List of Excipients in Branded Drug PRIMSOL

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	AMMONIUM GLYCYRRHIZATE
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	FRUCTOSE
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	GLYCERIN
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	METHYLPARABEN
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	POVIDONES
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	PROPYLENE GLYCOL
FSC Laboratories Inc	PRIMSOL	trimethoprim hydrochloride	13551-501	PROPYLPARABEN

PRIMSOL Excipient Strategy and Commercial Opportunities

Last updated: August 2, 2026

PRIMSOL is a trimethoprim hydrochloride oral solution containing 50 mg per 5 mL. Its commercial opportunity is driven less by active-ingredient exclusivity than by pediatric dosing, palatability, preservative selection, supply reliability, and the ability to obtain an FDA-approved generic or authorized alternative. The product is a mature small-molecule formulation with no biosimilar pathway and limited apparent patent protection. [1][2]

What is PRIMSOL and what dosage form does it use?

PRIMSOL is an oral liquid formulation of trimethoprim hydrochloride for the treatment of urinary tract infections caused by susceptible organisms. The labeled strength is 50 mg/5 mL, equivalent to 10 mg/mL of trimethoprim. [1]

Product attribute	PRIMSOL
Active ingredient	Trimethoprim hydrochloride
Dosage form	Oral solution
Strength	50 mg/5 mL
Therapeutic category	Antibacterial
Primary use	Susceptible urinary tract infections
FDA pathway	Approved NDA
Biosimilar applicability	None; trimethoprim is a small molecule
Primary commercial users	Pediatric patients, patients unable to swallow tablets, caregivers
Key formulation drivers	Taste, preservative system, dosing accuracy, chemical stability

The oral solution is particularly relevant for children and adults who cannot use tablets. The liquid format also creates formulation and manufacturing barriers that do not apply to conventional trimethoprim tablets.

What excipients are used in PRIMSOL?

The PRIMSOL labeling identifies a conventional aqueous oral-solution excipient system. Public labeling identifies citric acid, edetate disodium, glycerin, methylparaben, propylene glycol, sodium citrate, sucrose, water, and flavoring components among the inactive ingredients. [1]

Excipient category	PRIMSOL excipient or function	Commercial purpose
Sweetener	Sucrose	Reduces bitterness and improves pediatric acceptability
Humectant and solvent	Glycerin	Supports mouthfeel, viscosity, and solubilization
Co-solvent	Propylene glycol	Assists flavor and formulation-component solubilization
Buffer system	Citric acid and sodium citrate	Controls pH and supports chemical stability
Chelating agent	Edetate disodium	Binds trace metals that can accelerate degradation
Preservative	Methylparaben	Controls microbial growth in a multidose bottle
Vehicle	Purified water	Main liquid carrier
Flavor	Proprietary flavor system	Masks trimethoprim bitterness

The excipient strategy is functional rather than differentiated. It addresses the central technical risks of an aqueous pediatric antibiotic: bitterness, microbial contamination, pH control, oxidation or metal-catalyzed degradation, and dosing acceptability.

How strong is the PRIMSOL formulation strategy?

The formulation is commercially practical but not difficult to replicate at the ingredient level. Its defensibility is likely to arise from execution rather than composition-of-matter protection.

Taste masking

Trimethoprim has a pronounced bitter taste. Sucrose, glycerin, propylene glycol, and flavoring are used to improve acceptability. A competing product could seek differentiation through:

• Lower sugar content
• Sugar-free or reduced-sugar formulation
• Improved flavor persistence
• Reduced aftertaste
• Better acceptance among children
• Flavors selected for regional preferences
• Unit-dose packaging that limits repeated exposure to the taste

Taste masking is a meaningful commercial opportunity because pediatric adherence depends on whether a child accepts repeated doses. A formulation that matches PRIMSOL's antimicrobial performance but has better palatability could gain pharmacy and caregiver preference.

pH and chemical stability

The citric acid-sodium citrate system provides pH control. Edetate disodium can reduce the effect of trace-metal impurities on degradation. A reformulated product would need to preserve trimethoprim potency across the proposed shelf life while maintaining preservative efficacy and acceptable taste.

The principal development risks include:

1. Trimethoprim precipitation or reduced solubility during storage.
2. Preservative loss or reduced antimicrobial activity at the selected pH.
3. Interaction between flavor oils and packaging.
4. Color or odor changes caused by oxidation or extractables.
5. Dose nonuniformity after repeated bottle opening.

Preservative system

Methylparaben is a conventional multidose-liquid preservative. A competing product could evaluate alternative systems such as potassium sorbate, sodium benzoate, or combination preservatives, subject to pH compatibility, safety, preservative-effectiveness testing, and FDA acceptance.

