List of Excipients in Branded Drug PROQUIN

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Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Depomed Inc	PROQUIN	ciprofloxacin hydrochloride	13913-001	MAGNESIUM STEARATE
Depomed Inc	PROQUIN	ciprofloxacin hydrochloride	13913-001	POLYETHYLENE GLYCOL
Depomed Inc	PROQUIN	ciprofloxacin hydrochloride	13913-001	POVIDONE

PROQUIN XR Excipient Strategy and Commercial Opportunities

Last updated: October 8, 2026

PROQUIN XR is a once-daily, 500 mg extended-release ciprofloxacin hydrochloride tablet developed for uncomplicated urinary tract infections. Its commercial value is tied less to the ciprofloxacin molecule, which is generic, than to controlled-release performance, tablet robustness, bioequivalence, manufacturing cost, and differentiated delivery. The strongest opportunities are generic or reformulated ciprofloxacin extended-release products using robust hydrophilic matrix technology, lower-cost excipient systems, and improved adherence or tolerability.

What is PROQUIN XR and how does its formulation work?

PROQUIN XR contains ciprofloxacin hydrochloride equivalent to 500 mg of ciprofloxacin. The product was approved by the U.S. Food and Drug Administration under NDA 21-473 for once-daily treatment of uncomplicated urinary tract infections in adults. The labeled regimen was one 500 mg tablet once daily for three days.[1]

The product uses an extended-release tablet architecture rather than immediate-release ciprofloxacin dosing. The excipient system must control hydration, gel formation, drug diffusion, tablet erosion, and mechanical integrity over the intended release period.

The FDA-listed inactive ingredients include:

Excipient	Likely formulation function
Hypromellose	Hydrophilic matrix former and release-rate controller
Microcrystalline cellulose	Diluent, compressibility aid, tablet-strength contributor
Crospovidone	Disintegrant or pore-forming component, depending on formulation location and grade
Magnesium stearate	Lubricant
Sodium stearyl fumarate	Alternative or supplemental lubricant
Colloidal silicon dioxide	Glidant and powder-flow aid
Polyethylene glycol	Film-coating plasticizer or coating-process aid
Titanium dioxide	Opacifier and colorant
Carnauba wax	Coating or polishing agent

The exact quantities, grades, particle-size distributions, manufacturing sequence, and coating parameters are not disclosed in the commercial label. Those variables can materially affect dissolution and bioequivalence even when the qualitative ingredient list is similar.

What excipients are most important in PROQUIN XR?

Hypromellose is the principal release-controlling excipient

Hypromellose, also known as hydroxypropyl methylcellulose or HPMC, is the central excipient opportunity in a PROQUIN XR-type product. A hydrophilic HPMC matrix hydrates after ingestion and forms a gel barrier around the ciprofloxacin particles. Drug release is governed by the interaction of:

• HPMC viscosity grade
• Polymer concentration
• Tablet porosity
• Compression force
• Drug loading
• Particle-size distribution
• Dissolution-medium composition
• Gastrointestinal transit conditions

Higher-viscosity HPMC generally produces a stronger gel and slower drug release, but the relationship is not linear. Excessive polymer concentration can reduce drug availability or produce an overly slow release profile. A lower-viscosity grade can improve manufacturability and release consistency but may increase sensitivity to agitation and ionic strength.

A commercial developer should screen multiple HPMC grades rather than treat HPMC as a single interchangeable material. Supplier changes can create a bioequivalence risk if the replacement grade has a different substitution pattern, viscosity profile, particle morphology, or hydration behavior.

Microcrystalline cellulose supports tablet manufacturing

Microcrystalline cellulose is likely to support direct compression, tablet hardness, and content uniformity. It can also influence matrix porosity and liquid penetration. A formulation with inadequate microcrystalline cellulose may show poor tablet strength, edge chipping, or increased friability. Excessive use can accelerate liquid ingress and alter ciprofloxacin release.

The commercial opportunity is to optimize the balance between HPMC and microcrystalline cellulose rather than simply minimize excipient cost. A low-cost matrix that fails dissolution similarity has no practical value.

