United States Patent 6,025,391: Scope, Claims, Expiration, and Mycophenolate Patent Landscape

U.S. Patent No. 6,025,391 covers pharmaceutical compositions containing an enteric-coated pharmaceutically acceptable mycophenolate salt, particularly mycophenolate mofetil? No. The claims are directed to mycophenolate salts, with claim 5 identifying the mono-sodium salt. The patent therefore maps most directly to delayed-release mycophenolic acid sodium products such as Myfortic, not to CellCept, whose active ingredient is the chemically distinct prodrug mycophenolate mofetil.

The patent issued on February 15, 2000, from an application claiming priority to a 1996 filing. Its ordinary U.S. patent term expired in 2017, subject to any applicable patent-term adjustment or extension. It no longer creates a live exclusionary right in the United States. Its historical importance remains significant because it defined the core enteric-coated mycophenolate sodium product concept later commercialized by Novartis.

What does U.S. Patent 6,025,391 cover?

The patent covers two linked technical concepts:

A mycophenolate salt formulation designed to avoid release in the stomach and release the drug in the upper intestinal tract.
A composition or treatment method using an enteric-coated pharmaceutically acceptable mycophenolate salt, alone or with another immunosuppressant.

The patent is formulation-focused. It does not broadly claim every pharmaceutical use of mycophenolic acid, every mycophenolate product, or the mycophenolate mofetil prodrug.

Claim group	Subject matter	Scope
Claim 1	Composition adapted to prevent gastric release and release in the upper intestine	Functional delayed-release composition claim
Claim 2	Enteric-coated pharmaceutically acceptable mycophenolate salt	Core structural formulation claim
Claim 3	Immunosuppression method using the enteric-coated salt or claim 1 composition	Method-of-treatment claim
Claim 4	Composition containing the mycophenolate formulation and another immunosuppressant	Combination-composition claim
Claims 5-7	Mono-sodium mycophenolate	Narrower composition and method claims
Claim 8	Claim 3 method with cyclosporin	Narrower combination-treatment claim
Claims 9-11	Mono-sodium mycophenolate combined with cyclosporin	Narrower combination-composition claims

What is the claim construction of claim 1?

Claim 1 requires a pharmaceutical composition comprising a mycophenolate salt that is adapted to:

prevent release in the stomach; and
release the mycophenolate salt in the upper part of the intestinal tract.

The claim does not expressly require the words “enteric coating.” A formulation could potentially satisfy claim 1 through an enteric coating, a pH-dependent delivery matrix, or another technology that produces the required gastrointestinal release profile.

The practical infringement question is whether the accused product is designed to delay release until after gastric exposure and to release the active salt in the upper intestine. Product labeling, dissolution testing, coating composition, manufacturing specifications, and regulatory filings would be relevant to that analysis.

Claim 1 is broader in drafting form than claim 2 because it recites the release function rather than expressly requiring an enteric coating. Claim 2, however, is more conventional and easier to compare with a delayed-release tablet that visibly or technically contains an enteric film.

What does claim 2 protect?

Claim 2 covers a pharmaceutical composition comprising an enteric-coated pharmaceutically acceptable mycophenolate salt.

Its principal limitations are:

a pharmaceutical composition;
a mycophenolate salt;
pharmaceutical acceptability of the salt; and
an enteric coating.

The claim does not require:

a particular tablet size;
a specific coating polymer;
a defined dissolution threshold;
a particular dose;
mono-sodium mycophenolate; or
cyclosporin.

Those limitations appear in dependent claims or are absent from the claims entirely. A product with a different enteric polymer or different tablet excipients could therefore fall within the literal scope of claim 2 if it uses a pharmaceutically acceptable mycophenolate salt and provides an enteric coating.

The claim is directed to the finished composition, not merely to a coating material or manufacturing process.

How do claims 5 through 11 narrow the patent?

Claims 5 through 11 narrow the broad formulation and treatment claims in two ways.

First, they specify mono-sodium mycophenolate. This is the active ingredient associated with delayed-release mycophenolic acid sodium products. The mono-sodium limitation excludes other salts from the literal scope of those dependent claims.

Second, claims 8, 10 and 11 specify cyclosporin as the additional immunosuppressant. Those claims are narrower than claims referring generally to “another immunosuppressant.”

