List of Excipients in Branded Drug DARVON-N

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DARVON-N Excipient Strategy and Commercial Opportunities

Last updated: October 28, 2026

DARVON-N is the discontinued brand for propoxyphene napsylate, an opioid analgesic formerly marketed in 100 mg tablets. Its commercial position is severely constrained by withdrawal from the U.S. market after FDA-linked safety findings involving dose-related cardiac toxicity. Excipient optimization cannot address the principal risk, which is associated with the active ingredient and its metabolites. The viable commercial paths are limited to historical generic analysis, legacy-market assessment outside the United States, and research into safer replacement analgesics rather than direct DARVON-N redevelopment.

What is DARVON-N and which active ingredient did it contain?

DARVON-N contained propoxyphene napsylate, a weak opioid analgesic. The product was distinct from formulations containing propoxyphene hydrochloride and from combination products such as propoxyphene-acetaminophen products.

Product attribute	DARVON-N
Active ingredient	Propoxyphene napsylate
Historical strength	100 mg per tablet
Dosage form	Immediate-release oral tablet
Drug class	Opioid analgesic
Historical U.S. sponsor	Xanodyne Pharmaceuticals
U.S. regulatory status	Withdrawn from the market
Current U.S. commercial status	No lawful new-product opportunity based on the former brand
Biosimilar relevance	None
Primary commercial barrier	Active-ingredient safety, not excipient performance

Propoxyphene was marketed for short-term management of mild to moderate pain. The FDA concluded that available data showed a significant risk of serious or potentially fatal cardiac arrhythmias, including at therapeutic doses. FDA requested withdrawal of propoxyphene products in 2010, and the product was removed from the U.S. market shortly afterward (U.S. Food and Drug Administration, 2010a).

What excipients were used in DARVON-N tablets?

Historical U.S. labeling identifies conventional immediate-release tablet excipients. Public labeling for propoxyphene napsylate products has identified excipient classes including microcrystalline cellulose, lactose, crospovidone, povidone, magnesium stearate, colloidal silicon dioxide, and sodium lauryl sulfate, although the precise qualitative and quantitative composition can vary by manufacturer and manufacturing period.

The historical excipient strategy was conventional:

Excipient function	Likely formulation role
Microcrystalline cellulose	Diluent and tablet-structure former
Lactose	Filler and compression aid
Crospovidone	Superdisintegrant
Povidone	Binder
Magnesium stearate	Lubricant
Colloidal silicon dioxide	Glidant and flow aid
Sodium lauryl sulfate	Wetting or dissolution aid

The relevant formulation objective was rapid disintegration and conventional immediate release. DARVON-N was not positioned as an extended-release, abuse-deterrent, orally disintegrating, or modified-release product.

Exact excipient identity must be tied to the specific historical manufacturer and National Drug Code. FDA labeling and DailyMed records should be treated as the primary sources for product-specific composition rather than relying on a general propoxyphene formulation.

Can excipient changes make DARVON-N commercially viable?

No. Excipient changes cannot eliminate the principal safety concern associated with propoxyphene.

Propoxyphene and its metabolite, norpropoxyphene, were linked to cardiac conduction abnormalities and QT-interval prolongation. The FDA stated that the risk was present even at therapeutic doses and that the analgesic benefit was insufficient to outweigh the cardiac risk (U.S. Food and Drug Administration, 2010a).

An excipient reformulation could alter:

• Tablet hardness
• Disintegration time
• Dissolution profile
• Moisture sensitivity
• Manufacturing yield
• Taste and swallowability
• Packaging stability
• Physical tamper resistance

It could not remove the active metabolite, change the pharmacologic mechanism, or reliably prevent cardiotoxicity. A new formulation with a different release profile could create further exposure concerns if it increased peak concentrations, prolonged exposure, or complicated dose control.

Would an abuse-deterrent formulation create a new opportunity?

An abuse-deterrent design would not solve the core regulatory issue. Abuse-deterrent formulations address manipulation or nonoral routes of administration. The FDA withdrawal was based primarily on intrinsic cardiac risk and an unfavorable benefit-risk balance, not on tablet tampering.

A crush-resistant tablet, polymer matrix, or sequestered formulation would therefore face two separate issues:

1. It would require evidence that the new dosage form remains safe and effective.
2. It would not remove the cardiac risk that led to withdrawal.

An abuse-deterrent label claim would require substantial comparative abuse-potential data and FDA review under applicable opioid guidance. It would not be a simple generic formulation change.

What is the FDA status of DARVON-N?

DARVON-N is not a commercially active U.S. product. FDA requested withdrawal of all propoxyphene products in November 2010 after reviewing new cardiac safety data. FDA stated that propoxyphene should no longer be used and that companies should voluntarily withdraw products containing the ingredient (U.S. Food and Drug Administration, 2010a).

