United States Drug Patent 4,948,807: Claim Scope, Rivastigmine Coverage, Expiration and Patent Landscape

US Patent No. 4,948,807 covered three substituted phenyl carbamates, including rivastigmine, and methods of treating specified neurological disorders with those compounds. The patent issued on August 14, 1990, and its enforceable term expired in 2007 under the pre-URAA patent-term regime. It no longer blocks generic manufacture, sale, or use of rivastigmine in the United States.[1]

The commercially important compound in claim 3 is rivastigmine, also known as N-ethyl-N-methyl-3-[1-(dimethylamino)ethyl]phenyl carbamate. Rivastigmine was developed as Exelon by Novartis and is approved for Alzheimer’s disease and Parkinson’s disease dementia. The original patent did not claim a transdermal patch, a specific dosage form, a manufacturing process, or a particular formulation.

What compounds does US Patent 4,948,807 claim?

The patent claims three individual N-substituted phenyl carbamates and their pharmacologically acceptable salts.

Claim	Claimed compound	Commercial relevance
1	N-cyclohexyl-3-[1-(dimethylamino)ethyl]phenyl carbamate	One of the disclosed active compounds; not the principal U.S. commercial product
2	N-allyl-3-[1-(dimethylamino)ethyl]phenyl carbamate	One of the disclosed active compounds; not the principal U.S. commercial product
3	N-ethyl-N-methyl-3-[1-(dimethylamino)ethyl]phenyl carbamate	Rivastigmine
4	Treatment of listed neurological disorders with any of the three compounds or their acceptable salts	Method-of-use claim

The claims are species claims, not an open-ended genus covering every substituted phenyl carbamate. Each compound has the same 3-[1-(dimethylamino)ethyl]phenyl core and differs in the substituents attached to the carbamate nitrogen.

What is the chemical scope of claim 3?

Claim 3 covers rivastigmine in its free-base form and pharmacologically acceptable salts. Rivastigmine has the following commonly used identifiers:

Identifier	Information
Generic name	Rivastigmine
Chemical name	N-ethyl-N-methyl-3-[1-(dimethylamino)ethyl]phenyl carbamate
Drug class	Acetylcholinesterase inhibitor
Main U.S. brand	Exelon
Principal indications	Alzheimer’s disease dementia and Parkinson’s disease dementia
Common products	Capsules, oral solution and transdermal patches
FDA pathway for generics	Generally ANDA for therapeutically equivalent products

The claim does not expressly require a particular stereoisomer. Rivastigmine is commonly administered as the active enantiomer, but the precise stereochemical scope must be determined from the patent specification, prosecution history and applicable claim-construction law. The quoted claim language itself identifies the chemical structure without an explicit stereochemical limitation.

What does “pharmacologically acceptable salts thereof” cover?

The salt language extends claims 1 through 3 to pharmaceutically acceptable acid-addition salts of each named basic amine compound. It does not automatically cover:

New covalent derivatives;
Prodrugs;
Different carbamate N-substituents;
Formulations containing the compound;
Polymorphs unless they are legally treated as the claimed compound or salt;
Combination products as such; or
Unrelated analogues with changes to the phenyl substituent.

The salt limitation is dependent on the identity of the claimed parent compound. A salt of a different analogue would not fall within the literal salt language.

How should the method-of-treatment claim be interpreted?

Claim 4 covers administering a therapeutically effective amount of one of the three claimed compounds, or an acceptable salt, to a subject suffering from one of the listed disorders.

The listed conditions are:

Senile dementia;
Alzheimer’s disease;
Huntington’s chorea;
Tardive dyskinesia;
Hyperkinesia;
Mania;
Acute confusion disorders;
Friedrich’s ataxia; and
Down’s syndrome.

The claim requires both a qualifying condition and administration of a claimed compound. It does not specify:

Dose;
Dosing frequency;
Route of administration;
Duration;
Patient age;
Disease severity;
Formulation;
Treatment response; or
A particular biomarker.

