United States Patent 10,793,893: Claim Scope, Exclusivity, Litigation Risk, and 3,4-Diaminopyridine Patent Landscape

US 10,793,893 protects a pharmacogenomic dosing method for 3,4-diaminopyridine, also known as 3,4-DAP or amifampridine. The independent claim is limited to treating a human patient with a 3,4-DAP-sensitive disease who is a slow acetylator because of specified NAT2 mutations. The patent does not broadly cover all amifampridine treatment, all LEMS treatment, or all 3,4-DAP products.

The commercial significance is concentrated in Firdapse, Catalyst Pharmaceuticals’ amifampridine phosphate product for Lambert-Eaton myasthenic syndrome, or LEMS. The patent creates a potential method-of-use barrier for products administered to patients with the claimed NAT2 genotypes, but its practical enforcement value depends on whether manufacturers, prescribers, pharmacies, or patients can be shown to know and act on the genotype-specific treatment method.

What does US Patent 10,793,893 claim?

The patent’s independent claim requires every element below:

Claim element	Scope
Patient	Human patient
Disease	A diagnosed 3,4-DAP-sensitive disease requiring treatment
Active ingredient	3,4-DAP or a pharmaceutically acceptable salt
Dose	About 2.5 mg to about 30 mg
Pharmacogenomic status	Slow acetylator
NAT2 genotype	C282T on both alleles, T341C on both alleles, or C282T on one allele and T341C on the other allele

Claim 1 is therefore a genotype-selected treatment claim. It is narrower than a conventional claim covering amifampridine treatment of LEMS generally.

The dependent claims add disease, concentration, salt, dosing frequency, tablet, and daily-dose limitations. Claims 2 through 15 do not create independent inventions. Each remains subject to all limitations of claim 1.

How broad is the independent claim?

Claim 1 covers treatment of a defined subset of patients rather than the full patient population.

A potentially infringing treatment would need to satisfy four principal conditions:

The patient has a 3,4-DAP-sensitive disease.
The patient has one of the specified NAT2 genotypes.
The patient receives 3,4-DAP or an acceptable salt.
The administered dose falls within approximately 2.5 mg to approximately 30 mg.

The claim does not require:

A particular dosage form.
Oral administration.
A particular treatment duration.
A particular blood concentration.
A particular disease, because claims 2 and later specify diseases such as LEMS.
Genetic testing before treatment.
A specific commercial product.

The phrase “slow acetylator” is tied to the listed NAT2 genotypes. The claim is not written to cover every possible NAT2 slow-acetylator phenotype. It identifies three genotype configurations:

Genotype configuration in claim 1	Technical description
C282T on both alleles	Homozygous C282T
T341C on both alleles	Homozygous T341C
C282T on one allele and T341C on the other	Compound heterozygous configuration

The claim therefore excludes patients whose slow-acetylator status arises from other NAT2 variants unless those variants are legally treated as equivalent to the listed configurations.

What diseases are covered by US 10,793,893?

Claim 2 identifies three diseases:

Lambert-Eaton myasthenic syndrome.
Myasthenia gravis.
Congenital myasthenia.

The independent claim uses the broader phrase “3,4-DAP-sensitive disease.” The dependent claim narrows the scope to the three listed conditions. The commercial center of gravity is LEMS, because Firdapse is FDA-approved for LEMS in adults [2].

The patent does not, based on the supplied claims, cover treatment of every neuromuscular disease. A disease must either fall within the meaning of a 3,4-DAP-sensitive disease under claim 1 or satisfy one of the express disease limitations in claim 2.

What dosing regimens are protected?

The patent covers a wide dose range at the independent-claim level, followed by narrower daily-dose and administration limitations.

Claim	Dosing limitation
1	About 2.5 mg to about 30 mg
6	Dose is a total daily dose
7	One to five oral administrations per day
9	Scored tablet containing about 10 mg 3,4-DAP
10	Each single dose is about 5 mg to about 30 mg
11	Total daily dose is about 15 mg to about 30 mg
12	Total daily dose given in three or four doses
13	About 15 mg total daily dose in three doses
14	About 30 mg total daily dose in three doses
15	Total daily dose is about 7.5 mg to about 15 mg

The claims create overlapping dose ranges. For example, a patient receiving 15 mg per day in three doses may fall within claims 1, 6, 7, 11, 12, and 13, assuming the patient has the required NAT2 genotype and the other limitations are met.

The use of “about” expands the literal numerical boundaries to some degree, but it does not eliminate the need for a court to determine the relevant scope. The practical boundary will depend on intrinsic evidence, prosecution history, specification examples, and expert testimony.

Do the plasma-concentration claims add significant protection?

Claims 3 and 4 add pharmacokinetic limitations:

Claim 3 requires a maximum plasma concentration of about 90 ng/mL.
Claim 4 requires a maximum plasma concentration of about 15 ng/mL to about 40 ng/mL.

