar pediatric formulation

Sorbitol provides sweetness and body but can cause gastrointestinal discomfort at sufficiently high exposure. A competitor could investigate a lower-sorbitol or sorbitol-free composition using glycerin, maltitol, mannitol, or a combination of high-intensity sweeteners.

Commercial advantages could include:

• lower sugar alcohol burden;
• differentiated pediatric positioning;
• improved suitability for certain patients;
• potential reduction in gastrointestinal complaints.

The risks include altered viscosity, weaker mouthfeel, new taste-masking requirements, and a need to establish equivalence.

Strategy 3: Replace methylparaben

Parabens remain accepted pharmaceutical preservatives, but some customers and caregivers prefer paraben-free products. Possible alternatives include potassium sorbate, sodium benzoate, or phenoxyethanol, subject to pH and regulatory suitability.

A paraben-free formulation could support premium pricing or pharmacy substitution where caregiver preference affects product selection. The principal technical risks are inadequate antimicrobial coverage, altered taste, incompatibility with packaging, and loss of stability.

Strategy 4: Improve suspension technology

A competitor could use a different suspending system, such as a combination of microcrystalline cellulose and carboxymethylcellulose, poloxamer-based systems, or a modified cellulose polymer.

Potential benefits include:

• improved redispersibility;
• lower viscosity during pouring;
• reduced sedimentation;
• better dose recovery from the bottle;
• improved manufacturing robustness.

The critical issue is release comparability. Changes in viscosity, wetting, particle coating, or polymer adsorption may change drug release and gastrointestinal exposure.

Strategy 5: Develop a ready-to-use or unit-dose presentation

KARBINAL ER is supplied as a multidose oral suspension. Commercially differentiated formats could include:

• unit-dose cups;
• stick packs;
• sachets;
• premeasured oral syringes;
• smaller-volume bottles for travel or school use.

Packaging innovation can reduce dosing errors and improve adherence. It may also create a 505(b)(2) opportunity if the product changes delivery or dosing convenience without relying on an exact generic formulation.

What formulation patents may protect KARBINAL ER?

The commercial protection for KARBINAL ER may extend beyond the active ingredient. Relevant protection can include:

• extended-release oral liquid formulations;
• suspension systems;
• drug-release control through excipient matrices;
• particle-size or processing limitations;
• dosage regimens;
• pediatric administration;
• manufacturing processes;
• container-closure systems.

The FDA label identifies KARBINAL ER as an extended-release formulation but does not establish the complete scope of any patent claims. Patent status must be reviewed through the current FDA Orange Book, USPTO records, and applicable district-court or Patent Trial and Appeal Board records. [1, 3, 4]

A freedom-to-operate review should separate three questions:

Question	Commercial relevance
Is carbinoxamine itself patent-protected?	Determines active-ingredient entry risk
Are extended-release liquid formulations protected?	Determines formulation and ANDA litigation risk
Are specific excipient combinations or manufacturing steps claimed?	Determines design-around options

Exact excipient substitution does not automatically avoid infringement. A patent claim may cover functional limitations, concentration ranges, viscosity parameters, release profiles, or a combination of components rather than a single named ingredient.

When does KARBINAL ER lose exclusivity?

KARBINAL ER’s market exclusivity is determined by the intersection of FDA regulatory exclusivity and patent rights. Its 2013 approval is too old for ordinary five-year new chemical entity exclusivity to remain active. Any current barrier is therefore more likely to involve listed patents, formulation claims, regulatory exclusivity tied to a later innovation, or commercial execution.

Protection type	Relevance to KARBINAL ER
New chemical entity exclusivity	Historical five-year period; no longer active
Three-year clinical-investigation exclusivity	Depends on qualifying later approval
Pediatric exclusivity	Could add six months if granted for a qualifying study
Orphan exclusivity	Not expected for allergic rhinitis
Listed patents	Must be confirmed in the current Orange Book
Trade secrets	May cover process controls, excipient grades, and manufacturing parameters

The practical generic-entry date cannot be determined from the approval date alone. It depends on listed patent expiration, patent-term adjustment, pediatric extensions, Paragraph IV litigation, settlement terms, and FDA approval timing.

What Paragraph IV risks exist for KARBINAL ER?

A generic applicant could file a Paragraph IV certification against a listed patent by asserting that the patent is invalid, unenforceable, or not infringed. The reference-product sponsor could then bring patent litigation, triggering the potential 30-month stay under the Hatch-Waxman framework. [2]

The most likely technical dispute areas are:

• whether the proposed suspension has the claimed extended-release characteristics;
• whether the proposed viscosity or polymer system falls within claim scope;
• whether the generic formulation uses a claimed excipient combination;
• whether process limitations are met;
• whether the generic product is bioequivalent despite formulation changes.

For a small-market liquid product, litigation economics can differ from those for high-revenue tablets. A generic company may prefer a narrow design-around, authorized generic arrangement, or 505(b)(2) product rather than prolonged litigation.

Which companies could challenge or compete with KARBINAL ER?

The competitive field includes several groups:

1. Generic manufacturers with oral-liquid infrastructure, including companies active in pediatric suspensions.
2. Sponsors of carbinoxamine tablets or immediate-release oral liquids.
3. Manufacturers of alternative antihistamines such as cetirizine, loratadine, levocetirizine, and desloratadine.
4. Compounding pharmacies producing extemporaneous carbinoxamine liquids where legally permitted.
5. Specialty pharmaceutical companies acquiring or licensing pediatric delivery technologies.

