United States Drug Patent 6,335,369: Claim Scope, Expiration, Orange Book Status, and Patent Landscape for L-Carnitine Dialysis Treatment

U.S. Patent No. 6,335,369 covers post-dialysis administration of L-carnitine, or an acceptable salt, to prevent or treat carnitine deficiency in chronic uremic patients. Its core inventive concept is timing the dose at the conclusion of dialysis rather than administering carnitine on a nonspecific schedule. The patent issued on January 1, 2002, and its enforceable term ended in 2019 under the modern 20-year patent-term framework, absent an unusual term adjustment or extension. The claims no longer create a current U.S. blocking right.

What does U.S. Patent 6,335,369 cover?

The patent covers a treatment method with four central limitations:

The patient has chronic uremia or end-stage renal disease.
The patient undergoes periodic dialysis.
L-carnitine or an acceptable salt is administered.
Administration occurs at the conclusion of dialysis.

The claims are directed to a method of medical treatment rather than to:

A new L-carnitine molecule;
A composition with a novel chemical structure;
A dialysis machine;
A manufacturing process;
A general nutritional use of carnitine; or
Every administration of levocarnitine to a renal patient.

The timing limitation is the principal point of differentiation. A claim requires administration "at the conclusion of dialysis." The patent therefore targets post-dialysis replacement therapy designed to compensate for carnitine removed during the dialysis session.

Patent identification

Field	Information
Patent	U.S. Patent No. 6,335,369
Title	Method of treating carnitine deficiency in patients undergoing dialysis
Patent type	Utility patent; method of treatment
Issue date	January 1, 2002
Technology	L-carnitine replacement in dialysis patients
Relevant active ingredient	L-carnitine, also called levocarnitine
Covered salts	Pharmaceutically acceptable salts; L-carnitine fumarate is expressly claimed
Core route	Intravenous administration after dialysis
Alternative route	Peritoneal administration
Core dose limitation	About 10 to about 20 mg/kg, calculated as L-carnitine
Commercial product association	Levocarnitine products, including Carnitor
U.S. term status	Expired in 2019

The patent’s claims, as supplied, contain fourteen claims. Claims 1, 6, and 10 are independent. The remaining claims depend from those three claim groups.

How are the 14 claims structured?

The claim set has three overlapping groups.

Claims 1 to 5: general post-dialysis treatment

Claim 1 is the broadest general treatment claim. It requires:

Prevention or treatment of carnitine deficiency;
A chronic uremic patient;
Periodic dialysis;
An effective amount of L-carnitine or a pharmaceutically acceptable salt; and
Administration at the conclusion of dialysis.

Claims 2 and 3 narrow the route to intravenous or peritoneal administration.

Claim 4 adds the most commercially specific regimen:

10 to 20 mg/kg;
Dose calculated as L-carnitine; and
Administration into a venous return line at the end of a dialysis session.

Claim 5 limits the active ingredient to L-carnitine fumarate.

Claims 6 to 9: L-carnitine fumarate subgroup

Claim 6 independently recites the same core method but requires L-carnitine fumarate rather than L-carnitine generally.

Claims 7 and 8 specify intravenous and peritoneal routes. Claim 9 adds the 10 to 20 mg/kg dose and venous-return-line administration.

Claim 6 is narrower in substance than claim 1 because it excludes other L-carnitine salts and requires fumarate. It is not merely a duplicate claim. It creates a separate enforcement route if the broader claim were invalidated.

Claims 10 to 14: long-term prevention regimen

Claim 10 is directed to preventing carnitine deficiency in end-stage uremic patients undergoing periodic dialysis over an extended period. It requires administration at the conclusion of each dialysis session.

This group adds two limitations not expressly required by claim 1:

The patient is an end-stage uremic patient; and
The treatment is repeated after each dialysis session over an extended period.

Claims 11 and 12 specify intravenous and peritoneal administration. Claim 13 adds the 10 to 20 mg/kg venous-return-line regimen. Claim 14 requires L-carnitine fumarate.

What is the broadest claim in U.S. Patent 6,335,369?

Claim 1 is the broadest general claim, but it is not broad in an absolute sense. It remains limited to a specific clinical population and treatment setting.

A practicing entity would need to satisfy all material elements:

Element	Required by claim 1?
Human patient	Implicit in medical-treatment context
Chronic uremia	Yes
Periodic dialysis	Yes
Carnitine deficiency prevention or treatment	Yes
L-carnitine or acceptable salt	Yes
Effective amount	Yes
Administration at conclusion of dialysis	Yes

A product manufacturer would not ordinarily infringe claim 1 merely by selling oral levocarnitine. Method-of-use infringement generally requires performance of the claimed method or conduct sufficiently connected to that performance. A label that instructs clinicians to administer levocarnitine after dialysis could create a stronger inducement theory while the patent is enforceable, but the patent term has ended.

