United States Patent 5,508,042: Scope, Claims, Expiration, and Oxycodone Patent Landscape
U.S. Patent No. 5,508,042 protected a pharmacokinetic method for treating pain with twice-daily controlled-release oxycodone. Its claims were directed to dose ranges, plasma concentration ranges, timing of peak and trough concentrations, and repeated administration through steady state. The patent did not broadly cover every oxycodone controlled-release tablet.
The patent was assigned to Purdue Pharma L.P. and formed part of the original OxyContin patent estate. Its practical exclusivity ended in 2013, subject to any applicable patent-term adjustment or pediatric extension. It is no longer a live barrier to generic oxycodone extended-release approval or launch. [1][2]
What does U.S. Patent 5,508,042 cover?
The patent covers a method of reducing variability in the daily oxycodone dose needed to control pain. The claimed method requires administration of an oral controlled-release oxycodone formulation that produces specified average plasma concentrations over a 12-hour dosing interval.
The claims combine four technical elements:
- A human pain-treatment method.
- Oral controlled-release oxycodone or an oxycodone salt.
- A defined dose range.
- Defined mean pharmacokinetic results after repeated every-12-hour dosing through steady state.
The patent therefore sits between a formulation patent and a method-of-use patent. It is not limited solely to tablet composition or excipient selection. Its central limitation is the pharmacokinetic performance of the administered product.
Patent identification
| Field |
Information |
| Patent |
U.S. Patent No. 5,508,042 |
| Title |
Controlled release oxycodone compositions |
| Assignee |
Purdue Pharma L.P. |
| Drug |
Oxycodone or an oxycodone salt |
| Dosage form |
Oral controlled-release formulation |
| Administration |
Repeated every 12 hours |
| Therapeutic use |
Pain control |
| Claim type |
Method of treatment with pharmacokinetic limitations |
| Issue date |
April 16, 1996 |
| Historical patent term |
Ended in 2013, subject to applicable term adjustments or extensions |
| Current status |
Expired; no current Orange Book exclusivity |
The patent’s claims are narrower than a claim covering oxycodone generally. Immediate-release oxycodone, non-oral products, once-daily products, and formulations that do not meet the specified pharmacokinetic limitations fall outside the literal scope of the claims.
How do claims 1 and 2 differ?
Claim 1 covers a lower dose range and tighter plasma concentration parameters. Claim 2 covers a substantially broader dose range but requires treatment of “substantially all human patients” and uses upper-bound pharmacokinetic limitations.
| Limitation |
Claim 1 |
Claim 2 |
| Oxycodone dose |
About 10 to about 40 mg |
About 10 to about 160 mg |
| Dosage form |
Oral controlled-release formulation |
Oral solid controlled-release formulation |
| Peak concentration |
Mean maximum plasma concentration about 6 to about 60 ng/mL |
Mean maximum concentration up to about 240 ng/mL |
| Peak timing |
Mean of about 2 to about 4.5 hours |
Mean of up to about 2 to about 4.5 hours |
| Trough concentration |
Mean minimum concentration about 3 to about 30 ng/mL |
Mean minimum concentration up to about 120 ng/mL |
| Trough timing |
Mean of about 10 to about 14 hours |
Mean of about 10 to about 14 hours |
| Dosing condition |
Repeated every 12 hours through steady state |
Repeated every 12 hours through steady state |
| Patient population |
Human patients |
Substantially all human patients |
What is the scope of claim 1?
Claim 1 requires all of the following:
- The patient is human.
- The method is intended to reduce the range of daily doses needed to control pain.
- The product is oral and controlled release.
- The product contains approximately 10 to 40 mg of oxycodone or a salt.
- Repeated dosing occurs every 12 hours.
- The patient has reached steady state.
- The mean maximum oxycodone concentration is approximately 6 to 60 ng/mL.
- The mean maximum occurs approximately 2 to 4.5 hours after dosing.
- The mean minimum concentration is approximately 3 to 30 ng/mL.
- The mean minimum occurs approximately 10 to 14 hours after dosing.
A product could satisfy the dose limitation but fail claim 1 if its mean peak concentration, trough concentration, or timing falls outside the stated ranges. The same result would apply if the product is dosed once daily or every eight hours rather than every 12 hours.
What is the scope of claim 2?
Claim 2 reaches doses up to approximately 160 mg and therefore covers higher-strength controlled-release oxycodone treatment than claim 1. It also expressly requires an oral solid dosage form and treatment of “substantially all human patients.”
Its broader dose range does not make the claim unrestricted. The formulation must still produce the claimed concentration profile after repeated 12-hour dosing at steady state. The phrase “up to about” creates an upper-bound limitation, while the timing language continues to constrain the pharmacokinetic profile.