FDA regulatory timeline

Date	Regulatory event
1950s	Propoxyphene products entered the U.S. market
2009	FDA required stronger boxed-warning language and medication-guide changes after earlier safety review
July 2010	FDA required a new safety study after continuing concern regarding cardiac effects
November 2010	FDA requested withdrawal of propoxyphene products
Late 2010 to early 2011	U.S. products were withdrawn
2011	FDA communicated that remaining patients should transition to alternative treatment

FDA’s action followed a randomized cardiac safety study showing QT-interval prolongation in patients receiving therapeutic doses. The agency determined that the risks outweighed the limited pain-relief benefit.

What is the Orange Book status of DARVON-N?

DARVON-N does not present a current U.S. Orange Book opportunity. The product has been discontinued, and the relevant propoxyphene product listings are historical rather than an active basis for commercial launch.

The Orange Book distinguishes between discontinued products and products that remain eligible for generic competition. A discontinued reference product does not automatically create a viable abbreviated new drug application pathway. The applicant must establish the applicable reference product, regulatory eligibility, bioequivalence pathway, and safety basis.

Because propoxyphene products were withdrawn for safety reasons, an ANDA strategy directed at reproducing DARVON-N would face a fundamental regulatory obstacle. A formulation that is pharmaceutically equivalent to the withdrawn product would inherit the same active-ingredient risk.

Are there DARVON-N patents or Paragraph IV opportunities?

The meaningful patent estate for DARVON-N has expired or ceased to have practical commercial value. Propoxyphene is an old active ingredient, and the original product patents are not a current barrier to entry.

IP category	DARVON-N assessment
Original compound patents	Expired
Basic tablet formulation patents	Expired or commercially immaterial
Method-of-use patents	No meaningful current protection supporting U.S. launch
Orange Book-listed patents	No current strategic value
Paragraph IV opportunity	Technically academic and commercially unattractive
Patent litigation risk	Low relative to regulatory and product-liability risk
Trade-secret value	Limited to historical manufacturing know-how

A Paragraph IV certification would challenge an unexpired patent listed for a reference product. That mechanism does not solve a withdrawn-product safety problem. Even if a generic applicant defeated a patent, FDA approval would still depend on the agency’s determination that the product could lawfully be marketed.

The more material legal risks would likely arise from product liability, labeling, pharmacovigilance, and regulatory enforcement rather than patent infringement.

Which companies challenged or litigated DARVON-N?

The principal historical dispute involved FDA safety review and withdrawal rather than a durable patent contest. Xanodyne Pharmaceuticals, the then-marketing company, agreed to withdraw propoxyphene products after FDA action.

Propoxyphene products also generated substantial product-liability exposure before and after withdrawal. Claims generally focused on alleged inadequate warnings, cardiac injury, overdose, and wrongful death. Those cases are distinct from patent litigation and do not create an entry path for a new manufacturer.

No current competitive patent litigation is material to a DARVON-N launch strategy.

What geographic coverage remains for propoxyphene products?

Propoxyphene has been withdrawn or restricted in multiple jurisdictions. The European Medicines Agency recommended withdrawal of marketing authorizations for propoxyphene-containing medicines in 2009 because of concerns about overdose risk and limited therapeutic benefit (European Medicines Agency, 2009).

Market status can differ by country because withdrawal dates, local approvals, and supply records vary. A country-specific opportunity would require review of:

• Local marketing authorization status
• National formulary treatment
• Controlled-substance scheduling
• Pharmacovigilance requirements
• Local patent and data-exclusivity records
• Import restrictions
• Product-liability exposure
• Availability of safer analgesic alternatives

The broad international trend has been contraction rather than expansion. A country that still has an old registration would not necessarily represent a viable commercial market.

How should an excipient strategy be designed for a replacement product?

The strongest commercial opportunity is not a direct DARVON-N reformulation. It is a safer oral analgesic platform that uses excipient selection to improve tolerability, manufacturability, adherence, or abuse resistance without retaining propoxyphene.

Immediate-release replacement tablet

For a conventional immediate-release analgesic, the formulation target would be rapid and reproducible dissolution with robust tablet handling. A typical strategy would evaluate:

• Microcrystalline cellulose or mannitol as a filler
• Crospovidone or croscarmellose sodium as a disintegrant
• Povidone or copovidone as a binder
• Colloidal silicon dioxide as a flow aid
• Magnesium stearate or sodium stearyl fumarate as a lubricant
• Film coating for moisture protection, taste masking, and product identification

The excipient selection should be based on dissolution, tablet tensile strength, friability, blend uniformity, and stability. For a low-dose potent drug, segregation control and content uniformity may matter more than compression speed.

Abuse-deterrent opioid platform

If the replacement contains an opioid, potential formulation approaches include:

• High-hardness polymer matrices
• Gelling systems that resist syringeability
• Aversion agents
• Physical barriers to crushing
• Sequestered antagonist systems
• Nasal and injectable abuse-resistance testing

These approaches can support an FDA abuse-deterrent claim only if the product meets the relevant laboratory, pharmacokinetic, and human abuse-potential requirements. They do not substitute for a favorable benefit-risk profile.

