Generic PROPOXYPHENE NAPSYLATE INN entry, drug patent expiration information and freedom to operate

Sponsor	Phase
Xanodyne Pharmaceuticals	Phase 4

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Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Xanodyne Pharm	DARVON-N	propoxyphene napsylate	TABLET;ORAL	016862-002	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Aaipharma Llc	DARVON-N	propoxyphene napsylate	SUSPENSION;ORAL	016861-001	Approved Prior to Jan 1, 1982		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Exclusivity Expiration

Last updated: September 7, 2026

Propoxyphene napsylate is a discontinued opioid analgesic with no meaningful current commercial market in the United States or European Union. Its financial trajectory moved from mature, declining branded sales to generic erosion and regulatory withdrawal. The principal value destruction came from cardiac-safety findings, overdose risk, market withdrawals and loss of prescriber confidence rather than patent expiry alone. No biosimilar or conventional generic-entry opportunity remains in the U.S. because propoxyphene products were withdrawn and are not marketed.

What is propoxyphene napsylate and how was it commercialized?

Propoxyphene napsylate is the napsylate salt of propoxyphene, a synthetic opioid formerly used for mild-to-moderate pain. The best-known U.S. brand was Darvon-N, while Darvocet combined propoxyphene with acetaminophen. Xanodyne Pharmaceuticals held the U.S. rights to Darvon and Darvocet before the products were withdrawn in 2010.

Propoxyphene was marketed for decades as a lower-potency oral analgesic. Its commercial position weakened as physicians gained access to non-opioid analgesics, tramadol and other opioid products with more favorable perceived safety profiles.

Product	Active ingredient	Commercial role	U.S. status
Darvon-N	Propoxyphene napsylate	Propoxyphene-only analgesic	Withdrawn in 2010
Darvon	Propoxyphene hydrochloride	Propoxyphene-only analgesic	Withdrawn in 2010
Darvocet-N	Propoxyphene napsylate plus acetaminophen	Combination analgesic	Withdrawn in 2010
Generic propoxyphene products	Propoxyphene salts, with or without acetaminophen	Low-cost alternatives	Withdrawn in 2010

The napsylate salt was used in Darvon-N and Darvocet-N. The safety concern applied to propoxyphene products generally, not only to the napsylate formulation.

When did propoxyphene napsylate lose market exclusivity?

Propoxyphene napsylate lost practical market exclusivity many years before regulatory withdrawal. The original propoxyphene composition patents expired decades ago, and multiple generic manufacturers entered the market. By the 2000s, the product was a mature generic medicine rather than a protected growth asset.

The commercial sequence was:

Period	Market event	Financial effect
1950s-1980s	Branded opioid launch and broad prescribing	High-margin branded revenue
1980s-1990s	Generic entry and growth of competing analgesics	Price erosion and share loss
2000s	Safety warnings and declining prescribing	Lower volume and weaker brand economics
2005-2007	Withdrawal from the United Kingdom and other markets	Reduced geographic revenue
2009	FDA advisory review of cardiac risk	Accelerated prescriber and payer abandonment
2010	U.S. market withdrawal	Elimination of U.S. product revenue
2011 onward	No meaningful U.S. commercial recovery	Residual or zero U.S. revenue

There was no commercially relevant period in which an unexpired formulation patent protected Darvon-N from generic competition. The primary intellectual-property risk was therefore generic price competition, while the decisive event was regulatory withdrawal.

What FDA regulatory action ended the U.S. market?

The FDA requested withdrawal of all propoxyphene products from the U.S. market on November 19, 2010. The action followed evidence that propoxyphene could cause clinically significant changes in cardiac electrical activity, including QT-interval prolongation, even at therapeutic doses. The FDA concluded that the safety risks outweighed the limited benefits for pain treatment. [1]

The agency’s action applied to:

Darvon-N;
Darvon;
Darvocet-N;
generic propoxyphene napsylate products;
generic propoxyphene hydrochloride products; and
combinations containing propoxyphene and acetaminophen.

