United States Patent 11,274,332: Scope, Claim Analysis, and Patent Landscape for Amifampridine in LEMS

United States Patent 11,274,332 protects genotype-directed dosing of 3,4-diaminopyridine, also known as amifampridine, for patients with Lambert-Eaton myasthenic syndrome who have two NAT2 slow alleles. Its principal commercial significance is the overlap between the claimed dosing regimens and FDA-approved Firdapse treatment, particularly for NAT2 poor metabolizers and patients with renal impairment.

The patent is a method-of-treatment patent. It does not claim 3,4-diaminopyridine as a chemical compound, the general treatment of LEMS, or every formulation of amifampridine. Infringement requires practice of the specified genotype-linked dosing method.

What does United States Patent 11,274,332 claim?

The patent has four independent claims: claims 1, 18, 21, and 24. The claims divide the invention into a broad dosing range, two narrower dose bands, and a phosphate-salt-specific embodiment.

Independent claim	Patient requirement	Active ingredient	Dose	Administration
Claim 1	LEMS; two NAT2 slow alleles	3,4-DAP or pharmaceutically acceptable salt	About 7.5-40 mg/day	Divided doses optional
Claim 18	LEMS; two NAT2 slow alleles	3,4-DAP or salt	About 7.5-15 mg/day	Divided doses required
Claim 21	LEMS; two NAT2 slow alleles	3,4-DAP or salt	About 15-30 mg/day	Divided doses required
Claim 24	LEMS; two NAT2 slow alleles	3,4-DAP phosphate salt	Equivalent to about 7.5-30 mg/day of 3,4-DAP	Divided doses required

The claims therefore establish three overlapping dose categories:

A broad 7.5-40 mg daily range.
A lower 7.5-15 mg daily range.
A middle 15-30 mg daily range.
A phosphate-salt range equivalent to 7.5-30 mg of free-base 3,4-DAP.

The claim set is structured so that a product or treatment regimen falling within a narrower dependent claim will usually also fall within claim 1, assuming the remaining limitations are met.

What patient population is protected by the patent?

The required population is a human patient diagnosed with LEMS who has two NAT2 slow alleles.

This is a substantially narrower population than all LEMS patients. The patent does not cover treatment of:

Patients with two NAT2 rapid alleles.
Patients with two NAT2 intermediate alleles unless they also meet the claimed slow-allele limitation.
Patients whose NAT2 status is unknown.
Nonhuman subjects.
Patients treated for another neuromuscular disorder.
Patients receiving 3,4-DAP without a LEMS diagnosis.

The claims do not expressly require that the clinician perform a NAT2 genetic test before treatment. They require that the patient have the genotype. A product label, prescribing protocol, genetic test, clinical record, or other evidence could be relevant in assessing whether a treatment falls within the claims.

Which NAT2 mutations are covered?

Claims 2, 19, and 22 identify the following mutations:

282T
341C
191A
481T
590A
857A

Claims 3, 20, and 23 narrow the population to alleles containing:

282T;
341C; or
both 282T and 341C.

Claim 2 uses "one or more of" the listed mutations. The claim language indicates that each of the two NAT2 slow alleles must contain at least one listed mutation. The narrower claims focus on the 282T and 341C variants.

The mutation shorthand in the claims should be compared against the nomenclature used in the relevant genetic-testing platform and FDA labeling. Variant notation can differ depending on whether numbering refers to genomic DNA, coding DNA, or protein sequence.

How broad is the dose protection?

Claim 1 is the broadest dosing claim. It covers a total daily dose of about 7.5 mg to about 40 mg of 3,4-DAP or its salt equivalent.

The term "about" creates a potential claim-construction issue. Courts generally assess the term in light of the specification, prosecution history, technical context, and whether a skilled person would understand the permitted variation. The claim should not automatically be read as covering every dose near the endpoints.

The core dose bands are:

Claimed dose	Related claims	Commercial relevance
About 7.5 mg/day	1, 14, 16, 18, 24	Low-dose treatment
About 15 mg/day	1, 9, 12, 18, 21, 24	Starting or reduced regimen
About 30 mg/day	1, 9, 13, 21, 24	Standard middle-range regimen
More than 30 to about 40 mg/day	Claim 1	Broadest dose-only coverage

The patent does not claim the FDA-approved maximum dose as such. The significance of the 40 mg upper boundary is that it extends beyond the narrower 7.5-30 mg and 7.5-15 mg independent claims.

What formulations and dosage forms are protected?

The patent covers 3,4-DAP itself and pharmaceutically acceptable salts. Claim 4 expressly identifies 3,4-DAP phosphate salt.

Claims 6-8 add dosage-form limitations:

One or more scored tablets or portions of scored tablets.
Tablets containing about 10 mg of 3,4-DAP or its salt equivalent.
An aqueous suspension.

These claims do not appear to require a particular excipient, coating, release profile, particle size, manufacturing process, or tablet shape based on the claim text supplied.

The scored-tablet claims are commercially relevant because dividing a 10 mg tablet can implement the low daily doses covered by the patent. The aqueous-suspension claim creates separate coverage for liquid dosing, which may be relevant to patients unable to swallow tablets or to dose adjustments below a full tablet.