The dependent-claim structure is:

Dependent claim	Added limitation
Claim 5	Claim 1 composition with mono-sodium mycophenolate
Claim 6	Claim 2 composition with mono-sodium mycophenolate
Claim 7	Claim 3 method with mono-sodium mycophenolate
Claim 8	Claim 3 method with cyclosporin
Claim 9	Claim 4 composition with mono-sodium mycophenolate
Claim 10	Claim 9 composition with cyclosporin
Claim 11	Claim 4 composition with cyclosporin

A product can infringe an independent claim without meeting the narrower mono-sodium or cyclosporin limitations. Conversely, a product that satisfies the additional limitations may face multiple overlapping claim theories.

Does the patent cover Myfortic?

Yes, historically, the claims closely correspond to the Myfortic product concept.

Myfortic is a delayed-release tablet containing mycophenolic acid as the sodium salt, mycophenolate sodium. The product is designed to resist release in the stomach and release the active ingredient in the small intestine. The FDA label identifies Myfortic as an enteric-coated delayed-release tablet used for prophylaxis of organ rejection in patients receiving kidney transplants.[2]

The product-to-claim relationship is:

Myfortic characteristic	Relevance to U.S. 6,025,391
Mycophenolate sodium active ingredient	Supports claims 5-7 and 9
Delayed-release tablet	Supports claim 1
Enteric coating	Supports claim 2 and dependent claim 6
Immunosuppressive transplant indication	Supports claim 3
Potential use with cyclosporin	Relevant to claims 8, 10 and 11
Oral pharmaceutical composition	Satisfies the dosage-form context

The patent did not necessarily cover every commercial or regulatory feature of Myfortic. Separate patents could cover coating composition, dissolution performance, tablet architecture, excipients, manufacturing controls, or specific therapeutic uses.

Does U.S. 6,025,391 cover CellCept or mycophenolate mofetil?

The claims do not ordinarily read on CellCept merely because CellCept is converted into mycophenolic acid after administration.

CellCept contains mycophenolate mofetil, an ester prodrug. The claims of U.S. 6,025,391 require a mycophenolate salt. Mycophenolate mofetil is not the same chemical entity as mycophenolate sodium or another mycophenolate salt.

Product	Active ingredient	Direct fit with U.S. 6,025,391
Myfortic	Mycophenolate sodium	Strong historical fit
CellCept	Mycophenolate mofetil	Generally outside the literal salt limitation
Generic delayed-release mycophenolate sodium	Mycophenolate sodium	Strong historical fit
Immediate-release mycophenolate sodium	Mycophenolate sodium without enteric protection	Potentially outside claims 1 and 2
Enteric-coated alternative mycophenolate salt	Pharmaceutically acceptable mycophenolate salt	Potential claim exposure, depending on formulation

The distinction between a salt and an ester is central. A formulation containing mycophenolate mofetil would require a separate infringement analysis and would not be presumed to infringe this patent.

When did U.S. Patent 6,025,391 expire?

The patent issued in 2000 and was based on a 1996 priority date. Under the post-1995 U.S. patent-term framework, the ordinary term was approximately 20 years from the relevant nonprovisional filing date, producing an expiration in 2017. Public patent records identify the patent as expired.

Event	Date or period
Earliest priority period	1996
U.S. patent issuance	February 15, 2000
Patent term	Approximately 20 years from the relevant U.S. filing
Ordinary expiration	2017
Current status	Expired; no current exclusionary term

The exact expiration calculation can depend on the effective U.S. filing date, patent-term adjustment, terminal disclaimers, and any patent-term extension. The patent’s commercial blocking period nonetheless ended in 2017 under the publicly reported term information.[1]

Because the patent is expired, a current generic manufacturer would not need a Paragraph IV certification against this patent solely to address an unexpired patent right. Historical ANDA challenges could still have involved the patent while it was listed and unexpired.

What was the Orange Book status of U.S. 6,025,391?

U.S. Patent 6,025,391 was associated with the Myfortic regulatory and patent estate. Myfortic was approved by FDA in 2004 under NDA 021818.[2] The patent was part of the commercial exclusivity framework for the delayed-release mycophenolate sodium product.

The Orange Book distinguishes between:

patents claiming the drug substance;
patents claiming the drug product or formulation; and
patents claiming an approved method of use.