What is the narrowest and most commercially specific claim?

Claims 4, 9, and 13 are the most operationally specific. They require approximately 10 to 20 mg/kg of carnitine, calculated as L-carnitine, delivered into a venous return line at the end of dialysis.

These claims map closely to a dialysis-center administration protocol. They are narrower than claims that merely require administration by the intravenous route because they specify:

A quantitative dose range;
The calculation basis for the dose;
The point of administration; and
The timing relative to the dialysis session.

A dose below 10 mg/kg or above 20 mg/kg would not literally satisfy the numerical limitation, although an expired patent cannot now be enforced. During the patent term, equivalents analysis could have been relevant, subject to prosecution-history and statutory limitations.

How does claim dependency affect the patent scope?

The dependent claims incorporate all limitations of the parent claim and add further restrictions. For example:

Claim 2 includes every limitation of claim 1 and adds intravenous administration.
Claim 4 includes claim 1 and adds dose and venous-line limitations.
Claim 5 includes claim 1 and requires L-carnitine fumarate.
Claim 9 includes claim 6 and adds the specific dose and venous-return-line regimen.
Claim 14 includes claim 10 and requires L-carnitine fumarate.

The claim groups therefore create layered protection. If a broad claim were found invalid for lack of novelty or obviousness, a narrower claim might survive if its particular route, dose, salt, or repeated-treatment limitation were patentably distinct. That protection is now historical because the patent has expired.

When did U.S. Patent 6,335,369 lose exclusivity?

The patent lost enforceable exclusivity in 2019. The applicable statutory framework generally provides a patent term of 20 years from the earliest effective U.S. nonprovisional filing date for applications filed after June 8, 1995. Patent term adjustment can modify the date, while patent term extension under 35 U.S.C. § 156 can apply to qualifying regulatory delays. [1]

The patent issued in 2002, but the issue date does not determine the end of the term. Based on the modern term calculation applicable to the patent, its enforceable life ended in 2019. No current generic entrant needs a license from the patent owner to practice the claimed post-dialysis levocarnitine regimen.

Exclusivity timeline

Event	Date or period
Patent application and priority chain	Earlier than the 2002 issue date
Patent issued	January 1, 2002
Core patent term	20 years from applicable U.S. filing basis
Enforceable term ended	2019
Current patent status	Expired
Current blocking effect	None from this patent

The patent cannot support a new Paragraph IV challenge because an expired patent does not create a live future-exclusivity dispute. A Paragraph IV certification may still be relevant to other unexpired Orange Book patents, but not to an expired patent standing alone.

What is the Orange Book status of U.S. Patent 6,335,369?

The Orange Book lists patents submitted by an NDA holder for an approved drug product. Patent listing is product-specific and does not automatically follow from a patent’s relevance to a drug.

U.S. Patent 6,335,369 is not a current blocking Orange Book patent for levocarnitine products. Any historical listing would not create present exclusivity after expiration. The FDA Orange Book must be reviewed by product and NDA to determine whether any other active patents remain listed for a specific levocarnitine dosage form. [2]

For Carnitor and generic levocarnitine products, the relevant regulatory questions include:

Whether the NDA holder listed the patent;
Whether the patent was listed against tablets, oral solution, or injection;
Whether a generic applicant submitted a Paragraph IV certification;
Whether any 30-month stay was triggered; and
Whether later patents covered a specific formulation or label.

The patent at issue is a method patent. Its potential Orange Book relevance would have depended on whether the patented method corresponded to an approved method-of-use indication and whether the NDA holder submitted it in the required form.

Does U.S. Patent 6,335,369 cover a formulation?

No. The claims do not require a particular dosage form, excipient system, concentration, container, pH, sterility specification, or manufacturing process.

L-carnitine fumarate is claimed as an active salt in claims 5, 6, and 14, but that limitation does not convert the patent into a formulation patent. A formulation patent typically claims a composition containing specified amounts of active ingredient and excipients. These claims instead recite administering the salt to a defined patient population after dialysis.

