List of Excipients in Branded Drug PROBENECID AND COLCHICINE

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Generic Drugs Containing PROBENECID AND COLCHICINE

Company	Ingredient	NDC	Excipient
Actavis Pharma Inc	probenecid and colchicine	0591-5325	CELLULOSE, MICROCRYSTALLINE
Actavis Pharma Inc	probenecid and colchicine	0591-5325	MAGNESIUM STEARATE
Actavis Pharma Inc	probenecid and colchicine	0591-5325	SILICON DIOXIDE
Actavis Pharma Inc	probenecid and colchicine	0591-5325	SODIUM LAURYL SULFATE

What are the Most Frequently-Used Excipients in PROBENECID AND COLCHICINE?

# Of NDCs	Excipient
3	CELLULOSE, MICROCRYSTALLINE
5	MAGNESIUM STEARATE
2	MICROCRYSTALLINE CELLULOSE 101
2	POVIDONE K90

Probenecid and Colchicine Excipient Strategy, Patent Position, and Commercial Opportunities

Last updated: October 8, 2026

Probenecid and colchicine is an established fixed-dose combination for gout management, generally supplied as an immediate-release tablet containing probenecid 500 mg and colchicine 0.5 mg. Its commercial opportunity is primarily generic supply, formulation improvement, manufacturing efficiency, and differentiated packaging rather than new chemical entity exclusivity. The combination has limited apparent patent protection, while regulatory execution depends on demonstrating consistent assay, content uniformity, dissolution, and bioequivalence for both active ingredients.

What is the commercial and regulatory status of probenecid and colchicine?

Probenecid and colchicine tablets combine:

Component	Typical strength	Pharmacologic role
Probenecid	500 mg	Reduces renal uric acid reabsorption and increases uric acid excretion
Colchicine	0.5 mg	Reduces inflammation associated with gout flares

The product is an oral immediate-release fixed-dose combination. It is used in chronic gout management, particularly when urate-lowering treatment is required and colchicine is used to reduce inflammatory flares during therapy.

The combination is commercially mature. Probenecid was approved in the United States decades ago, and colchicine has a long history of use. The relevant commercial product is commonly identified as probenecid and colchicine tablets or by the historical brand name ColBenemid. FDA labeling identifies the product as a prescription tablet containing probenecid and colchicine [1].

The primary commercial constraints are:

• Small and potentially declining market size compared with allopurinol and febuxostat.
• Limited ability to command a premium for an unmodified immediate-release tablet.
• Low active-ingredient dose for colchicine, which increases content-uniformity sensitivity.
• Potential safety concerns from colchicine exposure, renal impairment, hepatic impairment, and drug interactions.
• Competition from separately prescribed probenecid and colchicine products.
• Limited physician use of probenecid in patients with renal impairment or a history of uric acid nephrolithiasis.

What excipients are used in probenecid and colchicine tablets?

Commercial immediate-release versions generally use conventional tablet excipients, including a filler, disintegrant, lubricant, glidant, and, in some formulations, a film-coating system. The exact composition depends on the manufacturer and dosage form.

A representative excipient platform may include:

Excipient function	Suitable candidates	Development purpose
Diluent	Microcrystalline cellulose, lactose monohydrate, dibasic calcium phosphate	Provides tablet mass and improves compression
Binder	Povidone, copovidone, pregelatinized starch	Improves granule and tablet strength
Disintegrant	Crospovidone, croscarmellose sodium, sodium starch glycolate	Promotes rapid tablet breakup
Glidant	Colloidal silicon dioxide	Improves powder flow and blend uniformity
Lubricant	Magnesium stearate, sodium stearyl fumarate	Reduces ejection force and tooling adhesion
Moisture-control excipient	Low-moisture grades of cellulose or calcium phosphate	Reduces hydrolytic and physical instability risk
Film coat	Hypromellose, polyethylene glycol, titanium dioxide, iron oxides	Improves appearance, handling, swallowability, and light protection

A conventional label may list lactose, microcrystalline cellulose, sodium starch glycolate, colloidal silicon dioxide, magnesium stearate, and coating materials. The approved product-specific label and current DailyMed entry control the legally relevant composition [1,2].