Xanodyne agreed to withdraw its products, and generic manufacturers also discontinued their products. The FDA advised patients and prescribers to stop using propoxyphene and move to alternative treatments under medical supervision. [1]

The FDA had previously required stronger warnings, including a boxed warning, after accumulating reports of overdose, respiratory depression and suicide risk. The 2010 action converted a declining product category into a closed U.S. market.

What is the Orange Book status of propoxyphene napsylate?

Propoxyphene napsylate has no active U.S. Orange Book commercial position comparable to a marketed reference product. The relevant products were withdrawn, and there is no current U.S. reference-product strategy supporting an ANDA launch.

The key Orange Book and abbreviated-approval implications are:

Issue	Assessment
Listed reference product	Historically listed products existed; current commercial relevance is absent
Active ingredient	Propoxyphene salt products were withdrawn
Paragraph IV opportunity	No commercially meaningful current launch pathway
New drug exclusivity	Expired
Patent-term extension	Not relevant to the current market
Formulation protection	No known commercially material unexpired protection
Generic launch risk	Regulatory prohibition and market withdrawal dominate patent risk

A Paragraph IV challenge would have little economic value because an applicant would face the FDA’s safety-based withdrawal history, limited prescriber demand and potential regulatory barriers. Patent clearance alone would not create a viable launch opportunity.

How strong is the patent estate for propoxyphene napsylate?

The patent estate is commercially weak and effectively exhausted. Original propoxyphene composition and salt patents are historical assets. Their terms expired long before the 2010 withdrawal. No current patent barrier is known to protect a commercially viable U.S. propoxyphene napsylate franchise.

Composition and salt patents

Propoxyphene was developed and commercialized in the mid-20th century. The relevant composition claims and salt-form protection belonged to the early branded-product era. Any remaining value would have depended on later formulation, manufacturing or method-of-use patents.

Formulation patents

Darvon-N and Darvocet-N were conventional oral dosage forms. There is no evidence that a long-lived extended-release delivery system or complex drug-device platform preserved market exclusivity. Conventional capsule and tablet formulations were vulnerable to generic substitution.

Method-of-use patents

Method-of-use patents could not offset the product’s declining clinical position. The core indication, oral analgesia, was broad and mature. Later safety restrictions narrowed rather than expanded the practical value of any use claims.

Manufacturing and trade-secret barriers

Propoxyphene napsylate is a small-molecule salt, not a biologic. Manufacturing does not present the cell-line, comparability or process-characterization barriers associated with monoclonal antibodies. The active ingredient and conventional dosage forms were technically accessible to generic manufacturers.

What caused the financial decline of propoxyphene napsylate?

The financial trajectory followed a standard mature-drug erosion pattern until safety regulation abruptly ended the U.S. market.

Generic price erosion

Once generic propoxyphene products became available, branded Darvon-N revenue faced substitution and lower net pricing. Pharmacy benefit managers and insurers had little reason to preserve branded share for an old opioid without a meaningful patent barrier.

Clinical substitution

Propoxyphene competed with acetaminophen, nonsteroidal anti-inflammatory drugs, tramadol, codeine combinations and stronger opioid analgesics. Physicians increasingly viewed propoxyphene as an older product with limited efficacy and an unfavorable safety profile.

Safety-related demand destruction

Propoxyphene’s narrow therapeutic margin was a central commercial liability. Overdose could produce respiratory depression, and cardiac toxicity created risk that was not captured by ordinary opioid safety counseling. FDA warnings reduced new prescribing and encouraged discontinuation among existing users.

Geographic contraction

The product’s commercial footprint contracted before the U.S. withdrawal. The United Kingdom removed co-propoxyphene products after the Medicines and Healthcare products Regulatory Agency concluded that overdose risk outweighed benefits. The European Medicines Agency later recommended withdrawal of dextropropoxyphene-containing medicines across the European Union. [2,3]

U.S. withdrawal

The 2010 FDA action removed the largest remaining commercial market. For a mature product with generic competition and declining prescriptions, withdrawal eliminated the principal source of residual franchise value.