Potentially relevant distinctions include:

Technology	Covered by Patent 6,335,369?
IV levocarnitine administration after hemodialysis	Yes, subject to claim elements
Peritoneal administration after dialysis	Yes, expressly claimed
Oral levocarnitine composition	Not expressly claimed
Specific injectable excipients	No
Sterile manufacturing process	No
Dialysis apparatus	No
L-carnitine fumarate as a chemical product standing alone	No
Post-dialysis dose of 10-20 mg/kg	Yes, in claims 4, 9, and 13

What method-of-use protection does the patent provide?

The patent provides method-of-use protection for a defined dosing event. It does not claim all uses of levocarnitine in renal disease.

The strongest method-of-use features are:

Administration after the dialysis session;
Treatment or prevention of deficiency;
Chronic or end-stage uremia;
Periodic dialysis;
Repeated administration after each session for claims 10 to 14; and
A dose of 10 to 20 mg/kg for claims 4, 9, and 13.

A regimen administered before dialysis, during dialysis without post-session administration, or on a daily schedule unrelated to dialysis would not fall within the literal scope of the principal claims. A regimen for a patient with renal disease who does not undergo periodic dialysis also would not meet the claims.

How strong was the patent estate?

The patent estate was commercially focused but technically narrow. Its strongest attributes were clinical specificity and alignment with a practical dialysis protocol. Its weaknesses were the limited patient population, the requirement for post-dialysis timing, and the absence of composition or manufacturing claims.

Historical strength assessment

Factor	Assessment
Claim breadth	Moderate to narrow
Clinical specificity	High
Composition protection	None
Manufacturing protection	None
Dose protection	Narrow, but commercially relevant
Route coverage	IV and peritoneal
Salt coverage	Broad in independent claims; fumarate in dependent groups
Design-around potential	Significant
Current enforceability	None because expired

The claim set could have been designed around by changing the timing, dose, route, or clinical objective. A competitor using a different schedule might have avoided literal infringement, although the practical clinical value of the post-dialysis regimen could have made such a design-around less attractive.

Which companies challenged or competed against the patent?

No current patent challenge is required because the patent has expired. The competitive landscape is instead defined by generic levocarnitine suppliers and the availability of FDA-approved products.

Relevant commercial participants have included:

Sigma-Tau, associated with Carnitor;
Later holders or marketers of levocarnitine products;
Generic manufacturers of levocarnitine tablets, oral solution, and injection; and
Compounding and hospital suppliers operating under applicable FDA and state requirements.

The existence of a generic levocarnitine product does not establish that a particular manufacturer practiced every claim. Generic products may be sold with labels that omit a patented indication or may rely on labeling and certification strategies under the Hatch-Waxman framework.

What is the FDA regulatory status of levocarnitine?

Levocarnitine is an FDA-approved small-molecule drug. Carnitor has been approved in oral and intravenous forms for carnitine deficiency associated with defined metabolic or renal conditions. The FDA labeling for intravenous levocarnitine has included post-hemodialysis dosing in patients with end-stage renal disease. [3]

The approved label is important because it can overlap closely with claims 1, 4, and 10. Label overlap, however, does not revive an expired patent and does not establish that every generic label is legally identical to the historical patent disclosure.

Levocarnitine is not a biologic. Biosimilar regulation under the Public Health Service Act does not apply. Competition proceeds through the abbreviated new drug application pathway for qualifying generic products, not through biosimilar applications. [4]

Are there biosimilar risks for L-carnitine?

No. L-carnitine is a chemically defined small molecule, not a protein or other biological product. The relevant competitive risks are:

Generic substitution;
Abbreviated new drug applications;
Formulation differentiation;
Hospital purchasing contracts;
Injectable supply reliability; and
Label-based method-of-use strategies.

A biosimilar patent landscape analysis is therefore inapplicable to this product.

What generic entry risks exist for levocarnitine?

The principal generic-entry risks are regulatory and commercial rather than patent-based.

Generic entry scenarios

Scenario	Patent impact
Generic oral levocarnitine enters after patent expiration	No restriction from U.S. 6,335,369
Generic IV levocarnitine uses post-dialysis dosing	No restriction from expired patent
Generic uses L-carnitine fumarate	No restriction from expired patent
Generic label omits post-dialysis use	May reduce method-of-use exposure, but unnecessary for this expired patent
Competitor develops a new formulation	Must assess any separate live formulation patents
Hospital uses compounded levocarnitine	Patent 6,335,369 is not a current barrier

Commercial exposure is concentrated in the injectable and institutional segments, where dialysis-center protocols can support recurring demand. The patent itself no longer protects that revenue. Any current exclusivity would have to arise from separate patents, regulatory exclusivity, trademarks, supply contracts, or manufacturing capabilities.

What manufacturing and intellectual-property barriers remain?

