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Acetaminophen; propoxyphene napsylate - Generic Drug Details
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What are the generic drug sources for acetaminophen; propoxyphene napsylate and what is the scope of patent protection?
Acetaminophen; propoxyphene napsylate
is the generic ingredient in five branded drugs marketed by Xanodyne Pharm, Teva, Able, Actavis Elizabeth, Cornerstone, Halsey, Ivax Sub Teva Pharms, Mallinckrodt, Mirror Pharms, Mutual Pharm, Mylan, Mylan Pharms Inc, Sandoz, Superpharm, Vintage Pharms, Watson Labs, Watson Labs Florida, and Wockhardt Ltd, and is included in twenty-nine NDAs. Additional information is available in the individual branded drug profile pages.Summary for acetaminophen; propoxyphene napsylate
| US Patents: | 0 |
| Tradenames: | 5 |
| Applicants: | 18 |
| NDAs: | 29 |
| DailyMed Link: | acetaminophen; propoxyphene napsylate at DailyMed |
US Patents and Regulatory Information for acetaminophen; propoxyphene napsylate
Acetaminophen and Propoxyphene Napsylate: Market Dynamics, Patent Status, and Financial Trajectory
Acetaminophen remains a high-volume, low-cost analgesic sold globally in prescription and over-the-counter products. Propoxyphene napsylate has no legitimate U.S. commercial market after the FDA withdrew propoxyphene products in 2010 because of dose-related cardiac toxicity. The fixed-dose combination, historically marketed as Darvocet-N, has no meaningful remaining patent, regulatory, or commercial value in the United States.
What was the acetaminophen and propoxyphene napsylate product?
The relevant product was a prescription combination of acetaminophen and propoxyphene napsylate, an opioid analgesic. Products were marketed primarily under the Darvocet and Darvocet-N brands.
| Product | Active ingredients | Historical use | U.S. regulatory status |
|---|---|---|---|
| Darvocet-N 50 | Propoxyphene napsylate 50 mg and acetaminophen 325 mg | Mild to moderate pain | Withdrawn |
| Darvocet-N 100 | Propoxyphene napsylate 100 mg and acetaminophen 650 mg | Mild to moderate pain | Withdrawn |
| Darvon-N | Propoxyphene napsylate without acetaminophen | Pain treatment | Withdrawn |
| Generic propoxyphene-acetaminophen products | Propoxyphene plus acetaminophen, varying strengths | Pain treatment | Withdrawn |
Propoxyphene was an opioid with limited analgesic effectiveness and a narrow safety margin. The active ingredient was associated with QT-interval prolongation, widened QRS complexes, ventricular arrhythmias, and sudden death, including at therapeutic doses. Acetaminophen added a separate risk of hepatotoxicity when total daily exposure exceeded recommended limits or when combined with other acetaminophen-containing products.
The FDA requested voluntary withdrawal of propoxyphene products from the U.S. market in November 2010. The agency concluded that the cardiac risks outweighed the modest pain-relief benefit.[1]
When did propoxyphene lose U.S. market exclusivity?
Propoxyphene and acetaminophen lost meaningful U.S. market exclusivity decades before the 2010 withdrawal. The products were established prescription medicines during the second half of the 20th century, and generic versions were available long before the FDA action.
The commercially relevant sequence was:
| Period | Market event |
|---|---|
| 1950s-1960s | Propoxyphene products introduced and commercialized |
| 1970s-1990s | Brand and generic propoxyphene-acetaminophen products sold in the U.S. |
| 2000s | Safety concerns increased; sales declined as safer alternatives gained share |
| July 2009 | FDA required stronger safety labeling and medication guidance |
| November 2010 | FDA requested withdrawal of all propoxyphene products |
| 2011 | U.S. commercial availability ended after product removal |
Any original composition, formulation, or manufacturing patents covering the combination would have expired before the modern withdrawal period. Patent term extension and pediatric exclusivity were not commercially relevant to the product’s final U.S. market status.
What is the Orange Book status of propoxyphene-acetaminophen?
