DARVON-N W/ ASA Drug Patent Profile

When do Darvon-n W/ Asa patents expire, and what generic alternatives are available?

Darvon-n W/ Asa is a drug marketed by Aaipharma Llc and is included in two NDAs.

The generic ingredient in DARVON-N W/ ASA is aspirin; propoxyphene napsylate. There is one drug master file entry for this compound. Additional details are available on the aspirin; propoxyphene napsylate profile page.

Summary for DARVON-N W/ ASA

US Patents:	0
Applicants:	1
NDAs:	2
DailyMed Link:	DARVON-N W/ ASA at DailyMed

US Patents and Regulatory Information for DARVON-N W/ ASA

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Aaipharma Llc	DARVON-N W/ ASA	aspirin; propoxyphene napsylate	CAPSULE;ORAL	016829-001	Approved Prior to Jan 1, 1982		DISCN	No	No
Aaipharma Llc	DARVON-N W/ ASA	aspirin; propoxyphene napsylate	TABLET;ORAL	016863-001	Approved Prior to Jan 1, 1982		DISCN	No	No

DARVON-N W/ ASA Market Dynamics, Patent Status, FDA Withdrawal, and Financial Trajectory

Last updated: August 8, 2026

DARVON-N W/ ASA was a legacy propoxyphene-and-aspirin analgesic product that lost commercial viability after the FDA concluded that propoxyphene created a serious risk of cardiac toxicity. The FDA requested withdrawal of all propoxyphene products from the U.S. market in November 2010. DARVON-N W/ ASA has no meaningful current U.S. revenue base, no active U.S. exclusivity position, and no credible generic-launch opportunity under the original product name. Its remaining commercial significance is historical, regulatory, and litigation-related rather than operational. [1]

What was DARVON-N W/ ASA?

DARVON-N W/ ASA combined propoxyphene napsylate, an opioid analgesic, with aspirin, or ASA. The product was part of the Darvon family of prescription pain medicines marketed for mild to moderate pain.

Propoxyphene products were sold in multiple formulations, including:

Product family	Active pharmaceutical ingredient	Combination partner	Commercial status
Darvon	Propoxyphene	None	Withdrawn in the U.S.
Darvon-N	Propoxyphene napsylate	None	Withdrawn in the U.S.
Darvon-N W/ ASA	Propoxyphene napsylate	Aspirin	Withdrawn or discontinued in the U.S.
Darvocet-N	Propoxyphene napsylate	Acetaminophen	Withdrawn in the U.S.
Darvon Compound-65	Propoxyphene hydrochloride	Acetaminophen	Withdrawn in the U.S.

The “N” designation generally referred to propoxyphene napsylate rather than propoxyphene hydrochloride. Aspirin was used as the non-opioid analgesic component in the combination product.

When did DARVON-N W/ ASA lose exclusivity?

DARVON-N W/ ASA lost practical exclusivity decades before the FDA withdrawal. The product was based on an old small-molecule opioid and aspirin combination, not a recently developed chemical entity or modern drug-delivery system.

Patent timeline

Event	Approximate timing	Commercial impact
Propoxyphene development and early patenting	1950s	Established the original opioid franchise
U.S. marketing of propoxyphene products	1950s onward	Created a long-lived legacy analgesic franchise
Core compound and formulation patent terms	Primarily expired by the late 20th century	Removed meaningful patent-based exclusivity
Generic propoxyphene competition	Before 2010	Reduced branded pricing power
FDA withdrawal request	November 2010	Ended U.S. commercial availability
Current status	No active U.S. commercial market	No current product-level revenue opportunity

No active U.S. composition-of-matter or formulation patent appears to provide market protection for DARVON-N W/ ASA today. Any original patents would have expired long before the 2010 withdrawal. Patent protection therefore did not drive the product’s termination.

What was the FDA regulatory status of DARVON-N W/ ASA?

The FDA removed propoxyphene products from the U.S. market after reviewing new safety data showing dose-related cardiac electrophysiologic effects, including QT-interval prolongation, QRS widening, and PR-interval prolongation.

In July 2009, the FDA required stronger warnings and additional risk controls for propoxyphene products. In November 2010, after concluding that the cardiac risks outweighed the modest benefits for pain treatment, the agency requested that manufacturers voluntarily withdraw propoxyphene products. [1]

The FDA’s action applied to the propoxyphene class, including products containing:

• Propoxyphene alone
• Propoxyphene with acetaminophen
• Propoxyphene with aspirin

The FDA advised patients and prescribers to transition to alternative pain treatments rather than discontinue therapy without medical supervision. [1]

Orange Book status

DARVON-N W/ ASA does not have a meaningful current Orange Book position. Its commercial listing, if present in historical or discontinued-product records, does not create an active reference-product market. The relevant FDA status is discontinued or withdrawn, not an active branded product with remaining exclusivity.

The withdrawal was based on safety and benefit-risk concerns, not on patent expiration alone.

What patents protected DARVON-N W/ ASA?

