United States Patent 5,206,248: Claim Scope, Expiration, and Dextromethorphan Patent Landscape

U.S. Patent 5,206,248 covers oral treatment of emotional lability and inappropriate emotional outbursts with centrally acting, non-addictive morphine analogs, particularly dextromethorphan and dextrorphan. Its claims also cover co-administration with an oxidative-degradation inhibitor, expressly including quinidine. The patent issued on April 27, 1993, and its original 17-year patent term expired on April 27, 2010, absent an unusual term adjustment or extension. It is no longer an enforceable barrier to generic entry.

The patent remains commercially important because its claims describe the pharmacological concept later used in NUEDEXTA, the dextromethorphan hydrobromide/quinidine sulfate product approved by the FDA for pseudobulbar affect. Current commercial protection depends on later patents, regulatory exclusivity, formulation rights, and Orange Book-listed patents, not on U.S. Patent 5,206,248.

What does U.S. Patent 5,206,248 protect?

The patent protects methods of reducing pathological or inappropriate emotional expression by orally administering a therapeutically effective amount of a non-addictive morphine analog that crosses the blood-brain barrier without materially impairing alertness or consciousness.

The core claim elements are:

Claim element	Scope
Patient	A human patient in need of treatment
Administration route	Oral administration
Active agent	A non-addictive analog of morphine
Distribution	The agent must penetrate the mammalian blood-brain barrier
Clinical effect	Reduction of emotional lability, spasmodic emotional outbursts, or inappropriate displays of emotion
Cognitive effect	No significant interference with consciousness or alertness
Preferred compounds	Dextromethorphan or dextrorphan
Mechanistic limitation in later claims	Interaction with dextromethorphan-binding receptors and suppression of excitatory neurotransmitter release
Combination limitation	Co-administration with a compound that inhibits oxidative degradation
Express combination	Quinidine

Claims 1 through 5 establish a general treatment method and then narrow it to dextrorotatory analgesic morphinans, dextromethorphan or dextrorphan, and quinidine-containing combinations.

Claims 6 through 10 add a pharmacological mechanism. Claims 11 through 15 use a broader symptom formulation focused on inappropriate emotional displays and emotional outbursts rather than the diagnostic term “emotional lability.”

How are the claims structured?

Claims 1 through 5: broad treatment and quinidine fallback

Claim 1 is the principal broad method claim. It does not expressly require dextromethorphan, dextrorphan, or quinidine. A compound could fall within the claim if it satisfies the functional requirements for a non-addictive morphine analog, central nervous system penetration, reduction of emotional outbursts, and preservation of alertness.

Claim 2 narrows claim 1 to a dextrorotatory enantiomer of an analgesic morphinan. Claim 3 narrows it further to dextromethorphan or dextrorphan.

Claims 4 and 5 address metabolic inhibition. Claim 4 covers co-administration with an oxidative-degradation inhibitor. Claim 5 identifies quinidine as the inhibitor.

The claims therefore create a hierarchy:

Functional class of centrally active non-addictive morphine analogs.
Dextrorotatory analgesic morphinans.
Dextromethorphan or dextrorphan.
Co-administration with an oxidative-degradation inhibitor.
Co-administration with quinidine.

Claims 6 through 10: mechanism-based treatment claims

Claim 6 requires the drug to react with dextromethorphan-binding receptors and suppress the release of excitatory neurotransmitters from neurons containing those receptors.

This limitation gives the claim a narrower technical profile than claim 1. A product may satisfy the clinical treatment requirement of claim 1 without satisfying every mechanistic limitation in claim 6. Conversely, a defendant could contest whether the accused compound reacts with the specified receptor population or whether it suppresses excitatory neurotransmitter release in the claimed manner.

Claims 7 through 10 repeat the same compound and quinidine limitations found in claims 2 through 5.

