US Patent 11,060,128: Scope, Expiration, Orange Book Status, and 3,4-DAP Patent Landscape

US Patent 11,060,128 protects genotype-directed dosing of 3,4-diaminopyridine, also called amifampridine, for Lambert-Eaton myasthenic syndrome. The patent is directed to treatment methods for patients identified as N-acetyl transferase 2, or NAT2, slow acetylators. Its principal commercial relevance is to Firdapse, the Catalyst Pharmaceuticals product containing amifampridine phosphate.

The patent does not broadly claim 3,4-DAP, amifampridine phosphate, or every treatment of LEMS. Infringement generally requires proof of each claimed element, including the patient's LEMS diagnosis, NAT2 slow-acetylator status, and the specified daily dose or dosing regimen.

What does US Patent 11,060,128 cover?

US 11,060,128 covers methods of treating a human LEMS patient who is a NAT2 slow acetylator by administering specified daily amounts of 3,4-DAP or an equivalent amount of a pharmaceutically acceptable salt.

The independent claim structure is as follows:

Independent claim	Protected subject matter
Claim 1	LEMS treatment in a NAT2 slow acetylator using about 7.5 mg to about 40 mg of 3,4-DAP per day
Claim 21	LEMS treatment using about 7.5 mg to about 15 mg per day in divided doses
Claim 24	LEMS treatment using about 15 mg to about 30 mg per day in divided doses
Claim 27	LEMS treatment using 3,4-DAP phosphate equivalent to about 7.5 mg to about 30 mg of 3,4-DAP per day

The claims are method-of-treatment claims. They require administration to a patient and do not independently claim a tablet, suspension, active ingredient, salt, or manufacturing process.

What patient population is covered?

The required population is a human patient:

Diagnosed with LEMS;
In need of treatment;
Identified as a NAT2 slow acetylator.

Claim 20 further narrows claim 1 to a patient with renal impairment. This creates a potentially important overlap with renal-dose labeling, but renal impairment alone does not satisfy the NAT2 limitation.

The NAT2 limitation is central. A patient who receives the claimed dose but is not a NAT2 slow acetylator is outside the literal scope of the independent claims. A patient whose genotype or phenotype is unknown may create a proof issue in an infringement action, particularly where the prescribing information does not require NAT2 testing.

What dose ranges are protected by the patent?

The patent claims several overlapping dose ranges.

Dose category	Claims	Dosing details
Broad daily range	1	About 7.5 mg to about 40 mg
Lower range	17-19, 21-23	About 7.5 mg to about 15 mg
Intermediate range	12-16, 24-26	About 15 mg to about 30 mg
Phosphate-salt range	27-28	Phosphate equivalent to about 7.5 mg to about 30 mg
Divided doses	3, 13, 14, 18, 21, 23, 24, 26-28	Up to five doses, or specified two-to-four-dose regimens

The dependent claims identify 2.5 mg, 5 mg, 10 mg, 15 mg, and 20 mg divided-dose amounts. Claims 9 and 10 address scored tablets, including a scored 10 mg tablet. Claim 11 covers an aqueous suspension.

The word "about" expands the practical boundaries of the claimed ranges, but the scope is not unlimited. A dose materially above 40 mg per day, for example, would generally fall outside claim 1 unless another claim or patent covers it.

What formulations are protected by US 11,060,128?

The patent covers administration of:

3,4-DAP itself;
A pharmaceutically acceptable salt;
3,4-DAP phosphate;
Scored tablets or portions of scored tablets;
Aqueous suspensions.

The claims do not require a particular excipient, coating, tablet hardness, dissolution profile, particle size, or manufacturing process. The formulation limitations are therefore narrower than a conventional composition patent but broader than a claim limited to one commercial tablet design.

Claim 27 is commercially important because it expressly addresses 3,4-DAP phosphate by reference to the equivalent free-base dose. This language is directed to dose equivalence rather than a particular phosphate stoichiometry or tablet composition.

When does US Patent 11,060,128 expire?

The patent issued on August 17, 2021. Its effective expiration is expected in 2034 based on the patent family's March 2013 priority date and the standard United States patent-term framework. The operative date for commercial planning is the expiration date recorded in the USPTO and FDA Orange Book records, including any applicable patent-term adjustment.

Milestone	Date or status
Earliest disclosed priority period	March 2013
Patent issued	August 17, 2021
Expected base term endpoint	2034
Patent-term adjustment	Must be confirmed from the USPTO patent record
Patent-term extension	No extension is established from the supplied claim record
Pediatric exclusivity	No pediatric extension is established from the supplied claim record

Patent expiration and regulatory exclusivity are separate rights. Firdapse's orphan-drug exclusivity arose from FDA approval of amifampridine for LEMS and was scheduled to run for seven years from the approval date, subject to the statutory orphan-exclusivity rules. FDA approved Firdapse on November 28, 2018. The seven-year period therefore extended into November 2025, while the patent term continues beyond that period. [2]

What is the FDA and Orange Book status of Firdapse?