That breadth would have made the claim commercially important during its term. The absence of a dosage or formulation limitation also means that the claim was not restricted to capsules, oral solution or patches.

Does claim 4 cover Parkinson’s disease dementia?

The quoted claim does not expressly list Parkinson’s disease dementia. A method treating Parkinson’s disease dementia would not automatically fall within claim 4 unless the condition could properly be characterized as one of the listed disorders or another claim or specification-based theory applied. The patent’s express recitation of Alzheimer’s disease is not equivalent to an unrestricted claim covering every dementia indication.

Does claim 4 cover off-label use?

During the patent term, the claim could potentially reach an unapproved use if the accused conduct involved administering a claimed compound to a patient suffering from one of the listed disorders. FDA approval status would not alone determine infringement. After expiration, the method claim has no continuing exclusionary effect.

When did US Patent 4,948,807 expire?

US 4,948,807 issued on August 14, 1990. Because it was subject to the pre-URAA patent-term rule, the ordinary term was 17 years from issuance. On that basis, the patent expired on August 14, 2007.[1]

Event	Date
Earliest reported priority	May 29, 1987
U.S. filing	1988
Patent issuance	August 14, 1990
Ordinary 17-year expiration	August 14, 2007
Current status	Expired

Patent-term adjustment under the modern 20-year system does not convert this patent into a currently enforceable patent. Any patent-term extension or other term calculation would have to appear in the official USPTO and FDA records. The patent is not a current barrier to U.S. generic rivastigmine entry.

What FDA exclusivity protected Exelon?

FDA regulatory exclusivity was separate from the patent term.

Exelon received FDA approval in 2000 for the treatment of mild to moderate dementia of the Alzheimer’s type. As a new chemical entity, the product received five years of NCE exclusivity under the Hatch-Waxman Act. That exclusivity would have ended in approximately April 2005, subject to the precise approval date and regulatory calculations.[2]

The 2007 expiration of US 4,948,807 occurred after the NCE exclusivity period. FDA exclusivity therefore did not preserve a continuing barrier after the patent expired.

Protection	Approximate end
Five-year NCE exclusivity for original Exelon approval	April 2005
US 4,948,807 patent term	August 2007
Current status	No active protection from US 4,948,807

What is the Orange Book status of US 4,948,807?

US 4,948,807 was associated with the original rivastigmine product and its active-ingredient protection. It is now expired and cannot support a current Paragraph IV enforcement action.

The Orange Book distinguishes among:

Active-ingredient patents;
Formulation patents;
Method-of-use patents; and
Other listed patents associated with an approved product.

An expired patent may remain visible historically in Orange Book records, but historical listing does not create an enforceable right. The relevant inquiry for a current generic applicant is whether an unexpired patent is listed against the reference product and whether the proposed product falls within that patent’s claims.[3]

Which patents protect rivastigmine formulations and patches?

The original patent is not a formulation patent. It does not claim:

A capsule;
An oral solution;
A transdermal patch;
A reservoir or matrix delivery system;
Adhesive composition;
Release-rate profile;
Patch size;
Specific excipients; or
A defined rivastigmine concentration.

Later rivastigmine patent activity focused on delivery systems, particularly transdermal administration. Those patents generally addressed the technical problems associated with delivering rivastigmine through the skin, controlling release and maintaining adhesion. They were separate from the compound claims in US 4,948,807.

Formulation and delivery patent categories

Patent category	Typical subject matter	Relation to US 4,948,807
Active ingredient	Rivastigmine molecule and salts	Directly covered by claims 1-3
Method of use	Treating specified neurological diseases	Directly covered by claim 4
Oral formulation	Capsules, oral solution, excipients and stability	Not claimed in US 4,948,807
Transdermal system	Patch, adhesive, matrix, release control	Not claimed in US 4,948,807
Manufacturing process	Synthesis, purification, crystallization	Not claimed in US 4,948,807
Solid-state form	Polymorphs, salts or crystalline forms	Not expressly claimed in the quoted claims

A generic capsule or oral solution applicant therefore faced a different patent analysis from a transdermal-patch applicant. Expiration of the compound patent removed the primary active-ingredient barrier but did not necessarily eliminate later formulation or delivery patents.