Claims 11 through 15: inappropriate emotional displays

Claim 11 targets patients suffering from inappropriate emotional outbursts. It requires oral administration, central nervous system penetration, interaction with dextromethorphan-binding receptors, suppression of excitatory neurotransmitter release, and reduction of outbursts without significant loss of alertness.

The phrase “inappropriate displays of emotion” potentially reaches conduct described clinically as pathological laughing, crying, or other involuntary affective expression. It is not limited on its face to amyotrophic lateral sclerosis or multiple sclerosis.

What compounds fall within the patent’s claimed scope?

Dextromethorphan is the central compound identified by the dependent claims. Dextrorphan is also expressly included, although its pharmaceutical use, tolerability, pharmacokinetics, and commercial status differ from dextromethorphan.

The compound scope can be divided into three categories:

Category	Examples	Claim position
Expressly named	Dextromethorphan, dextrorphan	Claims 3, 8, and 13
Narrow structural class	Dextrorotatory enantiomers of analgesic morphinans	Claims 2, 7, and 12
Functional genus	Non-addictive morphine analogs crossing the blood-brain barrier and reducing emotional outbursts	Claims 1, 6, and 11

The broad functional language creates potential claim-construction disputes. “Non-addictive,” “therapeutically effective quantity,” “significantly interfering,” “emotional lability,” and “inappropriate displays of emotion” are outcome- or characterization-based terms. Their interpretation would depend on the specification, prosecution history, expert evidence, and the factual record in a particular enforcement action.

The claims are method claims. They do not directly claim the compound dextromethorphan, quinidine, a tablet, a capsule, a salt, or a manufacturing process.

What formulations are protected by U.S. Patent 5,206,248?

The patent does not claim a specific dosage strength, tablet composition, capsule formulation, release profile, particle size, salt form, or fixed-dose ratio.

Its formulation-related scope is indirect. A product could potentially implicate the claims if it is orally administered and contains a claimed active agent, but the patent does not create a composition patent for a dextromethorphan/quinidine tablet.

The quinidine limitation is functional in claim 4 and compound-specific in claim 5. The claims do not require a particular dextromethorphan-to-quinidine ratio. This distinction matters because later product patents can claim specific dose combinations, dosage forms, or pharmacokinetic characteristics that are outside the express formulation scope of Patent 5,206,248.

NUEDEXTA contains dextromethorphan hydrobromide and quinidine sulfate. The FDA-approved strength is 20 mg dextromethorphan hydrobromide with 10 mg quinidine sulfate per capsule, administered initially once daily and, where appropriate, twice daily.[1]

When did U.S. Patent 5,206,248 expire?

The patent issued on April 27, 1993. For a pre-URAA U.S. patent, the ordinary term was 17 years from issuance. On that basis, the patent term ended on April 27, 2010.[2]

Event	Date
Patent issued	April 27, 1993
Ordinary statutory term	17 years from issuance
Expected expiration	April 27, 2010
Current enforceability	Expired
Current generic blocking effect	None from this patent

The patent was not the principal long-term exclusivity asset for NUEDEXTA because the FDA approved NUEDEXTA on October 29, 2010, after the patent’s expected expiration.[1] The commercial product therefore depended on later patent filings, regulatory exclusivity, and other intellectual-property rights.

What is the Orange Book status of Patent 5,206,248?

Patent 5,206,248 should not be treated as a current Orange Book barrier for NUEDEXTA. The patent expired before or around the time of NUEDEXTA’s initial FDA approval and does not provide an operative basis for a present-day 30-month stay against an ANDA applicant.

Orange Book-listed patents associated with an approved drug are evaluated based on the patents submitted by the NDA holder and accepted for listing by the FDA. The relevant commercial analysis for NUEDEXTA therefore requires review of later patents, including patents directed to dextromethorphan/quinidine treatment methods and related product protection, rather than reliance on Patent 5,206,248.[3]

What later patents protect NUEDEXTA?

Later patent protection was directed more specifically to the dextromethorphan/quinidine combination, treatment of pseudobulbar affect, and related dosing or formulation concepts.