There is no active U.S. Orange Book commercial position supporting a current propoxyphene-acetaminophen market. The FDA’s withdrawal action removed the underlying products from U.S. distribution, and the product’s old patent and exclusivity framework no longer creates a launch barrier.
The Orange Book implications are:
- No current U.S. reference product supports a normal abbreviated new drug application launch.
- No commercially relevant unexpired listed patent protects the historical combination.
- Paragraph IV litigation is not an active competitive issue.
- A company seeking to sell the product would face a regulatory safety barrier, not a conventional patent barrier.
- Reintroduction would require a new regulatory strategy and evidence addressing the cardiac safety concerns that led to withdrawal.
The legal distinction matters. A drug can have expired patents and still be commercially unavailable because the FDA has withdrawn the product for safety reasons.
What patents protect acetaminophen and propoxyphene napsylate?
The active ingredients are effectively off-patent.
Acetaminophen patent position
Acetaminophen, also known as paracetamol, has been used clinically for many decades. Core composition-of-matter protection has expired. Current commercial value is concentrated in:
- Brand recognition
- Retail distribution
- Product quality
- Dosage-form convenience
- Combination-product positioning
- Manufacturing cost
- Regulatory compliance
Some acetaminophen products can have later patents covering specific delivery systems, liquid formulations, extended-release designs, abuse-deterrent features, or combinations. Those patents do not restore exclusivity to the active ingredient itself.
Propoxyphene patent position
Propoxyphene napsylate is also an old active ingredient with expired core patent protection. Any historical patents covering the molecule, salt form, formulation, or combination with acetaminophen would generally have expired long before the U.S. withdrawal.
No current patent estate creates a credible barrier to a generic version of the historical product. The principal barrier is the FDA’s unfavorable benefit-risk assessment.
Combination-product patent position
The acetaminophen-propoxyphene combination was protected historically through product approvals, trademarks, formulation know-how, and potentially combination or dosage-form patents. Those rights no longer support a viable U.S. franchise.
The remaining intellectual-property value is limited to:
- Historical trademarks such as Darvocet
- Archived regulatory data
- Manufacturing records
- Brand history
- Potential rights in jurisdictions where legacy products were treated differently
These assets do not compensate for the U.S. withdrawal.
What was the financial trajectory of the product?
The product’s financial trajectory followed a classic transition from mature opioid franchise to regulatory collapse.
Growth and maturity
Darvocet and related propoxyphene products benefited from several commercial advantages:
- Established physician familiarity
- Low-cost oral dosing
- Broad use for mild or moderate pain
- Availability in a fixed-dose acetaminophen combination
- Long-standing brand recognition
The product competed successfully during a period when opioid safety standards were less restrictive and alternatives were more limited.
Decline
Sales deteriorated as evidence accumulated regarding overdose, accidental exposure, drug interactions, and cardiac toxicity. Physicians increasingly shifted prescribing toward other options, including nonsteroidal anti-inflammatory drugs, tramadol, hydrocodone-acetaminophen, oxycodone-acetaminophen, and nonopioid analgesics.
The commercial decline was driven by:
- Safety-label changes.
- Increased scrutiny of opioid prescribing.
- Generic price erosion.
- Competition from newer analgesics.
- Liability and compliance costs.
- FDA withdrawal.
Public filings do not provide a consistently reported, standalone global revenue series for acetaminophen-propoxyphene products across all manufacturers and generic suppliers. The product-level revenue base had already become immaterial relative to the broader acetaminophen market by the time of withdrawal.
How does propoxyphene compare with acetaminophen commercially?