What were the revenues and financial exposure?

Public company filings and FDA materials do not provide a consistent standalone revenue series for propoxyphene napsylate. Available commercial data generally aggregate Darvon, Darvocet, generic products or broader company portfolios. A defensible product-specific revenue estimate cannot be derived from public regulatory records alone.

The financial exposure can still be assessed directionally:

Revenue driver	Pre-withdrawal position	Post-2010 position
U.S. branded sales	Declining and exposed to generics	Eliminated
U.S. generic sales	Price-competitive but volume-supported	Discontinued
European sales	Reduced by national withdrawals	Effectively eliminated
Pricing power	Low	None
Patent contribution	Minimal	None
Regulatory liability	Increasing	Product no longer marketed
Licensing value	Limited	Negligible for ordinary analgesic use

The product’s residual value was likely concentrated in existing distribution, brand recognition and manufacturing know-how. Those assets had little transferable value after the FDA concluded that the benefit-risk balance was unacceptable.

Which companies challenged or competed with propoxyphene napsylate?

The relevant competitive pressure came from substitute analgesics and generic manufacturers rather than from a single branded challenger.

Generic manufacturers

Generic companies competed on price after patent expiry. Their participation reduced branded revenue and made the product more dependent on prescription volume. Once FDA withdrawal occurred, the generic market also ended in the United States.

Therapeutic substitutes

The main commercial substitutes included:

tramadol;
acetaminophen;
ibuprofen and other NSAIDs;
codeine-acetaminophen combinations;
hydrocodone-acetaminophen products;
oxycodone-based products; and
nonpharmacologic pain-management approaches.

Tramadol was an important competitive alternative because it was positioned for moderate pain and was generally perceived as having a more favorable safety profile before later opioid-related controls and warnings.

Brand owners

Eli Lilly was historically associated with the original Darvon franchise. Xanodyne later held and marketed U.S. Darvon and Darvocet rights. After withdrawal, neither company retained a viable U.S. propoxyphene franchise.

What patent litigation or settlement agreements affected the product?

No ongoing patent litigation or settlement structure has material commercial significance for propoxyphene napsylate. The relevant patents were old, generic competition was established, and the U.S. product category was withdrawn on safety grounds.

This differs from modern pharmaceutical launches, where patent settlements can delay generic entry for years. Propoxyphene’s commercial outcome was determined by:

expiration of historical patents;
generic substitution;
safety warnings;
international withdrawal decisions; and
final FDA market withdrawal.

No biosimilar litigation applies because propoxyphene napsylate is a small-molecule drug, not a biologic.

What generic launch risks exist for propoxyphene napsylate?

A new generic launch would face risks that are primarily regulatory and commercial rather than patent-based.

Regulatory risk

The FDA’s withdrawal decision was based on the active ingredient’s safety profile. A new applicant would not simply need to demonstrate pharmaceutical equivalence. It would face the practical problem that the FDA had determined that propoxyphene’s risks outweighed its benefits.

Liability risk

Propoxyphene was associated with overdose deaths, respiratory depression and cardiac toxicity. Product-liability exposure would be disproportionate to the likely revenue opportunity.

Market risk

Prescriber demand is minimal or absent in the United States. Payers would have no reason to promote a withdrawn opioid when alternative analgesics are available.

Manufacturing risk

Manufacturing is technically manageable for a conventional small-molecule salt. The obstacle is not production complexity. It is the absence of a viable legal and commercial market.

How does propoxyphene napsylate compare with tramadol and other analgesics?