Public FDA labeling has identified later U.S. patents associated with NUEDEXTA, including U.S. Patent Nos. 7,659,282 and 8,338,437.[1] Those patents are commercially more relevant than U.S. Patent 5,206,248 because they were filed and prosecuted under the post-URAA patent-term regime and were connected to the approved product’s later development.

Patent	General relevance	Commercial significance
5,206,248	Emotional lability treatment with dextromethorphan-type agents	Expired foundational method patent
7,659,282	Later dextromethorphan/quinidine treatment or composition protection	Potential Orange Book relevance
8,338,437	Later NUEDEXTA-related treatment protection	Potential Orange Book relevance
Later continuations or related patents	Dosing, formulation, or method refinements	Must be assessed by current Orange Book and USPTO status

Patent numbers alone do not establish current enforceability. Expiration, terminal disclaimers, maintenance fees, patent-term adjustment, reissue history, and Orange Book listing status must be checked for each later patent.

How strong is the patent estate for the claimed therapy?

Patent 5,206,248 has no current blocking strength because it is expired. Its historical strength was stronger at the concept level than at the formulation level.

Strengths of the original patent

It claimed the therapeutic use of dextromethorphan and dextrorphan for emotional lability.
It covered both symptom-based and mechanism-based treatment theories.
It expressly included quinidine as a metabolic inhibitor.
It used functional language that could reach compounds beyond the named examples.
It was directed to a clinically differentiated use of a known compound.

Weaknesses of the original patent

It does not claim a specific commercial formulation.
It does not claim a fixed dose or dose ratio.
It does not claim a particular salt, tablet, capsule, or release technology.
Its functional terms could create enablement, written-description, definiteness, or claim-construction disputes.
The patent is expired and cannot support current infringement litigation.

The strongest surviving protection is likely to arise from later patents that tie the invention to a defined product, regimen, indication, or formulation.

What Paragraph IV challenges and generic entry risks exist?

An ANDA applicant seeking approval for a generic dextromethorphan/quinidine product must address any unexpired patents listed for the reference product. Under the Hatch-Waxman framework, a Paragraph IV certification alleges that a listed patent is invalid, unenforceable, or will not be infringed.[4]

Patent 5,206,248 itself creates no current Paragraph IV risk because it has expired. The relevant risks are:

A Paragraph IV challenge to an unexpired method patent.
Litigation filed within 45 days of receiving the certification.
A potential 30-month approval stay under the Hatch-Waxman statute.
A launch date controlled by patent expiration, litigation outcome, settlement, or pediatric exclusivity.
A carve-out strategy excluding patented indications from the generic label.

Because the patent claims treatment of emotional lability and inappropriate emotional outbursts, a generic applicant may face a label-scope problem if a later patent covers the approved pseudobulbar-affect indication. A section viii “skinny label” strategy may be difficult where the patented use is central to the reference product’s labeling, although the feasibility depends on the exact Orange Book claims and FDA labeling.

Which companies are challenging the NUEDEXTA patent estate?

The relevant competitive field includes generic-drug manufacturers capable of filing ANDAs for dextromethorphan hydrobromide/quinidine sulfate and companies seeking to commercialize alternative treatments for pseudobulbar affect.

A definitive list of current challengers requires the live FDA Orange Book, Paragraph IV notices, federal court dockets, and settlement records. Patent 5,206,248 does not itself identify a current challenger because it is expired and no longer supports an active enforcement campaign.

No biosimilar pathway applies. NUEDEXTA is a small-molecule drug, so competitive entry proceeds through the ANDA pathway rather than the biosimilar provisions of the Public Health Service Act.

What is the FDA regulatory status of the claimed therapy?

The FDA approved NUEDEXTA on October 29, 2010, under NDA 021879 for the treatment of pseudobulbar affect.[1] Pseudobulbar affect is characterized by involuntary and inappropriate episodes of laughing or crying and is associated with neurological conditions including ALS and multiple sclerosis.