The two ingredients have completely different market trajectories.
| Metric | Acetaminophen | Propoxyphene napsylate |
|---|---|---|
| Current U.S. status | Widely marketed | Withdrawn |
| Market type | OTC and prescription | Historical prescription opioid |
| Patent position | Core patents expired; product-level innovation possible | Core patents expired |
| Current revenue base | Large global consumer-health market | Effectively zero in legitimate U.S. sales |
| Regulatory risk | Dose-related liver toxicity | Cardiac toxicity plus opioid risks |
| Generic competition | Intense | Commercially irrelevant after withdrawal |
| Biosimilar exposure | None | None |
| Commercial outlook | Stable to growing in selected formats | No U.S. recovery absent major regulatory reversal |
Acetaminophen remains one of the most widely used analgesic ingredients worldwide. Its market includes tablets, capsules, liquids, powders, suppositories, intravenous formulations, and combination products. Propoxyphene napsylate has no comparable current market.
Which companies challenged or replaced the product?
No active Paragraph IV challenge is commercially material because the product was withdrawn rather than displaced through ordinary generic competition. Generic manufacturers historically included multiple companies selling propoxyphene-acetaminophen products, but those products were removed after the FDA action.
The competitive replacement set included:
- Tramadol products
- Hydrocodone-acetaminophen products
- Codeine-acetaminophen products
- Oxycodone-acetaminophen products
- Nonsteroidal anti-inflammatory drugs
- Acetaminophen monotherapy
- Topical analgesics
- Nonpharmacologic pain-management approaches
The closest replacement depended on pain severity, patient risk, opioid controls, and prescriber preference. Tramadol and hydrocodone combinations captured some prescription demand, while acetaminophen and ibuprofen captured lower-acuity pain demand.
What litigation and settlement agreements affected propoxyphene?
The most important legal event was regulatory rather than patent-based: FDA-ordered market withdrawal in 2010. The agency relied on new safety data and a quantitative risk-benefit assessment showing that propoxyphene produced clinically important cardiac electrophysiology changes.[1]
Historical legal exposure also involved:
- Wrongful-death claims
- Product-liability claims
- Allegations concerning overdose and cardiac events
- Failure-to-warn theories
- Controlled-substance compliance
- Manufacturer and distributor responsibilities
The principal U.S. manufacturer at the time of withdrawal was Xanodyne Pharmaceuticals, which marketed propoxyphene products after acquiring relevant rights. Eli Lilly was the original developer and historical marketer of Darvon and Darvocet products. The withdrawal ended ordinary commercial competition but did not eliminate potential product-liability exposure.
No broadly material, current patent settlement controls generic entry because the product is no longer an active U.S. market.
What generic launch risks exist?
A conventional generic launch is commercially unattractive and legally complex.
U.S. launch scenario
A company attempting to launch propoxyphene-acetaminophen in the U.S. would face:
- No viable ordinary market following withdrawal.
- FDA safety concerns that caused the original product to leave commerce.
- Potential need for a new drug application or a regulatory pathway materially different from a standard generic filing.
- Product-liability exposure.
- Controlled-substance compliance requirements.
- Limited physician demand.
- High insurance and distribution friction.
Expired patents would not solve these problems.
International launch scenario
Some countries historically retained propoxyphene products after the U.S. withdrawal, while others restricted or removed them. International opportunity would depend on each country’s national regulator, local pharmacovigilance findings, controlled-substance rules, and product-registration history.
Geographic variation does not establish a durable commercial opportunity. Propoxyphene’s safety profile has led to broad restrictions, and global demand has shifted toward other analgesics.
Are there formulation patents or manufacturing barriers?
No formulation patent is likely to create a meaningful current barrier for the historical combination. Manufacturing itself is technically straightforward compared with complex biologics, sterile injectables, or advanced drug-delivery systems.
The practical barriers are regulatory and operational:
- Qualified active-pharmaceutical-ingredient supply
- Controlled-substance handling
- Validated manufacturing processes
- Acetaminophen content uniformity
- Stability and impurity control
- Pharmacovigilance
- Product-liability insurance
- Distribution controls
- Regulatory review of cardiac risk
For acetaminophen alone, manufacturing competition is intense. Scale, procurement, quality systems, and retail access determine economics more than patents.
What is the biosimilar risk?
There is no biosimilar risk. Acetaminophen and propoxyphene napsylate are small-molecule drugs, not biologics. Competition occurs through generic-drug pathways, product approvals, manufacturing economics, and regulatory controls.