Criterion	Propoxyphene napsylate	Tramadol	Acetaminophen/NSAIDs
Current U.S. marketing	Withdrawn	Marketed	Marketed
Patent position	Historical patents expired	Product-specific patents generally expired or limited	Generally mature
Cardiac-risk concern	Material	Different safety profile, with seizure and serotonin risks	Different hepatic or gastrointestinal risks
Generic availability	Withdrawn category	Available	Widely available
Commercial growth	None	Mature market	Mature market
Biosimilar exposure	None	None	None
Launch attractiveness	Very low	Moderate only for selected formulations or combinations	Low for basic products

Propoxyphene’s competitive failure was not caused solely by cheaper alternatives. It lost its position because its efficacy was limited relative to available treatments while its overdose and cardiac risks remained consequential.

What is the current market outlook and revenue trajectory?

The current outlook is effectively zero for the U.S. and European branded markets. Propoxyphene napsylate has no credible growth path based on ordinary analgesic use, reformulation or generic relaunch.

A potential relaunch would require a new regulatory case addressing the historical safety findings. A standard abbreviated generic application would not solve the core problem. Any commercial development would likely require a new formulation, a restricted-use strategy or a different clinical indication, each carrying high regulatory, liability and market-adoption risk.

The product therefore has:

no meaningful patent-driven pricing power;
no current U.S. Orange Book commercial opportunity;
no biosimilar pathway;
minimal licensing value;
no established revenue base;
high safety-related liability exposure; and
negligible probability of a conventional generic revival.

Key Takeaways

Propoxyphene napsylate is a discontinued opioid analgesic, historically sold as Darvon-N and in Darvocet-N combinations.
U.S. products were withdrawn in November 2010 after FDA determined that cardiac risks outweighed analgesic benefits.
Original patents expired decades ago, and generic competition had already eroded pricing power.
No active patent estate, formulation strategy or method-of-use program provides meaningful current protection.
No biosimilar risk applies because the product is a small molecule.
A new generic launch would face regulatory, liability and commercial barriers that exceed the value of the market opportunity.
Public disclosures do not provide a reliable standalone revenue history for propoxyphene napsylate.
The financial trajectory is best characterized as mature branded decline, generic commoditization, safety-driven contraction and eventual market exit.

FAQs About Propoxyphene Napsylate

Is propoxyphene napsylate still available in the United States?

No. The FDA requested withdrawal of all propoxyphene products from the U.S. market in 2010, including propoxyphene napsylate products.

Did propoxyphene napsylate have a patent-protected extended-release formulation?

No commercially important extended-release patent estate is associated with the withdrawn Darvon-N franchise. The marketed products were conventional oral dosage forms.

Can a company file a Paragraph IV ANDA for propoxyphene napsylate?

A patent challenge could theoretically address historical listings, but it would not create a practical U.S. launch opportunity because the active ingredient was withdrawn for safety reasons.

Was propoxyphene napsylate withdrawn because of opioid addiction risk?

The decisive FDA concern was the overall benefit-risk profile, including potentially fatal overdose, respiratory depression and cardiac electrophysiology effects. Addiction risk was part of the broader opioid-risk environment but was not the sole basis for withdrawal.

Does propoxyphene napsylate have residual licensing value outside the United States?

Residual value is limited. Some historical international markets may have had different withdrawal timing, but the product’s mature patent position, safety profile and weak clinical differentiation substantially reduce licensing attractiveness.

References

U.S. Food and Drug Administration. (2010, November 19). FDA recommends against the continued use of propoxyphene. https://www.fda.gov
European Medicines Agency. (2009). European Medicines Agency recommends withdrawal of dextropropoxyphene-containing medicines. https://www.ema.europa.eu
Medicines and Healthcare products Regulatory Agency. (2007). Withdrawal of co-proxamol products. https://www.gov.uk
U.S. Food and Drug Administration. (2011). Propoxyphene: withdrawal and safety information. https://www.fda.gov
Drug Enforcement Administration. (2010). Controlled substances schedules and propoxyphene regulatory status. https://www.deadiversion.usdoj.gov

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