Which excipient risks are most important?

The principal formulation risks relate to colchicine’s low dose and probenecid’s relatively high tablet load.

Colchicine at 0.5 mg represents a small fraction of total tablet weight. Blend segregation, inadequate geometric dilution, or inconsistent granulation can cause unacceptable content variability. A formulation should use a validated premixing sequence, controlled particle-size distribution, and robust in-process sampling.

Probenecid contributes most of the tablet mass and may affect blend density, compactability, and dissolution. The formulation should avoid excessive lubricant levels or over-lubrication because these can slow disintegration and dissolution.

The primary excipient controls should include:

1. Particle-size specifications for both active ingredients.
2. Defined preblend and main-blend times.
3. Blend-uniformity sampling designed around the low colchicine dose.
4. Tight magnesium stearate addition and lubrication controls.
5. Dissolution testing for both probenecid and colchicine.
6. Moisture and temperature controls during granulation, compression, and packaging.
7. Stability testing under ICH long-term and accelerated conditions [3].

How should the excipient strategy be designed for a generic product?

The lowest-risk strategy is a conventional immediate-release tablet that closely reproduces the reference product’s performance without unnecessary excipient innovation.

Recommended baseline formulation

A practical development sequence is:

• Use microcrystalline cellulose or lactose as the primary diluent.
• Use crospovidone or sodium starch glycolate as the disintegrant.
• Use colloidal silicon dioxide to improve flow.
• Use magnesium stearate at the lowest level that provides acceptable ejection performance.
• Use a thin film coat only if it improves handling, taste, appearance, or light protection.
• Prefer excipient grades with established regulatory precedent in oral immediate-release tablets.

A direct-compression formulation may reduce manufacturing cost, but wet granulation can provide better control of low-dose colchicine distribution if powder-flow or segregation problems occur. Roller compaction is an alternative where water exposure is undesirable, although it can alter tablet porosity and dissolution.

Which excipient combinations offer commercial differentiation?

The strongest differentiation opportunities are operational rather than patent-driven:

• Low-moisture formulation for improved stability.
• High-flow excipient system for direct compression.
• Smaller tablet through higher-density diluents.
• Film coating that improves swallowing and product identification.
• Color-coded strength or packaging to reduce dispensing errors.
• Unit-dose blister packaging for adherence and controlled dispensing.
• Bottle packaging with a high-performance desiccant closure.
• Split-tablet design only if dose uniformity and tablet-break testing support the claim.

A formulation patent may be available for a genuinely novel stability system, dissolution profile, manufacturing process, or packaging configuration. A simple substitution of one conventional diluent or disintegrant for another generally provides weak patent differentiation and may not justify enforcement costs.

What patents protect probenecid and colchicine?

The active ingredients and historical fixed-dose combination are mature pharmaceutical technologies. Core composition-of-matter patent protection for probenecid and colchicine has expired. A commercial developer should not assume that the base combination has meaningful remaining composition-of-matter exclusivity.

Potentially relevant rights fall into four categories:

Rights category	Likely commercial relevance
Active-ingredient patents	Generally expired for these long-established molecules
Fixed-dose combination patents	Likely expired or limited in scope for the historical immediate-release product
Formulation patents	Potentially relevant if a new release profile, stability system, or dosage form is developed
Method-of-use patents	Potentially relevant only for narrow, specifically claimed patient populations or treatment regimens

The FDA Orange Book is the controlling source for patents and regulatory exclusivity listed against an approved reference product [4]. An applicant should review the current Orange Book entry for the relevant reference listed drug, including any listed patents, pediatric exclusivity, and marketing exclusivity.