Claim 2 is potentially broader in dose and concentration but potentially more demanding in patient-population proof. A generic product could avoid literal infringement if it failed the “substantially all” limitation, although such an avoidance strategy would depend on claim construction and the factual evidence concerning the product’s clinical performance.
What pharmacokinetic features did the patent protect?
The patent protected a relatively stable 12-hour exposure profile. The relevant relationship is not simply the amount of oxycodone in the tablet. It is the combination of:
- Peak exposure after dosing.
- Trough exposure before the next dose.
- The interval between those concentrations.
- Reproducibility at steady state.
- Reduced variability in the total daily dose needed to control pain.
The claims use mean concentrations rather than requiring every individual patient to remain within the stated range. This distinction matters. A product may produce individual patient values outside the claimed range while still meeting a claim expressed in terms of population means.
The claims also use approximate numerical ranges. Courts generally assess such language through claim construction, specification evidence, prosecution history, and the ordinary meaning of “about.” The word does not eliminate the numerical limitations.
What formulation patents competed with U.S. Patent 5,508,042?
The original OxyContin estate included patents directed to controlled-release oxycodone compositions, manufacturing approaches, and related pharmacokinetic properties. U.S. Patent No. 5,508,042 was part of that estate but did not independently cover every formulation attribute.
Other Purdue-related patents historically associated with OxyContin included the following:
| Patent |
General subject matter |
Strategic role |
| U.S. 5,508,042 |
Controlled-release oxycodone treatment and pharmacokinetic profile |
Method-of-use and PK protection |
| U.S. 5,549,912 |
Controlled-release oxycodone composition |
Formulation protection |
| U.S. 5,656,295 |
Controlled-release oxycodone composition or related delivery technology |
Formulation and release profile protection |
| Later OxyContin patents |
Abuse-deterrent formulation and manufacturing technology |
Lifecycle management and replacement protection |
The precise infringement analysis for the formulation patents depends on the asserted claims. A generic product might avoid the 5,508,042 method claims while still implicating a composition or manufacturing patent, or it might avoid all expired patents but face regulatory requirements unrelated to patent infringement.
When did U.S. Patent 5,508,042 lose exclusivity?
The patent’s enforceable term ended in 2013. Historical Orange Book listings for the original OxyContin patents placed the relevant protection in the 2013 period, with pediatric exclusivity potentially extending certain listed protection by six months. [2][3]
The patent is now expired. Its claims cannot support a new Paragraph IV litigation campaign, injunction, or automatic 30-month stay. Expiration also means that a generic applicant does not need to certify that it will wait for the patent to expire if the patent is no longer listed as an unexpired patent requiring certification.
What was the regulatory significance of the patent?
The patent did not create FDA marketing exclusivity. It created private patent rights enforceable under the Patent Act. FDA approval and patent protection operated through separate systems:
- FDA approval governed safety, efficacy, labeling, and manufacturing requirements.
- The Orange Book identified listed patents for approved drug products.
- The Hatch-Waxman framework governed patent certifications and potential generic stays.
- Patent expiration removed the patent-based obstacle but did not eliminate FDA requirements.
FDA approval of an oxycodone extended-release ANDA still required bioequivalence, abuse-control compliance, labeling conformity, and manufacturing controls. [2][4]
What Paragraph IV challenges affected the OxyContin patent estate?
Generic applicants challenged the original OxyContin patent estate through ANDA filings during the period when Purdue’s patents were listed. Purdue brought patent litigation against generic applicants seeking approval of oxycodone extended-release products.
The principal commercial effect of those disputes was delay or negotiated timing of generic entry. Once the relevant patents expired, the litigation value of claim 1 and claim 2 ended. Any historical 30-month stay associated with a Paragraph IV notice also expired with the underlying patent term.
Paragraph IV litigation involving OxyContin generally required analysis of:
- Whether the generic product met the claimed controlled-release profile.
- Whether the asserted claims were valid over prior art.
- Whether the generic label induced infringement of the method claims.
- Whether the listed patent properly covered the approved product.
- Whether the applicant’s formulation differed sufficiently from the patented technology.
Because the patent claims require administration to human patients, induced-infringement theories could be important for ANDA products. A generic applicant’s label, proposed dosing instructions, and expected use would be relevant to whether the product encouraged the claimed every-12-hour method.
Which companies challenged or competed with Purdue?
The competitive field included generic manufacturers and branded opioid companies that developed or marketed extended-release oxycodone products. Historical OxyContin patent disputes involved ANDA applicants, including major generic drug companies and specialty pharmaceutical manufacturers.
After patent expiration, competition expanded beyond a single patented product. Relevant competitive factors included:
- Generic oxycodone extended-release tablets.
- Abuse-deterrent oxycodone products.
- Alternative extended-release opioids.
- Transdermal opioid systems.
- Hydromorphone, morphine, and oxymorphone extended-release products.
- Non-opioid pain therapies.