A preservative change is not automatically a commercial advantage. It can create regulatory and technical burdens involving:

• Antimicrobial effectiveness testing
• Preservative concentration uniformity
• Pediatric exposure assessment
• Container-closure compatibility
• Stability after opening
• Labeling of inactive ingredients

A preservative-free product would require a different delivery model, such as unit-dose containers or a reconstituted powder. That model could reduce multidose contamination risk but would raise packaging and manufacturing costs.

What formulation improvements could create commercial opportunities?

Sugar-free PRIMSOL alternative

A sugar-free oral solution could target diabetic patients, caregivers seeking lower sugar exposure, and institutional buyers. The primary challenge is replacing sucrose without increasing bitterness or producing an unpleasant mouthfeel.

Potential excipient directions include:

• Sucralose or acesulfame potassium for high-intensity sweetness
• Sorbitol or glycerin for bulk and mouthfeel
• Controlled flavor modulation
• Lower-viscosity systems for easier swallowing

The formulation would need to avoid excessive polyol use, which can cause gastrointestinal effects in sensitive patients.

Alcohol-free formulation

An alcohol-free product may be attractive for pediatric and institutional use. PRIMSOL already relies on an aqueous system with glycerin and propylene glycol rather than ethanol as the principal vehicle. A competing product should therefore focus on minimizing total co-solvent exposure and clearly controlling the amount of propylene glycol.

Improved dosing system

A calibrated oral syringe, bottle adapter, and child-resistant closure can produce practical differentiation. Dosing errors are a recurring risk with oral liquids. Commercial opportunities include:

• Metric-only labeling
• Supplied oral syringe rather than a cup
• Low-residual-volume bottle design
• Tamper-evident unit
• Integrated bottle adapter
• Unit-dose packaging for hospitals and long-term-care facilities

These features may be protected through device or packaging patents even when the drug formulation itself is unpatented.

Ready-to-use versus powder-for-reconstitution

A ready-to-use solution offers convenience and avoids reconstitution errors. A powder-for-reconstitution product could improve shipping stability and reduce transport weight, but it requires validated reconstitution instructions and reliable final concentration.

Product model	Advantages	Principal barriers
Ready-to-use solution	Immediate use, no mixing errors	Higher shipping weight, preservative and stability burden
Powder for reconstitution	Better logistics, potentially longer dry-state stability	Reconstitution accuracy, dose uniformity, caregiver burden
Unit-dose solution	Lower contamination risk, institutional convenience	Higher packaging cost and waste
Concentrated solution	Smaller package, lower shipping volume	Dosing errors and safety concerns
Sugar-free solution	Differentiated pediatric and chronic-use profile	Taste masking and gastrointestinal tolerability

When does PRIMSOL lose exclusivity?

PRIMSOL's active ingredient, trimethoprim, is an old small-molecule antibacterial. The commercial exclusivity associated with the original product has expired. FDA generic competition is legally available through an abbreviated new drug application if a sponsor can demonstrate the required pharmaceutical equivalence, bioequivalence, quality, and labeling compliance. [2][3]

Exclusivity issue	PRIMSOL assessment
New chemical entity exclusivity	Expired
Orphan-drug exclusivity	Not applicable
Biologic exclusivity	Not applicable
Pediatric exclusivity	No current exclusivity identified in the public product record
Orange Book patent barrier	No material current patent barrier identified in the cited FDA records
Generic pathway	ANDA, subject to FDA requirements
Biosimilar pathway	Not applicable

Patent expiration dates for the original trimethoprim molecule are historical and do not provide a current barrier to entry. The relevant commercial question is whether any later formulation, method-of-use, manufacturing, or device patent is listed or enforceable against a proposed product.

What patents protect PRIMSOL?

The commercial protection around PRIMSOL appears limited. The FDA Orange Book is the primary public source for patents and regulatory exclusivities associated with approved drug products. [2]

No material active Orange Book-listed patent protection is identified here for PRIMSOL. That does not eliminate every possible patent issue. A third party could hold patents covering:

• Specific flavor systems
• Sugar-free excipient combinations
• Preservative systems
• Container-closure assemblies
• Dosing devices
• Manufacturing processes
• Stability-enhancing packaging
• Alternative trimethoprim salt forms

Those rights would need separate review through USPTO records, assignment records, prosecution histories, and litigation databases. A generic sponsor should not assume that the absence of an Orange Book listing removes all freedom-to-operate risk.