When does probenecid and colchicine lose exclusivity?

The core products are already outside the normal new-drug exclusivity period. The commercial issue is therefore not the expiration of a major remaining patent term. It is whether a generic applicant can obtain approval without infringing any still-listed formulation, method, or manufacturing patent.

For an ANDA applicant, the relevant certification may be:

• Paragraph I, if no patent information is listed.
• Paragraph II, if the patent has expired.
• Paragraph III, if the applicant will wait until patent expiration.
• Paragraph IV, if the applicant asserts that a listed patent is invalid, unenforceable, or not infringed.

A Paragraph IV filing can create 30 months of FDA approval stays if the patent holder or NDA sponsor brings a qualifying infringement action within the statutory period [5]. The practical risk appears lower for this mature combination than for recently approved small-molecule products, but the current Orange Book record remains controlling.

What is the Orange Book status of probenecid and colchicine?

The Orange Book determines whether FDA-listed patents or exclusivities affect an ANDA for the reference product. The relevant review should cover:

• Reference listed drug designation.
• Active ingredient and strength.
• Dosage form.
• Applicant and marketing status.
• Listed patents.
• Patent expiration dates.
• Exclusivity codes.
• Whether the product is currently marketed.

A product may remain listed in the Orange Book even when commercial availability is limited. Conversely, a product may have no meaningful remaining patent barrier but still present regulatory risk because of reference-product discontinuation, limited sourcing, or uncertainty over the appropriate ANDA reference.

A sponsor should distinguish between:

1. Patent protection listed in the Orange Book.
2. Unlisted patents that may still create litigation risk.
3. Regulatory exclusivity.
4. Supply and manufacturing rights.
5. Trademark and trade-dress rights.

These rights have different effects on generic launch timing.

Which regulatory pathway is most appropriate?

ANDA pathway

An ANDA is the preferred route for a conventional generic immediate-release tablet if an appropriate reference listed drug is available. The applicant must establish pharmaceutical equivalence and bioequivalence and meet current quality requirements under 21 C.F.R. Part 314 [6].

The development package should address:

• Identity and strength of both active ingredients.
• Assay and impurities.
• Content uniformity, particularly for colchicine.
• Dissolution for both active ingredients.
• Stability.
• Microbial quality where applicable.
• Comparative bioequivalence.
• Inactive-ingredient justification.
• Container-closure suitability.

505(b)(2) pathway

A 505(b)(2) application may be appropriate for:

• Modified release.
• A new dosage form.
• A lower-dose or alternative-strength product.
• A new packaging or administration design.
• A clinically differentiated combination.
• A product using published literature or FDA findings for part of its approval basis.

The 505(b)(2) route carries greater development cost and may trigger patent certification and litigation issues against listed patents. It can create a stronger commercial position if the product solves a clinically relevant problem, such as adherence, swallowing difficulty, or dosing flexibility [7].

What formulation patents could create commercial value?

A credible patent strategy would focus on measurable technical advantages. Potential claim areas include:

Low-dose content-uniformity technology

Claims could cover a specific premixing process, particle-size distribution, ordered mixture, or granulation method that maintains colchicine uniformity at commercial scale.

Stability-enhanced composition

A patent could target a specific moisture-control system, antioxidant-free composition, protective coating, or packaging combination that improves assay stability or impurity control.

Modified-release dosage form

A sustained-release product could separate chronic urate-lowering therapy from flare prophylaxis or provide different release profiles for probenecid and colchicine. This would require substantial pharmacokinetic and clinical justification because the two ingredients have different therapeutic roles and safety considerations.

Multiparticulate or sprinkle formulation

A capsule containing multiparticulates could address swallowing difficulty. The product would require control of dose uniformity, release behavior, and administration with food or soft foods.

Adherence-oriented packaging

Calendarized blister packs or unit-dose cartons may have commercial value, although packaging claims generally provide weaker exclusivity than composition or process claims.