U.S. Patent 6,335,369 does not create a manufacturing barrier. It does not claim:

Synthesis of L-carnitine;
Preparation of L-carnitine fumarate;
Sterile injectable production;
A specific impurity profile;
A crystal or polymorph;
A stable aqueous formulation; or
A dialysis-device delivery system.

Current barriers may instead include FDA approval, injectable manufacturing capacity, sterility validation, quality systems, controlled supply of pharmaceutical-grade material, and hospital purchasing access. Those are regulatory and operational barriers, not continuing rights under this patent.

What litigation or settlement agreements affected the patent?

The patent’s expiration removes the need for current infringement litigation based solely on U.S. Patent 6,335,369. Any historical litigation, settlement, or license agreement would have had value only during the enforceable patent term or as part of a broader commercial arrangement.

An expired patent can remain relevant to historical litigation analysis, invalidity records, prosecution-history estoppel, and damages periods. It cannot support prospective injunctive relief against current generic practice.

No current Paragraph IV settlement or active litigation involving this expired patent changes the present freedom-to-operate conclusion.

How does this patent compare with other levocarnitine patent categories?

Patent category	Example subject matter	Current relevance
Dialysis method patent	Post-dialysis administration, as in U.S. 6,335,369	Expired
Composition patent	Oral or injectable formulation with defined excipients	Must be checked separately
Salt or solid-form patent	L-carnitine fumarate form or crystalline material	Must be checked separately
Manufacturing patent	Chemical synthesis or purification	Must be checked separately
Label patent	Specific deficiency indication or patient subgroup	Must be checked separately
Device patent	Dialysis-line delivery system	Must be checked separately

The main diligence risk is assuming that expiration of this method patent clears every possible patent issue for a particular levocarnitine product. It clears this patent only. A product-specific freedom-to-operate review should separately evaluate active formulation, process, device, trademark, and regulatory rights.

Key Takeaways

U.S. Patent 6,335,369 claims post-dialysis administration of L-carnitine or an acceptable salt to chronic or end-stage uremic patients.
Claim 1 is the broadest general method claim.
Claims 4, 9, and 13 add the commercially specific 10 to 20 mg/kg dose and venous-return-line administration.
Claims 5, 6, and 14 specifically cover L-carnitine fumarate in the claimed treatment context.
Claims 10 to 14 require prevention, end-stage uremia, administration after each dialysis session, and extended treatment.
The patent is a method-of-use patent, not a formulation, manufacturing, or device patent.
The patent issued January 1, 2002, and its enforceable U.S. term ended in 2019.
It creates no current blocking right for generic levocarnitine or post-dialysis treatment.
Paragraph IV and biosimilar risks do not arise from this expired patent.
Current diligence should focus on separate active patents, FDA labeling, injectable manufacturing, and product-specific Orange Book records.

FAQs

Does U.S. Patent 6,335,369 cover oral levocarnitine?

Not expressly. The claims specify intravenous or peritoneal administration in dependent claims, while the independent claims require administration at the conclusion of dialysis. They do not claim a standalone oral formulation.

Does the patent cover every use of L-carnitine in dialysis patients?

No. The claims require a defined patient population, periodic dialysis, carnitine deficiency prevention or treatment, and administration at the conclusion of dialysis.

Does L-carnitine fumarate remain patented under this patent?

No. Claims 5, 6, and 14 cover L-carnitine fumarate only as part of the claimed post-dialysis treatment methods. The patent expired in 2019.

Can a generic company use the 10 to 20 mg/kg post-dialysis dose?

Yes, U.S. Patent 6,335,369 does not prevent that conduct today because the patent has expired. Other unexpired rights must be assessed separately.

Is Carnitor protected by an active patent estate based on U.S. Patent 6,335,369?

No. This patent no longer provides active U.S. patent protection. Any remaining commercial exclusivity would have to arise from other patents, regulatory rights, trademarks, contracts, or market conditions.

References

United States Code, 35 U.S.C. §§ 154, 156 (2023). Patent term and patent term extension provisions.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (2019). Carnitor (levocarnitine) injection and oral solution prescribing information.
United States Code, 42 U.S.C. § 262. Public Health Service Act provisions governing biological products and biosimilars.
United States Patent and Trademark Office. (2002). U.S. Patent No. 6,335,369: Method of treating carnitine deficiency in patients undergoing dialysis.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	3050201	⤷ Start Trial
Canada	2381187	⤷ Start Trial
European Patent Office	1257266	⤷ Start Trial
World Intellectual Property Organization (WIPO)	0152836	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,335,369

Summary for Patent: 6,335,369