Are there biosimilar risks for rivastigmine?

No conventional biosimilar pathway applies. Rivastigmine is a chemically synthesized small-molecule drug, not a biologic subject to the Public Health Service Act biosimilar framework.

Competitive products generally enter through:

An ANDA under section 505(j), where the applicant demonstrates pharmaceutical equivalence and bioequivalence; or
A 505(b)(2) application where the product relies partly on FDA findings for the reference drug but differs in formulation, route, dosage form or other material respect.

The Purple Book is therefore not the relevant exclusivity source for rivastigmine. The Orange Book and FDA approval records are the principal regulatory sources.[3,4]

Did US 4,948,807 create Paragraph IV litigation risk?

During the patent term, an ANDA applicant seeking approval before expiration could have filed a Paragraph IV certification alleging that the patent was invalid, unenforceable or would not be infringed. Such a certification could trigger a patent-infringement action under the Hatch-Waxman framework.

After August 14, 2007, US 4,948,807 could not independently create a new 30-month stay based on its expiration. Any current litigation risk would arise from later unexpired patents, not from this patent.

Historic litigation significance

The patent presented several possible challenge theories during its life:

Anticipation: Whether the exact compounds or their salts were disclosed in an earlier reference.
Obviousness: Whether the claimed N-substituted carbamates would have been obvious from known aryl carbamates and cholinesterase inhibitors.
Written description and enablement: Whether the specification adequately supported all three compounds, their salts and the broad disease list.
Utility: Whether the neurological treatment uses were adequately supported by the disclosed pharmacological data.
Claim construction: Whether the structural language covered the relevant stereochemical form or only the expressly defined compound.

Because the claims are limited to three named compounds, an obviousness challenge would focus on the specific compounds and their demonstrated activity rather than on a broad genus.

How strong was the patent estate?

The original patent had high historical strength against products containing one of the three claimed compounds because claims 1 through 3 directly covered the active chemical entities. A product containing rivastigmine would have been exposed to claim 3 without requiring proof of a particular formulation or therapeutic use.

Its current strength is zero as an exclusionary right because the patent expired.

Dimension	Assessment
Compound coverage	Strong during term; direct coverage of rivastigmine
Salt coverage	Broad for pharmacologically acceptable salts of the named compounds
Formulation coverage	None apparent from the quoted claims
Manufacturing coverage	None apparent from the quoted claims
Method-of-use coverage	Broad disease list, but limited to three compounds
Current enforceability	None; patent expired
Biosimilar relevance	None
Generic relevance today	Historical only, except as prior art

The estate’s commercial value shifted over time from compound protection to lifecycle protection. Later patents, regulatory exclusivity, labeling strategy and transdermal delivery technology were more relevant to the launch and defense of generic products after the original compound patent expired.

What generic entry scenarios existed for rivastigmine?

Capsules and oral solution

Once the compound patent and NCE exclusivity expired, ANDA applicants could seek approval for therapeutically equivalent oral products. The principal patent issue was whether any later-listed formulation, process or method-of-use patent remained enforceable.

A generic applicant could use a Paragraph IV certification against an unexpired listed patent or a Paragraph III certification for a patent that had not yet expired. For an expired active-ingredient patent, the applicant would generally rely on the absence of an enforceable barrier.

Transdermal patches

Patch applicants faced a separate technical and patent analysis. Bioequivalence for a transdermal system can require more than simple oral pharmacokinetic comparison. Adhesion, delivery rate, residual drug, skin permeation and product design can affect approval and litigation exposure.

The patch market therefore had a later and more complex entry profile than the oral market, even though both products contained rivastigmine.