The product historically could have been supported by several categories of intellectual property:

1. Propoxyphene compound patents.
2. Propoxyphene napsylate salt patents.
3. Combination-product patents covering propoxyphene and aspirin.
4. Tablet formulation or manufacturing patents.
5. Brand and trademark rights covering the Darvon name.

Those rights do not create a current commercial barrier. The compound was introduced in the 1950s, and any ordinary U.S. patent term associated with the original active ingredient expired many years ago. Modern U.S. patent terms generally run 20 years from the relevant non-provisional filing date, subject to historical rules and adjustments. [2]

What formulations were protected?

The aspirin combination may historically have been differentiated through tablet composition, dosage ratios, manufacturing specifications, and branding. Those distinctions did not produce durable exclusivity in the current market.

No known active formulation patent gives a sponsor a basis to relaunch DARVON-N W/ ASA as an FDA-protected branded product. A new sponsor would need to address:

• Propoxyphene’s cardiac safety profile
• Controlled-substance requirements
• A new FDA benefit-risk assessment
• Clinical and pharmacokinetic data
• Manufacturing controls
• Labeling and post-market surveillance
• Potential competition from safer analgesics

A legacy formulation patent would not solve those regulatory problems.

How did the FDA withdrawal change the market?

The withdrawal eliminated the U.S. propoxyphene market rather than shifting share from the branded product to generic equivalents. Patients and prescribers moved toward other analgesic classes, including:

• Acetaminophen
• Nonsteroidal anti-inflammatory drugs
• Tramadol
• Hydrocodone combinations
• Oxycodone combinations
• Other opioid and non-opioid therapies

The market effect was a class exit. Generic manufacturers did not have an incentive to launch or maintain supply after the reference products were withdrawn for safety reasons.

Generic entry risk

Current generic-entry risk is effectively zero in the conventional commercial sense. There is no attractive active reference-product market to attack, and a generic manufacturer would face the same cardiac-safety concerns associated with propoxyphene.

A potential ANDA applicant would also face practical difficulties:

• The reference product is no longer commercially active.
• FDA withdrawal was linked to safety, not simply weak demand.
• Substitution would require prescriber acceptance of a withdrawn opioid.
• Controlled-substance distribution carries additional compliance costs.
• Alternative analgesics are widely available.

The principal risk is therefore not generic erosion. It is regulatory inability to commercialize the molecule.

Which companies marketed or controlled DARVON-N W/ ASA?

The Darvon franchise was historically associated with Eli Lilly and Company. Xanodyne Pharmaceuticals later acquired rights to several propoxyphene products and became the principal U.S. sponsor associated with the products at the time of the FDA withdrawal. [1]

The relevant commercial structure changed over time:

Period	Commercial position
Early development and legacy branding	Eli Lilly-associated Darvon franchise
Later U.S. commercialization	Xanodyne Pharmaceuticals
After FDA withdrawal	No active U.S. sponsor-led market
Current position	Historical asset with no meaningful marketed-product value

A specific revenue stream for DARVON-N W/ ASA has not been publicly disclosed in a way that supports a reliable standalone financial series. Product-level sales were generally reported within broader company portfolios, and the aspirin combination was not the principal publicly tracked driver of the Darvon franchise.

What was the financial trajectory of DARVON-N W/ ASA?

The financial trajectory followed four stages.

1. Mature branded growth

The product benefited from the established Darvon brand, physician familiarity, and the prescription analgesic market. Its commercial position was strongest before broad generic competition and before modern concerns about opioid safety became central to prescribing decisions.

2. Generic and therapeutic erosion

The product’s economic position weakened as:

• Propoxyphene patents expired.
• Generic propoxyphene products entered the market.
• Physicians gained access to alternative analgesics.
• Payers reduced incentives for older branded products.
• Opioid safety scrutiny increased.

The aspirin combination had limited differentiation because aspirin was widely available and did not create a durable barrier to substitution.

3. Regulatory collapse

The 2010 FDA withdrawal ended U.S. sales. Revenue did not merely decline through ordinary product maturity. It was effectively terminated by a regulatory decision affecting the active ingredient. [1]

4. Post-withdrawal financial exposure

After withdrawal, the economic issues shifted from product sales to liabilities and remediation. Relevant exposures included:

• Product-liability litigation
• Recall and inventory costs
• Regulatory compliance
• Patient communications
• Insurance claims
• Legal defense
• Potential settlement costs
• Brand impairment

For a company holding the product rights, the asset’s value after 2010 was likely negative or negligible on a risk-adjusted basis unless litigation reserves and liabilities had been resolved.

What patent litigation affected DARVON-N W/ ASA?

There is no current patent litigation of commercial significance involving DARVON-N W/ ASA. The product’s principal legal exposure arose from safety and product-liability claims rather than patent enforcement.

The withdrawal of propoxyphene products generated multidistrict and state-court litigation involving alleged cardiac injury, overdose, dependence, and inadequate warnings. Those proceedings affected the broader Darvon, Darvocet, and propoxyphene product group rather than creating a patent-based market dispute.