Does the patent cover Firdapse?

Firdapse contains amifampridine, the pharmaceutical product form of 3,4-DAP. FDA labeling identifies Firdapse as an oral product for adults with LEMS and provides divided-dose administration. The label also includes dosing considerations for patients who are NAT2 poor metabolizers and for patients with renal or hepatic impairment.[1]

Whether a particular Firdapse prescription infringes depends on all claim limitations. A treatment may fall within the patent if:

The patient has LEMS.
The patient has two NAT2 slow alleles.
The prescribed total daily amount falls within the claimed range.
The product is 3,4-DAP or a covered salt.
Any applicable divided-dose, tablet, suspension, or phosphate-salt limitation is satisfied.

The patent does not automatically cover every sale of Firdapse because the claims are patient-specific and regimen-specific.

What is the significance of the renal-impairment claim?

Claim 17 depends on claim 1 and adds renal impairment. It covers treatment of a patient who has both:

Two NAT2 slow alleles; and
Renal impairment.

This is a narrow intersection of pharmacogenomic and clinical-risk factors. Renal impairment alone is insufficient. A patient with renal impairment but without two NAT2 slow alleles would not satisfy claim 17, although another claim could still be relevant if the patient meets its genotype and dose limitations.

The claim may be important in product labeling and clinical decision support because both NAT2 metabolism and renal clearance can affect systemic exposure. A label-directed dose reduction for a genetically defined patient with renal impairment could create a stronger factual basis for method-of-use enforcement.

How do the claims compare with FDA-approved dosing?

FDA-approved Firdapse labeling provides divided oral dosing for LEMS and identifies lower dosing considerations for NAT2 poor metabolizers. The patent claims overlap with the lower ranges used for genotype-linked dosing but are not identical to the entire label.

Issue	Patent claims	FDA labeling relevance
Indication	LEMS	Firdapse is approved for adult LEMS
Genotype	Two NAT2 slow alleles	Label discusses NAT2 poor metabolizer status
Dose	About 7.5-40 mg/day in claim 1	Label contains standard and reduced dosing
Divided dosing	Required in claims 18, 21, and 24	Label uses divided administration
Phosphate salt	Expressly covered in claim 24	Product salt form is relevant
Renal impairment	Claim 17	Label contains renal-impairment dosing information
Tablet	Scored tablet and about 10 mg embodiment	Relevant to practical dose splitting
Suspension	Expressly covered in claim 8	Applies only if an aqueous suspension is used

The regulatory label can be relevant to induced-infringement analysis, especially if a patented use is included in the approved indication or prescribing information. FDA approval itself does not determine patent infringement.

When does United States Patent 11,274,332 lose exclusivity?

The patent issued on March 15, 2022. Its enforceable term depends on the earliest effective nonprovisional filing date, any priority claims, patent-term adjustment, patent-term extension, and terminal disclaimers recorded in the USPTO file history.[2]

A reliable expiration date cannot be calculated from the claims alone. The relevant term is generally 20 years from the earliest effective U.S. nonprovisional filing date, subject to statutory adjustments under 35 U.S.C. §§ 154 and 156.[3]

The patent should be reviewed in USPTO Patent Center for:

The earliest priority application.
Patent-term adjustment.
Terminal-disclaimer statements.
Continuation or divisional relationships.
Assignment history.
Post-grant certificates.
Certificates of correction.
Maintenance-fee status.

A patent expiration estimate based only on the grant date would be unreliable.

What is the Orange Book status of the patent?

The FDA Orange Book generally lists patents submitted by the holder of an approved new drug application that claim the drug substance, drug product, or an approved method of use.[4]

A method-of-treatment patent may be Orange Book-listed if it claims an approved use and satisfies FDA listing requirements. The presence or absence of a listing should be verified against the current Orange Book entry for Firdapse and the patent-use codes associated with that product.

The supplied claim text alone does not establish whether Patent 11,274,332 is currently listed in the Orange Book, whether it has a patent-use code, or whether FDA accepted the listing. Those are regulatory-record questions distinct from claim scope.

Are Paragraph IV challenges likely to apply?

A Paragraph IV certification is relevant when an ANDA applicant seeks approval before expiration of an Orange Book-listed patent and asserts that the patent is invalid, unenforceable, or not infringed.[5]

For this patent, the practical Paragraph IV analysis would focus on whether an ANDA product and proposed labeling would direct treatment of:

LEMS patients;
Patients with two NAT2 slow alleles;
Patients receiving 7.5-40 mg/day;
Patients receiving divided doses;
Patients receiving the claimed phosphate salt.

A generic applicant could attempt a "section viii" carve-out if the patented genotype-specific use is omitted from labeling and the remaining label does not encourage the patented method. That strategy becomes more difficult if the approved label itself includes NAT2-guided dosing or if ordinary prescribing instructions encourage the claimed regimen.

Potential invalidity issues include:

Anticipation by prior clinical or pharmacogenomic disclosures.
Obviousness based on known 3,4-DAP dosing, NAT2 metabolism, and LEMS treatment.
Written-description support for the full 7.5-40 mg range.
Enablement of all listed NAT2 variants.
Definiteness of "about," "slow alleles," and "equivalent amount."
Obviousness-type double patenting over related dosing patents.