U.S. 6,025,391 is principally a drug-product and formulation patent. Its claims focus on the enteric-coated mycophenolate salt composition and related use. It is not a broad composition-of-matter patent for all mycophenolate activity.

The patent is no longer an active Orange Book barrier after expiration. Current generic approval analysis must focus on any later-listed patents, regulatory exclusivities, and the specific ANDA product.

What Paragraph IV risks applied to generic mycophenolate sodium?

Before expiration, a generic applicant seeking approval for delayed-release mycophenolate sodium could have used several technical and legal positions:

Invalidity: challenge anticipation, obviousness, enablement, written description, or indefiniteness.
Noninfringement: argue that the product does not use an enteric coating or does not prevent gastric release.
Salt distinction: use a different active form, although a different mycophenolate salt could still implicate the broader independent claims.
Release-profile distinction: design a formulation that releases outside the claimed upper intestinal region.
Expiration strategy: defer launch until the patent term ended.

The strongest noninfringement argument against claims 1 and 2 would generally involve an immediate-release product or a formulation that does not provide the claimed gastric protection. That strategy would not work for a generic intended to be therapeutically substitutable for Myfortic as a delayed-release product.

A Paragraph IV certification would have been relevant only while the patent was listed and unexpired. After expiration, the patent could no longer support a prospective injunction against a new generic launch.

What later patents could remain relevant after U.S. 6,025,391?

The expiration of U.S. 6,025,391 did not necessarily eliminate the entire Myfortic patent estate. Later patents may have addressed:

specific delayed-release compositions;
coating polymers;
dissolution specifications;
tablet formulations;
manufacturing processes;
stability improvements;
dosing regimens;
combination treatment;
organ-transplant immunosuppression methods.

A freedom-to-operate review should therefore separate the expired core patent from later patents associated with Myfortic or mycophenolate sodium. The relevant question is not whether a later patent cites U.S. 6,025,391, but whether it claims a feature required by the proposed generic product.

Patent category	Main risk after 2017
Enteric-coated mycophenolate salt broadly	Low from U.S. 6,025,391 because it expired
Specific coating formulation	Potentially relevant if later patent remains unexpired
Dissolution profile	Potentially relevant
Tablet excipient system	Potentially relevant
Manufacturing process	Relevant to production route, not necessarily finished product
Mycophenolate sodium indication	Potential method-of-use risk if patent remains listed and unexpired
Mycophenolate mofetil	Separate estate from the patent analyzed here

What manufacturing and formulation barriers did the patent create?

The commercial barrier was not limited to selecting mycophenolate sodium. A viable product had to deliver the active salt through the stomach while maintaining acceptable release, stability, content uniformity and bioavailability.

Relevant development issues included:

selection of an enteric polymer;
resistance to acidic gastric conditions;
rapid release at intestinal pH;
coating adhesion and mechanical durability;
protection of mycophenolate sodium from moisture;
tablet compression and coating compatibility;
dissolution reproducibility;
bioequivalence against the reference product;
scale-up of coating equipment and process controls.

These features could create practical barriers even after the patent expired. They do not independently extend the patent term, but they can increase development cost and delay generic approval.

How strong was the patent estate for Myfortic?

U.S. 6,025,391 was strong as a historical foundational patent for delayed-release mycophenolate sodium. Its strengths were:

direct alignment with the commercial product;
broad coverage of enteric-coated mycophenolate salts;
functional coverage through the gastric protection and intestinal release language;
dependent claims directed specifically to mono-sodium mycophenolate;
combination claims covering use with cyclosporin.

Its limitations were:

the absence of a broad claim to all mycophenolate products;
no direct coverage of mycophenolate mofetil;
dependence on proof of the claimed release behavior;
potential prior-art exposure concerning enteric-coated drug delivery;
expiration in 2017.

The patent was commercially important while active but has no present blocking power by itself.

What litigation and settlement issues affected this patent?

Patent disputes involving Myfortic or generic delayed-release mycophenolate sodium products would have centered on:

whether the generic product used an enteric-coated salt;
whether the release profile met the upper-intestinal limitation;
validity of the claims over earlier enteric-coated mycophenolate disclosures;
whether a later patent, rather than U.S. 6,025,391, controlled launch timing;
Paragraph IV notice and ANDA litigation;
potential launch dates under settlement agreements.