Pediatric or geriatric dosage form

A nonopioid analgesic or safer opioid could support differentiated dosage forms such as:

• Low-swallowing-burden mini-tablets
• Orally disintegrating tablets
• Taste-masked granules
• Sprinkle capsules
• Liquid suspensions with controlled sedimentation

These opportunities are more defensible when linked to a clinically documented adherence problem and supported by a clear label strategy.

How strong is the DARVON-N patent estate?

The patent estate is weak for commercial purposes.

Patent strength depends on remaining term, enforceability, claim scope, regulatory relevance, and the existence of a commercially valuable product. DARVON-N performs poorly on each current metric:

Criterion	Assessment
Remaining composition-of-matter term	None of commercial significance
Formulation exclusivity	No meaningful active barrier identified
Regulatory exclusivity	None supporting a new U.S. launch
Clinical differentiation	Negative because of cardiac safety
Manufacturing complexity	Low to moderate
Generic substitution potential	Limited by withdrawal
Litigation leverage	Low
Licensing value	Minimal for the original product

A new patent could potentially cover a novel formulation or delivery system, but patentability would not establish marketability. A formulation patent directed to propoxyphene would still confront the safety record and FDA withdrawal.

What commercial opportunities remain?

The commercial opportunities fall into four categories, ranked by practical value.

Opportunity	Commercial assessment
Relaunch branded DARVON-N in the United States	Not commercially viable
Launch a propoxyphene generic	High regulatory and liability risk; poor opportunity
Acquire historical DARVON-N trademarks or formulation know-how	Low value
Develop a safer analgesic replacement	Most viable strategic path
License excipient or abuse-deterrent technology to other opioid developers	Potentially viable
Supply legacy markets outside the U.S.	Country-specific and high-risk
Develop nonopioid immediate-release analgesics	Stronger risk-adjusted opportunity

Revenue exposure from DARVON-N itself is effectively zero in the current U.S. market. Any valuation based on historical brand recognition should exclude U.S. product revenue unless a new active ingredient, new clinical program, and new FDA approval strategy are assumed.

What generic launch risks exist for DARVON-N?

A generic launch would face risks beyond ordinary ANDA development:

1. FDA may not accept a withdrawn propoxyphene product as a practical reference for approval.
2. The active ingredient has a documented cardiac safety problem.
3. Product labeling would require prominent warnings and potentially restricted use.
4. Pharmacovigilance costs would be high relative to likely demand.
5. Product-liability claims could materially exceed sales.
6. Payers and prescribers would favor safer alternatives.
7. International regulators may impose additional restrictions or refuse authorization.
8. A reformulation that changes exposure could require a new drug application rather than an ANDA.

The economic case is therefore unfavorable even if the historical patent estate is open.

Key Takeaways

• DARVON-N contained propoxyphene napsylate and was marketed as a 100 mg immediate-release tablet.
• Its historical excipients were conventional tablet ingredients, including fillers, binders, disintegrants, lubricants, and flow aids.
• Excipient optimization cannot correct propoxyphene-associated cardiac toxicity.
• FDA requested withdrawal of propoxyphene products in 2010, and DARVON-N has no meaningful current U.S. commercial position.
• The patent estate is effectively expired and does not create a valuable Paragraph IV strategy.
• Patent litigation is not the main risk; regulatory approval, cardiac safety, and product liability are.
• The strongest commercial opportunity is a safer analgesic replacement or licensing of formulation technology to active products with an acceptable benefit-risk profile.

FAQs

Is DARVON-N still available by prescription?

No. DARVON-N and other U.S. propoxyphene products were withdrawn after FDA concluded that cardiac risks outweighed the drug’s limited analgesic benefit.

What is the difference between DARVON-N and DARVOCET?

DARVON-N contained propoxyphene napsylate alone. DARVOCET products combined propoxyphene with acetaminophen. Both product categories were affected by the safety concerns surrounding propoxyphene.

Can a company patent a new DARVON-N formulation?

A genuinely novel formulation might satisfy patentability requirements, but a patent would not overcome the active ingredient’s safety record or guarantee FDA approval.

Is propoxyphene a candidate for a biosimilar program?

No. Biosimilars apply to biological products. Propoxyphene is a chemically synthesized small molecule, so any generic pathway would be based on small-molecule drug approval rules.

What is the best replacement strategy for a company holding DARVON-N know-how?

The strongest strategy is to apply the historical immediate-release manufacturing knowledge to a safer analgesic, including a nonopioid product or a clinically justified abuse-deterrent opioid formulation.

References

European Medicines Agency. (2009). European Medicines Agency recommends withdrawal of marketing authorisations for dextropropoxyphene-containing medicines. https://www.ema.europa.eu/

U.S. Food and Drug Administration. (2010a). FDA recommends against the continued use of propoxyphene. https://www.fda.gov/

U.S. Food and Drug Administration. (2010b). FDA drug safety communication: FDA recommends against the continued use of propoxyphene. https://www.fda.gov/

U.S. National Library of Medicine. (n.d.). DailyMed: Propoxyphene napsylate tablet labeling. https://dailymed.nlm.nih.gov/