What generic entry risks exist?

Generic entry risk is high for a conventional immediate-release version because:

• The active ingredients are old.
• The product has a simple oral dosage form.
• Conventional excipients are available from multiple suppliers.
• Manufacturing processes are well established.
• No biosimilar pathway is relevant.
• The likely regulatory route is an ANDA rather than a complex clinical program.

The main barriers are execution risks:

Risk	Commercial impact
Colchicine content variability	Batch failure, FDA deficiency, recall exposure
Dissolution mismatch	Bioequivalence failure or additional studies
Reference-product sourcing	Delayed comparative testing
Limited market size	Weak return on development investment
Low price expectations	Margin compression
Colchicine safety concerns	Pharmacovigilance and labeling burden
Supplier concentration	Cost and continuity risk

Which companies are challenging the product?

The product is in a mature generic category with multiple historical manufacturers and distributors. No specific current Paragraph IV challenger, active litigation matter, or settlement agreement should be treated as controlling without a current review of FDA records, Patent Trial and Appeal Board proceedings, PACER filings, and commercial listings.

For this product class, competitive assessment should focus less on branded patent litigation and more on:

• Number of active ANDA holders.
• Current marketed suppliers.
• National Drug Code activity.
• Wholesale acquisition price.
• Back-order frequency.
• API supplier concentration.
• Manufacturing location.
• Product discontinuation notices.
• Hospital and retail contracting.

How does probenecid and colchicine compare with competing gout products?

Product	Main role	Commercial position	Patent risk
Probenecid and colchicine	Uricosuric therapy plus flare prophylaxis	Niche fixed-dose combination	Low for core product
Probenecid alone	Chronic urate lowering	Generic, inexpensive	Low
Colchicine alone	Flare treatment and prophylaxis	Larger and more recognized market	Product-specific rights may vary
Allopurinol	First-line urate lowering	Dominant generic therapy	Low for core product
Febuxostat	Urate lowering	Higher-value branded and generic competition	Product-specific patent history
Pegloticase	Refractory gout	Specialty biologic	Biologic and administration-related barriers

The combination’s advantage is convenience. Its disadvantage is dose inflexibility. A physician cannot independently adjust probenecid and colchicine exposure through a fixed-dose tablet. That limitation reduces the product’s appeal for patients with renal impairment, changing flare risk, or colchicine interaction concerns.

What licensing and partnering opportunities exist?

Licensing value is more likely to arise from manufacturing and formulation capabilities than from ownership of the historical drug combination.

Potential transaction structures include:

• Acquisition or licensing of an approved ANDA.
• Contract manufacturing of the finished tablet.
• Regional commercialization rights.
• Private-label supply for pharmacy and institutional channels.
• In-license of a low-dose content-uniformity platform.
• Co-development of a modified-release or adherence-oriented product.
• API supply agreements with dual-source qualification.
• Product bundle agreements with probenecid or colchicine monotherapy.

A buyer should value the product based on net sales, gross margin, supply reliability, ANDA status, manufacturing capacity, and market concentration. Historical sales alone are insufficient because mature generic products can experience rapid price erosion after additional entrants.

What geographic markets offer the best opportunity?

The United States offers a clear ANDA pathway but has intense generic price competition. Canada, Europe, Australia, and selected emerging markets may offer opportunities where fixed-dose gout products are available through national reimbursement or hospital channels.

Geographic diligence should assess:

• Whether the fixed-dose combination is approved.
• Whether probenecid is commonly used in local treatment guidelines.
• Local colchicine prescription controls.
• Patent and supplementary protection certificate status.
• Reference-product availability.
• Pharmacopoeial requirements.
• Reimbursement and tender pricing.
• Local manufacturing or serialization rules.

The strongest initial opportunity is generally a market with an established reference product, predictable generic approval pathway, and limited incumbent supply.

What manufacturing and intellectual-property barriers matter most?