Lubricants require careful selection

The presence of magnesium stearate and sodium stearyl fumarate creates a formulation-development question. Magnesium stearate is effective but can produce hydrophobic coating of powder particles if overmixed. That effect can reduce tablet wettability, slow dissolution, and increase batch-to-batch variability.

Sodium stearyl fumarate is often used where developers seek lower hydrophobicity or a different lubrication profile. A reformulation that substitutes one lubricant for another may be commercially attractive, but the change must be evaluated against:

• Blend uniformity
• Ejection force
• Tablet tensile strength
• Dissolution at multiple pH levels
• Stability under high humidity
• Bioequivalence performance

Lubricant addition time and mixing intensity can be as important as lubricant identity.

What formulation strategy is most commercially attractive?

The most defensible strategy is a hydrophilic matrix tablet with a limited number of excipients and a release profile that is insensitive to routine manufacturing variation.

A practical development framework is:

Development variable	Commercial objective
HPMC grade and loading	Establish the release-rate window
Microcrystalline cellulose level	Improve compression without accelerating release
Lubricant type and level	Reduce sticking and ejection force without excessive hydrophobicity
Crospovidone location	Control pore formation and tablet breakup
Tablet hardness	Protect handling performance while maintaining dissolution
Film-coat weight	Improve swallowability and appearance without changing release
Manufacturing process	Reduce scale-up and supplier-change risk
Packaging	Limit moisture-related release drift

A matrix tablet may be preferable to a more complex osmotic or multiparticulate system because it can reduce equipment requirements, manufacturing cost, and intellectual-property exposure. The tradeoff is that matrix systems can be more sensitive to excipient grade and process conditions.

A multiparticulate or coated-pellet approach could create a differentiated product with improved release control, but it would increase manufacturing complexity. It may be justified only if the developer can demonstrate a meaningful commercial benefit, such as lower peak exposure, reduced gastrointestinal intolerance, or a more flexible dosing profile.

What FDA regulatory pathway applies to a PROQUIN XR generic?

A generic PROQUIN XR product would generally be pursued through an abbreviated new drug application under section 505(j) of the Federal Food, Drug, and Cosmetic Act. The principal requirements would include pharmaceutical equivalence, comparative bioavailability, manufacturing controls, stability, and compliance with current good manufacturing practice.

For an extended-release product, the development burden is higher than for immediate-release ciprofloxacin. A sponsor must establish that the proposed product has comparable release behavior and systemic exposure. Depending on FDA requirements, studies may include:

• Single-dose fasting bioequivalence
• Single-dose fed bioequivalence
• Comparative dissolution across multiple media
• Strength and dose proportionality assessments
• Alcohol-dose-dumping evaluation where relevant
• In vitro release testing across production-scale batches

The excipient list does not have to be identical to PROQUIN XR's list. The generic product can use different excipients if it meets regulatory and performance requirements. A qualitatively and quantitatively similar formulation can reduce development risk, but it may also limit opportunities to create a lower-cost or technically superior product.

What is the Orange Book status of PROQUIN XR?

PROQUIN XR was approved as NDA 21-473. The original product's market protection was associated with a new extended-release dosage form rather than new molecular-entity exclusivity. Ciprofloxacin itself has long been off patent.

The relevant commercial conclusions are:

Protection category	Assessment
New chemical entity exclusivity	Not applicable
Original drug patent protection	Expired or no longer a practical barrier to ordinary generic entry
Extended-release dosage-form protection	Historical protection; no longer sufficient to block market entry
Method-of-use protection	Potentially relevant only if an enforceable, listed claim remains
Orange Book-listed patents	Must be assessed against the current FDA listing for NDA 21-473
Generic entry pathway	505(j) ANDA, subject to applicable FDA requirements
Biosimilar pathway	Not applicable

PROQUIN XR is a small-molecule drug product, not a biologic. Biosimilar risk is therefore irrelevant. The competitive risk comes from ANDA applicants, authorized-generic structures, alternative ciprofloxacin products, and non-ciprofloxacin treatments for urinary tract infection.

When does PROQUIN XR lose exclusivity?