Method-of-use patents

The labeled use of trimethoprim for susceptible urinary tract infections is old and generally weak as a basis for current exclusivity. A later method-of-use patent could target a narrow patient population, dosing regimen, resistance-management protocol, or combination treatment. Such a patent would have to be assessed against the proposed label and induced-infringement risk.

Formulation patents

Formulation patents would be more commercially relevant than old composition patents. The strongest potential claims would likely require a defined combination of:

• Trimethoprim concentration
• pH range
• Preservative concentration
• Sweetener or flavor system
• Stability profile
• Container-closure configuration

A generic sponsor can reduce risk by using a materially different excipient system, provided the alternative remains pharmaceutically acceptable and bioequivalent where required.

Are Paragraph IV challenges relevant to PRIMSOL?

A Paragraph IV certification is relevant only if an ANDA applicant confronts an unexpired Orange Book-listed patent. If no active listed patent covers PRIMSOL, an ANDA sponsor would generally have no need to rely on Paragraph IV for the core product. The sponsor may instead certify that no patent is listed or make the certification required by the applicable Orange Book status.

Challenge type	Relevance to PRIMSOL
Paragraph I	No patent information listed
Paragraph II	All listed patents expired
Paragraph III	ANDA waits for patent expiration
Paragraph IV	Used only against an unexpired listed patent
Section viii carve-out	Relevant if a patented use is omitted from labeling

The most likely dispute would involve a later-listed formulation or delivery patent, not the historical trimethoprim molecule.

What is the FDA regulatory status of PRIMSOL?

PRIMSOL is an FDA-approved prescription oral solution associated with NDA 019989 in public drug-labeling records. [1] A sponsor seeking to commercialize a competing product would generally evaluate an ANDA strategy rather than a new drug application, assuming the proposed product can meet the applicable equivalence and product-quality requirements. [3]

Key regulatory issues include:

• Same active ingredient and dosage form
• Equivalent strength
• Pharmaceutical equivalence
• Bioequivalence or an FDA-accepted alternative approach
• Matching or permissible labeling
• Product-specific dissolution or in vitro requirements
• Preservative effectiveness
• Microbial limits
• Stability after opening
• Extractables and leachables
• Accurate dosing-device performance

For an oral solution, proving equivalence can differ from proving equivalence for a tablet. The sponsor must control concentration, pH, viscosity, density, preservative content, and dose delivery. FDA guidance on oral solutions and ANDA development should govern the study plan. [3][4]

Which companies are challenging PRIMSOL?

No current high-profile Paragraph IV litigation or publicly established settlement involving PRIMSOL is identified in the cited sources. The likely competitive field consists of generic-drug manufacturers, specialty-liquid manufacturers, and contract development and manufacturing organizations with oral-liquid capacity.

Potential competitor categories include:

1. Established ANDA manufacturers with pediatric-liquid infrastructure.
2. Specialty pharmaceutical companies focused on difficult-to-formulate oral liquids.
3. Contract manufacturers seeking an ANDA sponsor or licensing partner.
4. Branded-generic companies using taste, packaging, or supply reliability as differentiators.

A competitor does not need a stronger patent position than PRIMSOL. It needs reliable FDA approval, competitive manufacturing cost, adequate distribution, and a pharmacy-payor pathway.

What licensing deals affect PRIMSOL?

No current public licensing transaction is identified in the cited FDA label or Orange Book materials. The product's licensing history should be distinguished from current commercial ownership, marketing rights, and manufacturing responsibility. Those functions can be divided among the NDA holder, labeler, contract manufacturer, and distributor.

The most commercially relevant transaction structures would be:

• ANDA acquisition
• Private-label supply agreement
• Authorized-generic arrangement
• Regional marketing license
• Formulation-technology license
• Co-development agreement for sugar-free or unit-dose versions

A licensing deal would have greater value if it included FDA-approved liquid manufacturing capacity, validated stability data, and pharmacy-channel access. The trimethoprim active ingredient itself is widely available and is unlikely to justify a high standalone royalty.

How large is the revenue opportunity?

PRIMSOL is a niche opportunity rather than a high-growth antibiotic platform. Revenue depends on unit volume, reimbursement, shortage conditions, pediatric prescribing, and the availability of competing liquid products.

The most attractive commercial segments are:

• Pediatric urinary tract infection treatment
• Patients with dysphagia
• Long-term-care facilities
• Hospital discharge prescriptions
• Pharmacies needing a reliable oral-liquid supplier
• Markets where liquid trimethoprim products are periodically unavailable

The main revenue risks are low treatment duration, generic-price pressure, substitution by tablets or other antibiotics, antimicrobial stewardship, and limited clinical demand outside the labeled niche.