The approved product combines:

Dextromethorphan hydrobromide, the centrally acting component.
Quinidine sulfate, which inhibits CYP2D6-mediated metabolism and increases dextromethorphan exposure.

The approved indication overlaps materially with the emotional-lability and inappropriate-emotional-display concepts described in Patent 5,206,248. The regulatory approval, however, does not revive the expired patent or expand its legal term.

How does Patent 5,206,248 compare with later NUEDEXTA patents?

Issue	U.S. Patent 5,206,248	Later NUEDEXTA patents
Primary focus	Broad therapeutic concept	Commercial product and approved-use protection
Named active agents	Dextromethorphan and dextrorphan	Primarily dextromethorphan with quinidine
Quinidine	Expressly claimed as a metabolic inhibitor	Often integrated into product or regimen claims
Dosage specificity	None apparent from supplied claims	More likely to include dosing or product limitations
Formulation protection	No direct composition claim	May include product or dosage-form limitations
Patent term	Expired in 2010	Later terms potentially extend into the 2020s
Current litigation value	None	Depends on live patent and Orange Book status
Generic-entry effect	No present effect	Potential ANDA and Paragraph IV relevance

Key Takeaways

U.S. Patent 5,206,248 is a foundational method patent for treating emotional lability with centrally acting non-addictive morphine analogs.
Dextromethorphan, dextrorphan, and quinidine are expressly addressed by dependent claims.
The claims are method claims, not direct claims to a tablet, capsule, dosage strength, or fixed-dose composition.
The patent’s ordinary term expired on April 27, 2010.
It cannot create a current Orange Book or Paragraph IV barrier.
NUEDEXTA was FDA-approved on October 29, 2010, for pseudobulbar affect.
Current generic-entry risk depends on later patents, Orange Book listings, litigation, settlements, and regulatory exclusivity.
No biosimilar pathway applies because NUEDEXTA is a small-molecule drug.
The commercial value of the original patent is historical and foundational; surviving protection must be assessed patent by patent.

FAQs About U.S. Patent 5,206,248 and NUEDEXTA

Is U.S. Patent 5,206,248 still enforceable?

No. Based on its April 27, 1993 issuance date and the pre-URAA 17-year patent term, it expired on April 27, 2010.

Does Patent 5,206,248 claim NUEDEXTA?

It covers the therapeutic concept embodied by NUEDEXTA, including oral dextromethorphan treatment and co-administration with quinidine. It does not appear from the supplied claims to claim the specific NUEDEXTA capsule formulation or commercial dose.

Can a generic manufacturer challenge Patent 5,206,248 under Paragraph IV?

No current Paragraph IV challenge is necessary against this patent because it has expired. A generic applicant would address any later unexpired Orange Book-listed patents.

Does the patent cover pseudobulbar affect in ALS and multiple sclerosis?

The claims do not expressly limit treatment to ALS or multiple sclerosis. Their language covers emotional lability, inappropriate emotional displays, and emotional outbursts in human patients. The FDA-approved NUEDEXTA indication is pseudobulbar affect, including patients with ALS or multiple sclerosis.

Is quinidine required by the independent claims?

No. Claims 1, 6, and 11 do not require quinidine. Quinidine appears in dependent claims 5, 10, and 15 as the compound that inhibits oxidative degradation of the active morphine analog.

References

U.S. Food and Drug Administration. (2010). NUEDEXTA (dextromethorphan hydrobromide and quinidine sulfate) prescribing information.
United States Patent and Trademark Office. (1993). U.S. Patent No. 5,206,248: Treatment of emotional lability with dextromethorphan.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book.
U.S. Food and Drug Administration. (2017). Guidance for industry: 180-day exclusivity when multiple first applicants are eligible for 180-day exclusivity.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Canada	2114267	⤷ Start Trial
Canada	2712821	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,206,248

Summary for Patent: 5,206,248