The strongest competitive threat is a product that combines carbinoxamine with lower dosing friction, better taste, lower preservative burden, and reliable supply.

What are the commercial opportunities in KARBINAL ER excipients?

Premium pediatric reformulation

A reformulated carbinoxamine suspension could target caregivers seeking better taste, fewer excipients of concern, lower sugar-alcohol content, or easier dosing. The value proposition would be strongest if supported by taste-testing data and a smaller or more convenient dose volume.

Authorized generic supply

An authorized generic could capture price-sensitive prescriptions while preserving brand participation in the category. This strategy is most attractive if the product has meaningful pharmacy demand but insufficient volume to support multiple independent generic entrants.

Excipient licensing

A formulation owner could license:

• taste-masking technology;
• low-sedimentation suspension systems;
• preservative-free multidose packaging;
• unit-dose pediatric delivery;
• controlled-release liquid platforms.

Licensing value would depend on freedom to operate, FDA precedent, manufacturing scalability, and whether the technology can be reused across other antihistamines or pediatric drugs.

Contract manufacturing

KARBINAL ER-type products require specialized liquid manufacturing, including controlled hydration of polymers, high-shear dispersion, suspension homogenization, filling, and microbial controls. Contract manufacturers with these capabilities can pursue generic, private-label, and 505(b)(2) opportunities.

Geographic expansion

The U.S. formulation may not transfer directly to every market. Regional opportunities depend on:

• local acceptance of methylparaben and propylene glycol;
• pediatric excipient restrictions;
• availability of food-grade flavors and sweeteners;
• local preservative rules;
• registration requirements for extended-release liquids;
• cold-chain or packaging conditions.

The same excipient platform could support non-U.S. allergy products, but local formulation and stability work would be required.

How strong is the KARBINAL ER formulation strategy?

KARBINAL ER has a commercially coherent excipient system: xanthan gum supports suspension, citrate controls pH, methylparaben supports preservation, and multiple polyols and sweeteners address pediatric palatability. Its defensibility is likely stronger at the formulation-process level than at the level of individual excipients.

The main barriers for a competitor are development execution and regulatory proof:

• maintaining dose uniformity over bottle use;
• matching extended-release performance;
• achieving acceptable taste;
• meeting preservative and microbial limits;
• avoiding formulation and process patent claims;
• demonstrating bioequivalence with a liquid suspension.

No single excipient is likely to create a durable moat. The commercial opportunity lies in an integrated platform that improves palatability, dosing accuracy, stability, and manufacturing economics.

Key Takeaways

• KARBINAL ER is a 4 mg/5 mL extended-release carbinoxamine maleate oral suspension approved under NDA 206156.
• Its core excipient system includes xanthan gum, methylparaben, citrate buffer, glycerin, propylene glycol, sorbitol, sucralose, edetate disodium, and purified water.
• The main technical barrier is reproducing the complete performance profile, not copying one excipient.
• The most credible commercial opportunities are pediatric taste improvement, paraben-free or lower-polyol formulations, unit-dose packaging, authorized generics, and licensed suspension technology.
• KARBINAL ER has no biosimilar risk because carbinoxamine is a small-molecule drug.
• Generic risk depends on current Orange Book listings, patent claims, Paragraph IV activity, litigation, and settlement terms.
• A formulation patent may cover functional attributes, release behavior, concentration ranges, or manufacturing steps even when individual excipients are conventional.
• Product-level revenue and market-share decisions require current prescription and sales data; the FDA label does not disclose commercial performance.

FAQs

Can KARBINAL ER be reformulated without xanthan gum?

Yes. A competing product could use cellulose polymers, microcrystalline cellulose systems, carbomers, or other suspending agents. The replacement must preserve redispersibility, dose uniformity, viscosity, stability, and bioequivalence.

Is methylparaben essential to KARBINAL ER?

No. Methylparaben is a labeled preservative, but another preservative system could be evaluated. Any change would require preservative-effectiveness, stability, taste, packaging, and regulatory assessment.

Does sorbitol make KARBINAL ER unsuitable for children?

No. Sorbitol is used as a sweetener and bulking agent, but gastrointestinal tolerance depends on dose and patient sensitivity. A lower-sorbitol formulation could be commercially differentiated.

Could a carbinoxamine tablet generic replace KARBINAL ER?

Not automatically. A tablet has a different dosage form, dosing pattern, excipient system, and potentially different release characteristics. Substitution depends on state law, prescriber authorization, pharmacy practice, and product-specific FDA approval.

What is the strongest design-around opportunity for KARBINAL ER?

A unit-dose, better-tasting suspension using a differentiated suspending system and preservative strategy is the clearest design-around concept. Its commercial value would depend on avoiding active formulation claims while demonstrating equivalent or superior clinical performance.

References

1. U.S. Food and Drug Administration. (2024). KARBINAL ER (carbinoxamine maleate) extended-release oral suspension: Prescribing information.
2. U.S. Food and Drug Administration. (n.d.). Abbreviated new drug application process and generic drug approval requirements.
3. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book.
4. United States Patent and Trademark Office. (n.d.). Patent Center and patent term information.