The legal distinction is important:

Legal issue	Relevance to DARVON-N W/ ASA
Patent infringement	Low or obsolete
Paragraph IV challenge	No current commercial significance
Orange Book patent dispute	No active strategic relevance
Product liability	Material historical exposure
FDA enforcement and withdrawal	Principal regulatory event
Settlement activity	Case-specific and historical

Were there Paragraph IV challenges to DARVON-N W/ ASA?

Paragraph IV litigation is not a meaningful current issue for DARVON-N W/ ASA. Paragraph IV challenges typically target active branded reference products with commercial sales, listed patents, and a viable generic launch opportunity.

DARVON-N W/ ASA lacks those conditions. Its original patent estate is expired, its product is withdrawn, and the active ingredient carries a regulatory safety problem. Any historical generic filings would not create a current launch pathway.

Does DARVON-N W/ ASA have biosimilar risk?

No. DARVON-N W/ ASA is a conventional small-molecule drug, not a biologic. Biosimilar rules do not apply.

The relevant competitive categories are generic drugs and therapeutic substitutes. In practice, the principal commercial replacement products were other analgesics, not biosimilars or follow-on biologics.

How strong was the patent estate for DARVON-N W/ ASA?

The historical patent estate was commercially useful during the early life of the propoxyphene franchise but is now exhausted.

Patent-estate factor	Assessment
Core molecule	Expired
Salt form	Expired or commercially irrelevant
Aspirin combination	Limited differentiation; no current barrier
Tablet formulation	No current market protection identified
Manufacturing know-how	Not sufficient to overcome regulatory withdrawal
Trademark	Historical brand value only
Exclusivity strength today	None

The strongest residual protection was brand recognition, not patent rights. Brand recognition has no practical value when FDA safety action prevents continued marketing.

What is the international market status?

Propoxyphene faced regulatory action outside the United States as well. The European Commission recommended withdrawal of propoxyphene-containing medicines in 2009 after concerns that the risks outweighed the benefits. [3]

The international market therefore contracted in parallel with the U.S. market. Country-specific withdrawal timing, product names, and legal statuses varied, but the molecule’s global commercial trajectory was negative. Geographic expansion was not a credible strategy after the safety findings.

What is the relaunch or licensing outlook?

A conventional licensing transaction for DARVON-N W/ ASA is unlikely to have meaningful value. A licensee would receive an old, unprotected molecule with:

• No effective patent exclusivity
• No active U.S. market
• A serious cardiac safety history
• Product-liability exposure
• Limited clinical differentiation
• Strong competition from alternative analgesics

A relaunch would require a new regulatory strategy and substantial evidence to establish a favorable benefit-risk profile. The commercial case would be weak even if regulatory approval were theoretically obtainable.

Key Takeaways

• DARVON-N W/ ASA was a propoxyphene napsylate and aspirin prescription analgesic.
• The FDA requested withdrawal of all propoxyphene products from the U.S. market in November 2010 because of cardiac safety risks.
• Original patents and any meaningful formulation exclusivity expired long before the withdrawal.
• DARVON-N W/ ASA has no current U.S. commercial revenue base or meaningful Orange Book exclusivity.
• Generic-entry risk is effectively immaterial because the reference product is withdrawn and the active ingredient has an unfavorable regulatory profile.
• The relevant historical liabilities are product-liability litigation and withdrawal-related costs, not patent infringement.
• The product is not subject to biosimilar competition because it is a small-molecule drug.
• Any remaining asset value is historical or litigation-related rather than tied to future sales.

FAQs

Is DARVON-N W/ ASA still available by prescription?

No. Propoxyphene products, including Darvon-family products, were withdrawn from the U.S. market following the FDA’s November 2010 action.

What was the difference between DARVON-N W/ ASA and Darvocet-N?

DARVON-N W/ ASA combined propoxyphene napsylate with aspirin. Darvocet-N combined propoxyphene napsylate with acetaminophen.

Can a company launch a generic version of DARVON-N W/ ASA?

A theoretical regulatory filing is different from a commercially viable launch. The product’s withdrawal, cardiac safety concerns, lack of meaningful patent protection, and weak clinical positioning make a conventional generic launch commercially unattractive.

Did aspirin provide additional patent protection for DARVON-N W/ ASA?

Aspirin may have supported historical combination-product claims, but it did not create durable current exclusivity. Aspirin is an old, widely available active ingredient, and any historical combination patents would have expired.

Was DARVON-N W/ ASA involved in opioid litigation?

The broader propoxyphene product group was involved in product-liability claims and related litigation. Those claims focused on alleged injury, cardiac risk, warnings, and withdrawal issues rather than current patent enforcement.

References

1. U.S. Food and Drug Administration. (2010, November 19). FDA recommends against the continued use of propoxyphene. https://www.fda.gov
2. United States Patent and Trademark Office. (n.d.). Patent term adjustment and patent term information. https://www.uspto.gov
3. European Medicines Agency. (2009, June 25). European Medicines Agency recommends withdrawal of dextropropoxyphene-containing medicines. https://www.ema.europa.eu