The manufacturing barrier is low to moderate. The technical challenge is not synthesizing either active ingredient. It is producing a reproducible low-dose combination tablet with acceptable dissolution and stability at competitive cost.

Critical manufacturing controls include:

• API particle-size control.
• Colchicine premixing.
• Segregation prevention.
• Blend uniformity.
• Compression-force control.
• Lubrication time.
• Tablet hardness and friability.
• Dissolution profile.
• Moisture exposure.
• Packaging integrity.

The best defensible intellectual property would claim a specific composition or process that produces a measurable improvement. A broad claim to probenecid plus colchicine in a conventional tablet is likely to face validity and obviousness challenges given the long history of the combination.

Key Takeaways

• Probenecid and colchicine is a mature immediate-release fixed-dose combination, typically containing 500 mg of probenecid and 0.5 mg of colchicine.
• The core active ingredients and historical combination are generally outside meaningful composition-of-matter exclusivity.
• The most important formulation issue is uniform distribution of the low-dose colchicine component.
• A conventional ANDA is the principal regulatory route for a standard generic tablet.
• A 505(b)(2) strategy may support modified release, new dosage forms, or clinically meaningful adherence improvements.
• Commercial value is concentrated in reliable supply, low-cost manufacturing, packaging, and selective formulation differentiation.
• Patent value is stronger for a validated stability, content-uniformity, release-control, or manufacturing technology than for a conventional excipient substitution.
• Biosimilar risk is not relevant because both active ingredients are small molecules.
• Generic entry risk is high, but market attractiveness is constrained by limited demand and price erosion.
• Current Orange Book listings, FDA marketing status, Paragraph IV activity, and litigation must be verified before launch or transaction execution.

FAQs

Can lactose be used in probenecid and colchicine tablets?

Yes. Lactose is a conventional tablet diluent and may be suitable when compatibility, moisture sensitivity, compression behavior, and labeling requirements are acceptable. The selected grade should support blend uniformity and dissolution.

Is colchicine considered a narrow therapeutic index drug?

Colchicine has a narrow safety margin and clinically important toxicity risks, particularly in overdose and in patients with renal or hepatic impairment. The formulation should therefore prioritize dose uniformity, accurate labeling, and controlled manufacturing.

Can a probenecid and colchicine tablet be marketed as an over-the-counter product?

A fixed-dose product containing these active ingredients would generally require prescription-drug development and regulatory review. An over-the-counter pathway would require an applicable FDA monograph or a separate regulatory basis, neither of which should be assumed for this combination.

Is a modified-release probenecid and colchicine product commercially attractive?

It could be attractive if it improves adherence or separates the pharmacokinetic profiles of the two ingredients. The development burden would be materially higher than for a conventional generic because release performance, pharmacokinetics, clinical utility, and patentability would all require support.

What is the strongest patent strategy for a new product?

The strongest strategy would usually target a specific composition or manufacturing process that solves a documented technical problem, such as colchicine content uniformity, moisture-driven instability, controlled release, or improved patient administration.

References

1. U.S. Food and Drug Administration. (n.d.). Probenecid and colchicine tablets, USP: Prescribing information. FDA-approved labeling.

2. National Library of Medicine. (n.d.). DailyMed: Probenecid and colchicine tablet. U.S. National Library of Medicine.

3. International Council for Harmonisation. (2003). Q1A(R2): Stability testing of new drug substances and products. ICH.

4. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.

5. U.S. Food and Drug Administration. (2024). Abbreviated new drug application approvals and patent certifications. FDA, Center for Drug Evaluation and Research.

6. Electronic Code of Federal Regulations. (2024). 21 C.F.R. Part 314: Applications for FDA approval to market a new drug. U.S. Government Publishing Office.

7. U.S. Food and Drug Administration. (2022). Applications covered by Section 505(b)(2). FDA, Center for Drug Evaluation and Research.