The relevant distinction is:
- Acetaminophen: substantial generic and private-label competition.
- Historical propoxyphene-acetaminophen: generic competition existed, but the market ended through withdrawal.
- Biosimilar competition: not applicable.
How strong is the patent estate?
The patent estate is commercially weak to nonexistent for the historical combination.
| Patent-estate category | Acetaminophen | Propoxyphene-acetaminophen |
|---|---|---|
| Core molecule protection | Expired | Expired |
| Historical formulation protection | Expired or immaterial | Expired or immaterial |
| Active Orange Book barrier | None of commercial significance | None of commercial significance |
| Method-of-use protection | Limited current value | No meaningful current value |
| Manufacturing know-how | Commodity-scale advantage only | Possible operational value, not exclusivity |
| Trademark value | Brand-dependent | Historical only |
| Litigation leverage | Low for legacy product | Low, with regulatory risk dominant |
Any surviving patents in narrow acetaminophen delivery systems would protect those specific products, not propoxyphene or the withdrawn combination.
What is the financial outlook?
The outlook divides into two separate businesses.
Acetaminophen has durable revenue potential because it is inexpensive, familiar, widely distributed, and available across multiple dosage forms. Growth is likely to come from premium formulations, pediatric and geriatric formats, combination products, international expansion, and hospital use rather than from core-molecule exclusivity.
Propoxyphene napsylate has no meaningful U.S. revenue outlook. A return would require regulators to accept a substantially different safety profile or risk-control framework, an unlikely outcome given the FDA’s withdrawal rationale and the availability of alternative analgesics.
Key Takeaways
- Acetaminophen is a large, mature, off-patent analgesic market with continuing commercial value.
- Propoxyphene napsylate is a withdrawn opioid with no legitimate U.S. market.
- Darvocet-N and related products were removed after FDA-identified cardiac risks outweighed their analgesic benefit.
- Core patents and historical exclusivity for both ingredients expired long ago.
- No active Paragraph IV dispute or Orange Book patent barrier drives the current competitive landscape.
- Generic launch risk is dominated by FDA safety and liability concerns, not intellectual property.
- Biosimilar analysis is irrelevant because both ingredients are small molecules.
- The historical combination has negligible current revenue exposure, while acetaminophen remains commercially significant.
FAQs About Acetaminophen and Propoxyphene Napsylate
Can propoxyphene-acetaminophen still be prescribed in the United States?
No. FDA-approved propoxyphene products were withdrawn from the U.S. market in 2010 because of cardiac safety risks.[1]
Was Darvocet-N a generic drug?
Darvocet-N was a branded prescription combination. Generic propoxyphene-acetaminophen products were also sold before the withdrawal.
Does acetaminophen still have active formulation patents?
Some specific acetaminophen products may have patents covering delivery systems, release profiles, combinations, or dosage forms. Those rights do not cover acetaminophen as a molecule.
Is propoxyphene a controlled substance?
Propoxyphene was federally controlled in the United States before market withdrawal. Its historical classification and controlled-substance requirements added compliance costs to manufacturing and distribution.
Could a company relaunch propoxyphene outside the United States?
A relaunch would depend on the regulator and country-specific product status. Prior approval or historical marketing in another jurisdiction would not eliminate the need to address current safety, pharmacovigilance, and controlled-substance requirements.
References
-
U.S. Food and Drug Administration. (2010, November 19). FDA recommends against the continued use of propoxyphene. https://www.fda.gov/drugs/drug-safety-and-availability/fda-recommends-against-continued-use-propoxyphene
-
U.S. Food and Drug Administration. (2009, July 7). FDA announces new safety labeling for propoxyphene products. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers
-
U.S. Food and Drug Administration. (2010). FDA briefing document: Cardiovascular safety concerns with propoxyphene. Center for Drug Evaluation and Research.
-
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/
-
U.S. Food and Drug Administration. (2011, March 1). FDA drug safety communication: Propoxyphene products withdrawn from the U.S. market. https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-propoxyphene-products-withdrawn-us-market
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