Which companies challenged or competed against Exelon?

The main competitive group consisted of generic pharmaceutical companies pursuing rivastigmine capsules, oral solution or patches through FDA abbreviated or hybrid approval pathways. Public records identify generic competition involving companies such as Dr. Reddy’s Laboratories, Teva, Mylan and other ANDA sponsors, depending on dosage form and approval period.[3,5]

The relevant distinction is between:

Companies challenging the expired compound patent;
Companies challenging later formulation or transdermal patents;
Companies receiving approval after patent expiration; and
Companies entering through non-infringing products or different regulatory pathways.

A current competitor analysis should therefore be product-specific. “Rivastigmine generic competition” is too broad to determine freedom to operate for a capsule, oral solution or patch.

What licensing deals affect the patent?

The patent was associated with the Sandoz research and corporate lineage that later became part of Novartis. The commercial brand Exelon was marketed by Novartis. The patent record alone does not establish the terms of any license, assignment, co-development agreement or settlement relating to the patent.

Corporate ownership and licensing must be separated:

Assignment: Transfers ownership of patent rights.
License: Authorizes use without necessarily transferring ownership.
Settlement: Resolves litigation and may impose launch or supply restrictions.
Corporate succession: Transfers rights through mergers, acquisitions or internal restructuring.

No current license can revive the expired exclusionary rights in US 4,948,807.

Key Takeaways

US 4,948,807 claims three substituted phenyl carbamates and their acceptable salts.
Claim 3 covers rivastigmine, the active ingredient in Exelon.
Claim 4 covers treatment of specifically listed neurological disorders with the three claimed compounds.
The patent does not claim a capsule, oral solution, transdermal patch, manufacturing process or specific dose.
The patent issued August 14, 1990, and its ordinary term expired August 14, 2007.
FDA five-year NCE exclusivity for original Exelon approval ended before the patent expired.
Rivastigmine is a small molecule, so biosimilar law does not apply.
Current generic risk depends on later formulation, transdermal and method-of-use patents, not US 4,948,807.
The patent has no current exclusionary value in the United States.

FAQs

Does US 4,948,807 cover the Exelon patch?

No. The quoted claims cover rivastigmine as a compound and methods of treatment. They do not recite a patch, adhesive, matrix, backing layer or transdermal release profile.

Can a company still file a Paragraph IV challenge to US 4,948,807?

Not in a commercially meaningful current sense. The patent expired in 2007. Any present Paragraph IV strategy would target a separate unexpired patent listed for the relevant rivastigmine product.

Does the patent cover rivastigmine hydrogen tartrate?

The claims cover pharmacologically acceptable salts of rivastigmine. Whether a specific salt falls within the claim depends on whether it is pharmacologically acceptable and whether the claimed salt language and specification support that interpretation.

Is rivastigmine protected by an Orange Book method-of-use patent today?

US 4,948,807 does not provide current protection. Any active method-of-use protection must be determined from the current Orange Book listings for the specific reference product and indication.

Can a manufacturer sell rivastigmine outside the United States based on this patent’s expiration?

The U.S. expiration does not determine rights in other countries. Patent term, supplementary protection, formulation patents and national claim scope must be assessed separately in each jurisdiction.

References

U.S. Patent No. 4,948,807. (1990). Substituted phenyl carbamates, their salts, a process for their preparation and their use. U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (2000). Exelon (rivastigmine tartrate) prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. FDA, Center for Biologics Evaluation and Research.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs database. FDA.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Israel	74497	Mar 05, 1985

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0193926	⤷ Start Trial	SPC/GB98/041	United Kingdom	⤷ Start Trial
European Patent Office	0193926	⤷ Start Trial	C980031	Netherlands	⤷ Start Trial
European Patent Office	0193926	⤷ Start Trial	98C0038	Belgium	⤷ Start Trial
Austria	58130	⤷ Start Trial
Australia	5428486	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,948,807

Summary for Patent: 4,948,807