Firdapse is the relevant FDA reference product for this patent landscape. FDA approved Firdapse tablets containing amifampridine phosphate under NDA 208078 for adults with LEMS. The product is administered in divided doses, with dosing adjusted for tolerability and clinical response. [2]

Regulatory item	Firdapse status
Active ingredient	Amifampridine, supplied as amifampridine phosphate
Disease	Lambert-Eaton myasthenic syndrome
Dosage form	Oral tablets
FDA approval	November 28, 2018
NDA	208078
Reference product	Firdapse
Orphan exclusivity	Seven years from approval, subject to statutory conditions
Relevant patent	US 11,060,128
Orange Book relevance	Method-of-use patent listing and associated use-code analysis

A patent's Orange Book listing does not prove validity or infringement. It gives an ANDA applicant a basis to make a Paragraph IV certification and gives the patent holder a potential basis to file suit under the Hatch-Waxman framework. The precise listing, use code, and expiration date should be taken from the current Orange Book entry and FDA patent-listing record. [3]

How strong are the claims in US 11,060,128?

The estate is technically narrow but commercially relevant.

Strengths

The claims combine several limitations that can map onto a commercial prescribing regimen:

LEMS diagnosis;
3,4-DAP treatment;
Low-to-moderate daily doses;
Divided dosing;
Amifampridine phosphate;
Scored tablets;
Renal impairment in a dependent claim.

Claims 21, 24, and 27 create separate independent claim paths. A challenge that defeats one dose range may not eliminate every claim.

The claims also target pharmacogenetic variability. NAT2 acetylation status can affect the metabolism and exposure of 3,4-DAP. A patent directed to slow acetylators can capture a clinically meaningful subset of the treated population even though it does not cover all LEMS patients.

Weaknesses

The principal vulnerability is the NAT2 limitation. A generic applicant or prescriber may argue that:

the product label does not require NAT2 testing;
the provider does not know whether a particular patient is a slow acetylator;
the claimed population cannot be identified without genotyping or phenotyping;
the patent does not cover patients with other NAT2 phenotypes;
the claims require a treatment decision based on NAT2 status rather than an incidental biological fact.

The claims also depend on overlapping "about" ranges and dose-equivalence language. Those limitations may create enablement, written-description, indefiniteness, or claim-construction disputes, particularly if the specification does not provide sufficient clinical support across the full 7.5 mg-to-40 mg range and all listed dosage forms.

What Paragraph IV challenges could target this patent?

An ANDA applicant seeking approval of an amifampridine product could address US 11,060,128 through a Paragraph IV certification. Potential challenge theories include:

Invalidity based on anticipation or obviousness from earlier 3,4-DAP LEMS treatment regimens.
Lack of written description for NAT2-directed treatment across the full claimed dose range.
Lack of enablement for all claimed salts, formulations, dose schedules, and patient subgroups.
Indefiniteness involving "about," "equivalent amount," and NAT2 slow-acetylator status.
Noninfringement based on a label that omits NAT2 testing or does not direct treatment of NAT2 slow acetylators.
Noninfringement based on a dose, formulation, or dosing schedule outside the asserted claims.

A section viii "skinny label" strategy could be difficult if the FDA-approved indication and dosing instructions necessarily direct treatment of the claimed NAT2 population. It could be more viable if the generic label excludes pharmacogenetic dosing instructions and the patented use is separable from the unpatented LEMS use.

The patent holder could respond with an induced-infringement theory if the proposed label, prescribing information, or promotional materials direct administration to patients who meet the NAT2 and dosing limitations.

Which companies are relevant to the 3,4-DAP patent landscape?

Catalyst Pharmaceuticals

Catalyst commercializes Firdapse in the United States and is the principal commercial party associated with the Firdapse patent and regulatory estate. Its rights include product commercialization, FDA regulatory exclusivity, and patent claims directed to amifampridine treatment.

Jacobus Pharmaceutical

Jacobus developed and commercialized Ruzurgi, another amifampridine product for LEMS. Ruzurgi created the principal competitive and regulatory dispute involving amifampridine in the United States.

FDA and the Ruzurgi litigation

The FDA approved Ruzurgi in 2019 for pediatric patients with LEMS. Catalyst challenged the approval, arguing that Firdapse's orphan-drug exclusivity barred approval of the competing product for the same disease. The Eleventh Circuit ultimately vacated the FDA's approval decision in Catalyst Pharmaceuticals, Inc. v. Becerra, holding that FDA had not adequately accounted for the scope of Firdapse's orphan-drug exclusivity. [4]

That litigation was primarily an orphan-drug-exclusivity dispute, not a final adjudication that US 11,060,128 is valid and infringed. It nonetheless reduced the immediate competitive threat from Ruzurgi and strengthened the commercial importance of the Firdapse regulatory and patent package.

How does US 11,060,128 compare with core product and formulation patents?