The meaningful commercial exclusivity for PROQUIN XR has already expired. The product was approved in 2004, and any three-year exclusivity associated with the new dosage form would have ended years ago. Patent protection for the original extended-release technology is also not a current barrier to generic development in the ordinary U.S. market.

The practical question is no longer when the original product loses exclusivity. It is whether any current Orange Book-listed patent, litigation stay, pediatric exclusivity, or regulatory discontinuation issue affects a specific ANDA. Those issues must be analyzed at the NDA and patent-listing level rather than inferred from the original approval date.

Are there Paragraph IV challenges to PROQUIN XR?

A Paragraph IV certification would be relevant if a current ANDA applicant asserted that a listed patent was invalid, unenforceable, or not infringed. Because PROQUIN XR's core exclusivity is historical, a new Paragraph IV dispute would likely concern a residual formulation, method-of-use, or release-control patent rather than ciprofloxacin itself.

The commercial significance of a Paragraph IV challenge depends on:

1. Whether the challenged patent is still listed in the Orange Book.
2. Whether the ANDA contains a Paragraph IV certification or a section viii statement.
3. Whether the NDA holder files an infringement action within 45 days.
4. Whether a 30-month stay applies.
5. Whether the patent claims cover the proposed formulation.
6. Whether the applicant qualifies for 180-day generic exclusivity.

A developer should not assume that a patent appearing in historical prosecution records remains enforceable or Orange Book-listed. Orange Book status and current court dockets control the entry analysis.[2,3]

What patent claims could protect a new PROQUIN XR-type product?

A new commercial product could seek protection around technical features rather than the ciprofloxacin molecule. Potential claim categories include:

Formulation patents

Potential formulation claims could cover:

• Specific HPMC viscosity grades
• Defined polymer-to-drug ratios
• Dual-polymer matrices
• Specific lubricant combinations
• Controlled porosity
• Coated matrix tablets
• Release profiles across specified pH conditions
• Reduced food effect
• Reduced alcohol sensitivity
• Defined impurity or degradation limits

A formulation patent is stronger when it claims a measurable technical result linked to a narrow composition. A broad claim covering ciprofloxacin plus a generic sustained-release polymer would face a greater invalidity and obviousness risk.

Method-of-use patents

A method-of-use patent could cover once-daily treatment of a narrowly defined infection population, treatment duration, or administration condition. Its commercial value would be limited if the FDA label does not support the claimed use or if physicians can prescribe the generic product for the same indication under ordinary medical practice.

Manufacturing patents

Manufacturing claims could address:

• Continuous blending
• Controlled granulation
• Low-shear lubricant incorporation
• Compression of high-drug-load matrices
• Film coating that avoids release-rate changes
• In-process dissolution control
• Moisture-control packaging

Manufacturing patents may create licensing value, but they are difficult to enforce against a competitor unless the process can be identified from the finished product or through discovery.

What commercial opportunities exist for PROQUIN XR excipients?

Generic extended-release ciprofloxacin

The clearest opportunity is a lower-cost generic or authorized-generic product. The main value drivers are:

• Reliable bioequivalence
• Low-cost tablet manufacture
• Stable dissolution after scale-up
• Supplier flexibility
• Reduced batch failure risk
• Competitive wholesale pricing

Excipient supplier partnerships

Excipient manufacturers can support differentiated development through:

• High-consistency HPMC grades
• Co-processed direct-compression excipients
• Low-hydrophobicity lubricants
• Moisture-resistant coating systems
• Excipient systems designed for continuous manufacturing

A supplier that can provide regulatory documentation, multiple manufacturing sites, and robust change-control support may capture more value than a supplier offering the lowest unit price.

Lifecycle reformulation

A reformulated product could target easier swallowing, lower tablet weight, improved packaging stability, or a more predictable fed-state profile. The commercial potential is limited by the low value of ciprofloxacin and the availability of inexpensive immediate-release alternatives.

Non-U.S. markets

Markets with continued demand for branded or generic extended-release antibiotics may offer opportunities where once-daily adherence has greater commercial value. Geographic patent barriers are likely to be limited because the core drug and original release technology are mature. Regulatory requirements, local reference-product rules, and procurement pricing will determine viability.