The expiration of U.S. 6,025,391 makes historical litigation against this patent less important for current launch decisions. A present-day review should examine any surviving related patents, FDA listing data, and the commercial terms of any generic settlements separately. The supplied claim set alone does not establish the existence or terms of a settlement agreement.

What is the current competitive landscape for mycophenolate products?

The market divides into two principal product families:

Product family	Active ingredient	Delivery profile	Patent relevance
CellCept and generic MMF	Mycophenolate mofetil	Immediate-release or capsule/tablet formulations	Separate prodrug patent estate
Myfortic and generic delayed-release products	Mycophenolate sodium	Enteric-coated delayed release	Directly related to U.S. 6,025,391

Myfortic competes primarily with generic mycophenolate sodium products. CellCept competes in a different chemical and formulation category, although both products are used for immunosuppression in transplant medicine.

Revenue exposure for the patent holder was concentrated in the delayed-release mycophenolate sodium franchise. Once the core patent expired, price competition and generic substitution became more important than patent enforcement. The commercial value of any surviving later patent depends on whether it covers the reference product’s essential formulation characteristics or only optional manufacturing features.

Key Takeaways

U.S. Patent 6,025,391 covers enteric-coated pharmaceutical compositions containing a pharmaceutically acceptable mycophenolate salt.
Claim 1 uses functional gastrointestinal-release language; claim 2 expressly requires an enteric coating.
Claims 5 through 7 and 9 narrow the scope to mono-sodium mycophenolate.
Claims 8, 10 and 11 add cyclosporin as the combination immunosuppressant.
The patent maps closely to Myfortic, whose active ingredient is delayed-release mycophenolate sodium.
The patent does not ordinarily cover CellCept’s mycophenolate mofetil by literal claim scope.
The patent issued in 2000 and expired in 2017 under its ordinary term.
It is no longer a current U.S. patent barrier to generic launch.
Later formulation, manufacturing, dissolution and method-of-use patents may still require separate review.
The principal current risk is the surviving patent estate and FDA product-specific requirements, not U.S. 6,025,391 itself.

FAQs About U.S. Patent 6,025,391

Is U.S. Patent 6,025,391 still enforceable?

No. Public patent records identify the patent as expired after its 2017 term. An expired patent cannot support a new U.S. patent infringement injunction.

Does a generic mycophenolate sodium tablet infringe claim 2?

Only if it contains a pharmaceutically acceptable mycophenolate salt with an enteric coating and otherwise satisfies the claim. Because the patent is expired, the issue is historical rather than a current infringement barrier.

Does the patent claim the use of mycophenolate for transplant rejection generally?

No. Claim 3 is a method claim requiring administration of an enteric-coated pharmaceutically acceptable mycophenolate salt or the claim 1 composition for immunosuppression. It is narrower than a claim to every use of mycophenolate in transplantation.

Are cyclosporin combination claims broader than the mono-sodium claims?

Yes. Claims 8 and 11 refer to cyclosporin without always requiring mono-sodium mycophenolate. Claims 10 requires both mono-sodium mycophenolate and cyclosporin, making it narrower.

Does patent expiration remove FDA bioequivalence requirements?

No. Patent expiration removes the patent-based exclusionary right. FDA approval still requires the applicable ANDA or other regulatory showing, including pharmaceutical quality, bioequivalence and labeling compliance.

References

United States Patent and Trademark Office. (2000). U.S. Patent No. 6,025,391, pharmaceutical compositions comprising mycophenolate salts.
U.S. Food and Drug Administration. (2004). Myfortic (mycophenolic acid) delayed-release tablets prescribing information. Novartis Pharmaceuticals Corporation.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
35 U.S.C. § 154. Patent term.
21 U.S.C. § 355. New drug applications and abbreviated applications.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9607564	Apr 12, 1996
United Kingdom	9622028	Oct 24, 1996

PCT Information
PCT Filed	April 10, 1997	PCT Application Number:	PCT/EP97/01800
PCT Publication Date:	October 23, 1997	PCT Publication Number:	WO97/38689

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0892640	⤷ Start Trial	91094	Luxembourg	⤷ Start Trial
European Patent Office	0892640	⤷ Start Trial	300157	Netherlands	⤷ Start Trial
European Patent Office	0892640	⤷ Start Trial	CA 2004 00024	Denmark	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,025,391

Summary for Patent: 6,025,391