Issue	US 11,060,128	Product or formulation patent
Claim type	Method of treatment	Composition, tablet, salt, or manufacturing process
Required patient	NAT2 slow acetylator with LEMS	Usually not required
Required dose	Yes	Usually no
Required administration	Yes	No, unless use claim
Covers phosphate salt	As an administered equivalent	May cover the salt itself
Generic risk	Label-driven and patient-specific	Product-driven
Proof burden	Requires treatment, dose, diagnosis, and patient phenotype	Requires product identity or process use
Design-around potential	Potentially significant	Often more limited for a required active ingredient

The patent is therefore strongest against a product label that expressly adopts NAT2-based dosing, low-dose divided administration, and amifampridine phosphate. It is weaker against a generic strategy that omits the patented pharmacogenetic use and relies on non-infringing labeling, provided the resulting label remains acceptable to FDA.

What generic launch scenarios exist?

Scenario 1: Paragraph IV challenge before patent expiration

A generic applicant challenges validity or noninfringement and accepts Hatch-Waxman litigation risk. A 30-month stay may delay approval if litigation is timely filed. The commercial outcome depends on claim construction, whether NAT2 status is required on the label, and whether FDA treats the patented use as separable.

Scenario 2: Launch after patent expiration

A generic launches after the effective patent term and any remaining regulatory exclusivity. This is the lowest legal-risk pathway but leaves the innovator with meaningful time to build market share before 2034.

Scenario 3: Skinny-label launch

The applicant excludes an expressly patented NAT2 dosing use. This strategy depends on whether the unpatented LEMS indication can be marketed without encouraging administration to NAT2 slow acetylators at the claimed doses.

Scenario 4: Alternative formulation

A generic uses a formulation outside claims 9-11, such as an unscored tablet or another liquid presentation. This does not avoid claims 1, 21, 24, or 27 if the product still administers the claimed dose of 3,4-DAP phosphate to the claimed patient population.

What is the revenue exposure?

Firdapse revenue is exposed to three separate events:

Expiration of orphan-drug exclusivity;
Approval of an ANDA or other competing product;
Loss, narrowing, or nonenforcement of the method-of-treatment patent.

Because US 11,060,128 is a use patent rather than a pure composition patent, a successful generic challenge could produce earlier competition than the patent's 2034 expiration if the generic avoids the claimed use. Conversely, if the Firdapse label incorporates the claimed dose and population, the patent could delay practical generic substitution even after orphan exclusivity ends.

Key Takeaways

US 11,060,128 is a pharmacogenetic method-of-treatment patent for LEMS.
The critical limitation is treatment of a NAT2 slow acetylator.
The broadest claimed dose is about 7.5 mg to about 40 mg of 3,4-DAP per day.
The commercial core includes amifampridine phosphate, divided dosing, scored tablets, and lower-dose regimens.
Claims 21, 24, and 27 provide separate independent claim positions.
Claim 20 specifically addresses renal impairment but does not remove the NAT2 requirement.
The patent issued August 17, 2021 and has an expected term extending into 2034, subject to the official USPTO term calculation.
Generic risk turns on Paragraph IV validity challenges, label design, and whether NAT2 slow-acetylator treatment can be carved out.
Ruzurgi was the principal competing amifamidine product, but the key appellate dispute concerned orphan-drug exclusivity rather than final validity of US 11,060,128.
The patent is commercially significant but narrower than a composition patent covering amifampridine phosphate itself.

FAQs About US Patent 11,060,128

Does US 11,060,128 cover every Firdapse prescription?

No. Literal coverage requires the claimed LEMS diagnosis, NAT2 slow-acetylator status, dose, and administration conditions. A prescription outside those elements may not infringe.

Does amifamidine phosphate itself infringe US 11,060,128?

Not by possession or manufacture alone. The asserted claims are method claims requiring administration to a qualifying LEMS patient.

Can a generic sell amifampridine before 2034?

Potentially, subject to FDA approval, regulatory exclusivity, patent certifications, litigation, and the generic label. A Paragraph IV challenge or a non-infringing label could support an earlier launch.

Is NAT2 testing required under the patent claims?

The claims require that the patient be a NAT2 slow acetylator. They do not expressly require a particular laboratory test, genotype assay, or phenotyping method.

Does a different tablet strength avoid the patent?

Not necessarily. Claims 1, 21, 24, and 27 are based primarily on total daily dose and patient population. A different tablet strength may avoid certain dependent claims, such as the scored 10 mg tablet claim, while still falling within broader claims.

References

United States Patent and Trademark Office. (2021). U.S. Patent No. 11,060,128: Methods of treating Lambert-Eaton myasthenic syndrome.
U.S. Food and Drug Administration. (2018). Firdapse prescribing information and approval history, NDA 208078.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book.
United States Court of Appeals for the Eleventh Circuit. (2023). Catalyst Pharmaceuticals, Inc. v. Becerra, concerning FDA approval of Ruzurgi and orphan-drug exclusivity.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Catalyst Pharms	FIRDAPSE	amifampridine phosphate	TABLET;ORAL	208078-001	Nov 28, 2018		RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial				METHOD OF TREATING LAMBERT-EATON MYASTHENIC SYNDROME WITH AMIFAMPRIDINE	⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Canada	2840591	⤷ Start Trial
World Intellectual Property Organization (WIPO)	2013003708	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 11,060,128

Which drugs does patent 11,060,128 protect, and when does it expire?

Summary for Patent: 11,060,128