Generic launch scenarios

Scenario	Market effect	Strategic implication
Single generic entrant	Moderate price pressure	Attractive first-mover economics
Two or more liquid generics	Rapid price compression	Manufacturing cost becomes decisive
Supply disruption	Temporary price and share increase	Inventory and redundancy create value
Sugar-free differentiated product	Premium niche positioning	Requires strong taste and stability data
Unit-dose institutional product	Contract-based revenue	Higher packaging cost but lower dispensing complexity

A first approved generic could capture meaningful share if PRIMSOL has limited direct liquid competition. Long-term returns would decline as additional ANDA approvals enter.

What manufacturing and intellectual-property barriers exist?

The principal barriers are operational and regulatory:

• Validated aqueous-liquid manufacturing
• Microbial control
• Preservative effectiveness
• Stable flavor integration
• Consistent pH and viscosity
• Low-dose filling accuracy
• Packaging compatibility
• Supply of pharmaceutical-grade trimethoprim hydrochloride
• FDA inspection readiness

Geographic coverage depends on the manufacturing site, import controls, registration requirements, and local rules for pediatric medicines. A U.S. ANDA does not automatically create approval in Europe, Canada, Japan, or emerging markets.

The strongest defensible position would combine an FDA-approved product with a differentiated formulation, reliable supply, pediatric-focused packaging, and contractual pharmacy or institutional distribution. A simple copy of the existing sucrose-preserved solution would face limited legal protection and substantial price competition.

How does PRIMSOL compare with trimethoprim tablets?

Attribute	PRIMSOL oral solution	Trimethoprim tablets
Pediatric use	Strong fit	Limited in younger children
Swallowing difficulty	Strong fit	Poor fit
Manufacturing complexity	Higher	Lower
Packaging burden	Higher	Lower
Taste risk	High	Low
Dosing flexibility	High	Lower
Preservative requirement	Often required for multidose use	Generally not required
Generic price pressure	Potentially lower with few liquid entrants	Usually high
Differentiation potential	Taste, device, sugar-free, unit-dose	Limited

Key Takeaways

• PRIMSOL is a 50 mg/5 mL trimethoprim hydrochloride oral solution.
• Its excipient system uses sucrose, glycerin, propylene glycol, citric acid, sodium citrate, edetate disodium, methylparaben, water, and flavoring components.
• The main formulation opportunities are sugar-free taste masking, improved dosing devices, unit-dose packaging, and preservative or stability enhancements.
• Original-drug exclusivity has expired, and the product does not present a conventional biosimilar issue.
• No material active Orange Book patent barrier or current Paragraph IV litigation is identified in the cited FDA records.
• Commercial value depends on liquid-manufacturing capability, supply reliability, pediatric acceptability, and the number of approved competitors.
• A generic sponsor should focus on formulation execution and regulatory readiness rather than historical trimethoprim patent protection.
• The most defensible product would combine FDA approval with differentiated excipients, packaging, and reliable institutional distribution.

FAQs

Is PRIMSOL a generic drug?

PRIMSOL is a branded trimethoprim oral solution. Competing trimethoprim oral solutions may be approved as generic products through the ANDA pathway.

Can PRIMSOL be reformulated without sucrose?

Yes, a sponsor can develop a sugar-free alternative, but it must resolve bitterness, mouthfeel, preservative compatibility, stability, and FDA approval requirements.

Does PRIMSOL have a biosimilar competitor?

No. Trimethoprim is a chemically synthesized small molecule, so competing products use the generic-drug pathway rather than the biosimilar pathway.

What is the most valuable patent opportunity around PRIMSOL?

The strongest potential patent opportunity is likely a narrow formulation, packaging, or dosing-device claim that produces a measurable stability, palatability, contamination-control, or dosing-accuracy benefit.

Is trimethoprim oral solution commercially attractive?

It can be attractive as a niche generic or differentiated pediatric liquid, particularly where direct liquid competition is limited. The opportunity is constrained by short treatment courses, generic pricing, antimicrobial stewardship, and substitution by tablets or alternative antibiotics.

References

1. DailyMed. (n.d.). PRIMSOL- trimethoprim hydrochloride solution: Prescribing information. U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/

2. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/

3. U.S. Food and Drug Administration. (2024). Generic drugs: Questions and answers. https://www.fda.gov/drugs/questions-answers/generic-drugs

4. U.S. Food and Drug Administration. (n.d.). Product-specific guidances for generic drug development. https://www.fda.gov/drugs/drug-compendia/product-specific-guidances-generic-drug-development