How does PROQUIN XR compare with immediate-release ciprofloxacin?

Attribute	PROQUIN XR	Immediate-release ciprofloxacin
Dosing	Once daily	Usually twice daily
Formulation complexity	Higher	Lower
Excipient sensitivity	High	Moderate
Bioequivalence burden	Higher	Lower
Manufacturing cost	Higher	Lower
Adherence potential	Better for some patients	More frequent dosing
Generic competition	Limited by ER development burden	Broad
Differentiation potential	Release profile and convenience	Price and supply

The once-daily proposition is commercially meaningful only if the extended-release product remains cost-competitive and clinically appropriate. The formulation must deliver a consistent release profile without creating a significant food effect or manufacturing penalty.

What generic launch risks exist?

The principal launch risks are:

1. Failure to match the reference dissolution profile.
2. Food-effect differences that alter exposure.
3. Batch variability from HPMC grade changes.
4. Excessive lubricant mixing that slows release.
5. Scale-up changes in granulation, compression, or coating.
6. Limited market demand because immediate-release ciprofloxacin is inexpensive.
7. Antibiotic stewardship pressures that reduce utilization.
8. Product discontinuation or procurement concentration.
9. Difficulty establishing a durable price premium.
10. Residual Orange Book or litigation issues tied to a specific ANDA.

The strongest development case is a low-cost, technically simple tablet with multiple qualified excipient suppliers and a clear regulatory pathway.

Key Takeaways

• PROQUIN XR is an extended-release ciprofloxacin hydrochloride 500 mg tablet approved for once-daily treatment of uncomplicated urinary tract infections.
• Hypromellose is the primary release-controlling excipient and the most important formulation-development variable.
• Microcrystalline cellulose, lubricant selection, tablet porosity, and compression conditions materially affect dissolution and bioequivalence.
• The original product's exclusivity has expired as a practical commercial barrier.
• Biosimilar risk does not apply because ciprofloxacin is a small molecule.
• Generic opportunity remains, but the market is constrained by inexpensive immediate-release ciprofloxacin and low antibiotic pricing.
• The strongest IP opportunities involve specific matrix compositions, measurable release characteristics, manufacturing processes, and differentiated stability or food-effect performance.
• Excipient suppliers can create value through grade consistency, regulatory support, supply resilience, and co-processed systems.
• A successful generic launch depends on dissolution control, scale-up robustness, and low manufacturing cost more than on broad molecular patent protection.

FAQs

Can a generic PROQUIN XR tablet use different excipients?

Yes. An ANDA applicant can use a different excipient system if the product satisfies FDA requirements for safety, quality, pharmaceutical equivalence, bioequivalence, and performance.

Is hypromellose interchangeable across suppliers?

No. Different HPMC grades can vary in viscosity, substitution, particle size, hydration, and release behavior. Supplier changes require formulation and dissolution assessment.

Does ciprofloxacin have biosimilar competition?

No. Ciprofloxacin is a chemically synthesized small molecule. Competition occurs through generic-drug pathways, not the biosimilar pathway.

Can a new ciprofloxacin extended-release formulation receive patent protection?

Yes, if the formulation or manufacturing process satisfies patentability requirements. Protection is more credible for narrow, technically defined compositions or demonstrated release characteristics than for broad sustained-release claims.

Is a PROQUIN XR reformulation commercially attractive?

It can be attractive where it reduces manufacturing cost, improves release consistency, supports once-daily adherence, or creates a defensible formulation position. The opportunity is weaker where the product must compete solely on price with immediate-release ciprofloxacin.

References

1. U.S. National Library of Medicine. (n.d.). DailyMed: PROQUIN XR- ciprofloxacin hydrochloride tablet, extended release. National Institutes of Health.

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

3. U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs, NDA 021473. FDA.

4. U.S. Food and Drug Administration. (2013). Guidance for industry: Bioequivalence studies with pharmacokinetic endpoints for drugs submitted under an ANDA. FDA.

5. U.S. Pharmacopeial Convention. (2024). United States Pharmacopeia and National Formulary. USP.