The later market did not depend solely on the expired 5,508,042 patent. Abuse-deterrent technology, opioid prescribing controls, state restrictions, REMS obligations, and the broader opioid litigation environment became material commercial variables.
How strong was the patent estate for OxyContin?
The estate was strong during its enforceable term because it used overlapping protection types:
- Pharmacokinetic method claims.
- Controlled-release composition claims.
- Dosage-form and release-profile claims.
- Manufacturing and formulation know-how.
- Later abuse-deterrent formulation patents.
U.S. Patent 5,508,042 was commercially significant but technically narrow. Its vulnerability points included the need to prove the claimed pharmacokinetic parameters, the population-based “mean” limitations, the 12-hour steady-state condition, and the relationship between the approved label and the claimed treatment method.
The estate’s strength came from portfolio layering rather than from this patent alone. Once the original patents expired, later patents could protect redesigned products, particularly abuse-deterrent formulations, but those later rights did not revive the expired claims of U.S. 5,508,042.
What generic launch risks existed after expiration?
After expiration, patent risk from U.S. 5,508,042 was effectively removed. Remaining launch risks were primarily regulatory, commercial, and product-specific:
- FDA approval delays.
- Bioequivalence failure.
- Manufacturing deficiencies.
- Controlled-substance quota limits.
- DEA registration and supply-chain requirements.
- Product liability exposure.
- Abuse-deterrent labeling requirements.
- Market contraction caused by opioid prescribing restrictions.
- Competition from existing generic suppliers.
A generic manufacturer could launch without infringing the expired patent, but it still had to demonstrate that its product complied with FDA requirements and did not infringe separate unexpired patents covering a different formulation or abuse-deterrent architecture.
What geographic coverage did the patent provide?
U.S. Patent 5,508,042 provided rights only in the United States. It did not directly control oxycodone products in Canada, Europe, Japan, or other markets.
Foreign counterparts would require separate analysis by jurisdiction. Patent terms, claim scope, regulatory linkage, supplementary protection mechanisms, and litigation outcomes could differ materially. The expiration of the U.S. patent did not determine the status of foreign patents.
What manufacturing and intellectual-property barriers remain?
The expired patent does not prevent manufacture of a controlled-release oxycodone product. Manufacturing barriers may still include:
- Controlled-substance handling requirements.
- Specialized release-control manufacturing.
- Content uniformity and dissolution control.
- Stability testing.
- Scale-up validation.
- Abuse-deterrent formulation technology.
- Supply of pharmaceutical-grade oxycodone.
- FDA inspection and quality-system compliance.
Manufacturing know-how may remain commercially valuable even when patent rights have expired. Trade secrets, process controls, batch records, and supplier relationships can create practical barriers without creating patent exclusivity.
Key Takeaways
- U.S. Patent 5,508,042 covered a 12-hour controlled-release oxycodone treatment method with defined mean peak and trough plasma concentrations.
- Claim 1 focused on approximately 10 to 40 mg doses and tighter pharmacokinetic ranges.
- Claim 2 extended to approximately 160 mg but added the “substantially all human patients” limitation.
- The claims required repeated every-12-hour administration through steady state.
- The patent was a method-of-use and pharmacokinetic patent, not a blanket patent on oxycodone.
- Its U.S. exclusivity ended in 2013, subject to applicable term extensions.
- The patent is expired and does not create a current Orange Book barrier to generic entry.
- Residual risk would arise from separate formulation, abuse-deterrent, manufacturing, regulatory, or product-liability issues.
FAQs
Does U.S. Patent 5,508,042 cover immediate-release oxycodone?
No. The claims require an oral controlled-release formulation and a defined 12-hour pharmacokinetic profile.
Does the patent cover once-daily oxycodone?
No. The claims require repeated administration every 12 hours through steady-state conditions.
Can a generic manufacturer avoid the patent by using a different controlled-release technology?
During the patent term, potentially, if the product did not meet the claimed dose, pharmacokinetic, timing, or patient-population limitations. The patent is now expired, so it no longer creates an infringement barrier.
Is U.S. Patent 5,508,042 an abuse-deterrent patent?
No. The claims provided do not require physical, chemical, or tamper-resistant abuse-deterrent properties. They focus on controlled release and plasma concentration parameters.
Does expiration of this patent eliminate all OxyContin patent risk?
No. It eliminates risk from this patent only. Separate patents covering formulation, abuse deterrence, manufacturing, or later product versions require independent analysis.
References
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United States Patent and Trademark Office. (1996). U.S. Patent No. 5,508,042: Controlled release oxycodone compositions. U.S. Department of Commerce.
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U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations. FDA.
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U.S. Food and Drug Administration. (2001). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
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U.S. Food and Drug Administration. (2024). OxyContin prescribing information. Purdue Pharma L.P. and FDA.