Which companies are most exposed?

Catalyst Pharmaceuticals is the principal commercial company associated with Firdapse in the United States. Its exposure is tied to the extent to which the patent protects an approved or commercially used regimen.

Potentially exposed parties include:

ANDA applicants seeking amifampridine approval.
Compounding pharmacies preparing 3,4-DAP suspensions.
Specialty pharmacies dispensing divided or split doses.
Digital prescribing platforms that recommend genotype-specific dosing.
Laboratories or service providers that direct treatment based on NAT2 results.
Competitors developing an alternative amifampridine salt or formulation.

A competitor can reduce risk by avoiding the claimed population, omitting the patented use from labeling where legally available, using a noncovered dose, or challenging validity and enforceability. These strategies must be evaluated against induced-infringement principles and the actual proposed label.

How strong is the patent estate?

Patent strength is mixed.

Strengths

The claims identify a clinically defined population.
The genotype limitation narrows the field in a way that may be difficult to design around while retaining genotype-directed dosing.
The claims cover both free-base-equivalent dosing and phosphate salt use.
The claim set includes tablets, divided tablets, and aqueous suspensions.
Renal impairment creates an additional high-risk subgroup.
The claims overlap with regulatory dosing concepts for NAT2 poor metabolizers.

Vulnerabilities

The claims are method claims rather than compound claims.
Infringement depends on patient genotype and actual dosing.
A generic label may attempt to omit or carve out the patented use.
"About" and "equivalent amount" may require construction.
Prior-art pharmacogenomic dosing disclosures could challenge obviousness.
The mutation definitions should be tested against the specification and prosecution history.
The patent does not, based on the supplied claims, cover every amifampridine product or every LEMS treatment.

What patent litigation and settlements affect this patent?

The claim text does not establish current litigation, Paragraph IV notices, settlements, licenses, or covenant-not-to-sue agreements involving Patent 11,274,332. Those matters must be determined from PACER, district-court dockets, FDA records, USPTO assignment records, and the Orange Book.

A litigation review should search for:

ANDA cases under the Hatch-Waxman Act.
Declaratory-judgment actions.
Patent-license agreements involving Catalyst Pharmaceuticals or Firdapse.
Settlements containing launch dates or permitted-label restrictions.
Inter partes review petitions.
Post-grant review or reexamination proceedings.
Antitrust or improper-listing challenges.

Key Takeaways

Patent 11,274,332 is directed to genotype-specific treatment of LEMS with 3,4-DAP.
The core limitation is a human LEMS patient with two NAT2 slow alleles.
Claim 1 covers about 7.5-40 mg/day.
Claims 18 and 21 narrow the dose to about 7.5-15 mg/day and 15-30 mg/day.
Claim 24 specifically covers 3,4-DAP phosphate salt equivalent to about 7.5-30 mg/day.
Dependent claims cover specified NAT2 mutations, divided doses, scored 10 mg tablets, aqueous suspensions, and renal impairment.
The claims potentially overlap with genotype-directed Firdapse dosing but do not cover every Firdapse prescription.
Orange Book listing, patent expiration, Paragraph IV activity, and litigation status require review of current FDA, USPTO, and court records.
The principal commercial risk is a generic or compounded amifampridine regimen that uses the patented genotype-specific dosing instructions.

FAQs About US Patent 11,274,332

Does Patent 11,274,332 cover all patients with Lambert-Eaton myasthenic syndrome?

No. The claims require the patient to have two NAT2 slow alleles. Treatment of a LEMS patient without that genotype limitation is outside the literal scope of the supplied claims.

Does splitting a 10 mg amifampridine tablet create patent risk?

It can. Claims 5-7 specifically address divided dosing and scored tablets containing about 10 mg of 3,4-DAP or its salt equivalent, but the patient genotype and total daily dose limitations must also be satisfied.

Is an aqueous amifampridine suspension covered?

Claim 8 covers an aqueous suspension when it depends on the other limitations of claim 5 and claim 1. The suspension alone is not enough.

Can a generic company avoid the patent by using a different amifampridine salt?

Not necessarily. Claims 1, 18, and 21 cover pharmaceutically acceptable salts by equivalent 3,4-DAP dosing. Claim 24 separately identifies the phosphate salt, but a different salt may still fall within the broader salt language.

Does renal impairment independently trigger infringement?

No. Claim 17 requires renal impairment in addition to the limitations of claim 1, including LEMS, two NAT2 slow alleles, and the claimed daily dose.

References

U.S. Food and Drug Administration. (n.d.). Firdapse (amifampridine) prescribing information.
United States Patent and Trademark Office. (n.d.). Patent Center: U.S. Patent No. 11,274,332.
35 U.S.C. §§ 154, 156.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book.
21 C.F.R. § 314.94; 21 U.S.C. § 355(j).

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	11,274,332	⤷ 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: 11,274,332

Which drugs does patent 11,274,332 protect, and when does it expire?

Summary for Patent: 11,274,332