These claims are narrower than claim 1 because they require proof of a pharmacokinetic result after administration. They may be difficult to enforce without access to clinical pharmacology records, therapeutic drug monitoring, or a validated pharmacokinetic model.

Claim 3 is particularly important because “about 90 ng/mL” is a point-centered limitation rather than a broad concentration range. Claim 4 supplies a separate range. A product or treatment regimen may satisfy claim 1 without satisfying either plasma-concentration claim.

What formulation patents are implicated?

Claim 5 covers use of a pharmaceutically acceptable salt, including the phosphate salt. Claims 8 and 9 narrow the administration format to scored tablets, including a tablet containing about 10 mg of 3,4-DAP.

The formulation protection in US 10,793,893 is limited. The patent does not appear, from the supplied claims, to claim:

A complete tablet composition with specified excipients.
A particular dissolution profile.
A manufacturing process.
A particular polymorph.
A stability profile.
A capsule, liquid, injectable, or transdermal product.
A formulation independent of the NAT2-selected patient population.

The formulation limitations operate inside the genotype-specific treatment method. A scored 10 mg tablet is protected only when used in the claimed treatment of a qualifying slow acetylator.

How does US 10,793,893 relate to Firdapse?

Firdapse contains amifampridine phosphate and is approved in the United States for adults with LEMS [2]. The FDA label describes an initial dosage of 15 mg to 30 mg per day, administered in divided doses, with a maximum recommended total daily dosage of 80 mg [2].

That label creates substantial overlap with claims 1, 6, 7, 10, 11, 12, 13, and 14 for patients who have the specified NAT2 genotypes. The overlap is not complete because the patent requires a genotype-defined slow-acetylator population, while the FDA-approved label is not limited to that subgroup.

The patent therefore has two distinct commercial effects:

It may protect genotype-directed use of an existing amifampridine product.
It may not block ordinary, non-genotype-directed treatment of LEMS if the accused use cannot satisfy the genotype limitations.

What is the FDA and Orange Book status?

Firdapse was approved under NDA 208078 in November 2018 [2]. Amifampridine is a small-molecule drug, so biosimilar pathways under the Public Health Service Act do not apply. Competition would proceed through an abbreviated new drug application, or ANDA, if an applicant can rely on the applicable reference product and satisfy FDA requirements.

Orange Book protection must be analyzed patent by patent. A method-of-use patent may be listed if it claims an approved method of use and satisfies FDA listing requirements. The patent’s inclusion or exclusion from the Orange Book is not determined by the wording of the claims alone. The relevant records are the current FDA Approved Drug Products with Therapeutic Equivalence Evaluations database, FDA patent-listing submissions, and the NDA-specific patent information [3].

A listed method-of-use patent can produce a Paragraph IV certification and Hatch-Waxman litigation. If the patent is not listed, it may still support infringement litigation, but it generally will not generate the same automatic 30-month stay mechanism tied to an ANDA Paragraph IV notice.

When does US 10,793,893 lose exclusivity?

The patent term is generally measured from the earliest effective nonprovisional filing date, subject to patent-term adjustment, patent-term extension, terminal disclaimers, and other statutory rules [4]. The issued patent number and claim text alone do not establish the enforceable expiration date.

For commercial diligence, the relevant date must be taken from the USPTO patent record, including:

Earliest effective filing date.
Patent-term adjustment.
Any terminal disclaimer.
Patent-term extension under 35 U.S.C. § 156.
Maintenance-fee status.
Reexamination, reissue, or post-grant proceedings.

The patent’s expiration date should not be inferred solely from the FDA approval date. Regulatory exclusivity and patent exclusivity are separate.

Are there Paragraph IV challenges to this patent?

A Paragraph IV challenge is possible only if the patent is listed against the relevant reference product and an ANDA applicant certifies that the patent is invalid, unenforceable, or not infringed. The supplied claims do not establish whether an ANDA applicant has filed a Paragraph IV certification.

The principal potential Paragraph IV positions would include:

Potential position	Relevance
Lack of novelty	Prior art may disclose 3,4-DAP treatment but must disclose the claimed NAT2 genotype selection and dosing combination.
Obviousness	The challenger could combine known amifampridine treatment, NAT2 metabolism, and pharmacogenomic dosing evidence.
Written description	The challenger could argue that the specification did not adequately describe the full genotype and dose scope.
Enablement	The challenger could argue that the claims cover a broad patient and dosing range without sufficient guidance.
Indefiniteness	Terms such as “about,” “slow acetylator,” and “3,4-DAP-sensitive disease” could be examined in context.
Noninfringement	An ANDA label may omit the genotype-directed use or avoid instructions that encourage the claimed method.

The strongest noninfringement issue is likely the patient-genotype limitation. A generic label that merely describes amifampridine for LEMS may not necessarily instruct treatment of patients with the specific NAT2 configurations.

What patent litigation affects the patent?

The claim set creates several litigation questions:

Direct infringement

Direct method infringement generally requires performance of every claimed step. The patient receives the drug, but the commercial defendant may face liability under induced or contributory infringement theories if it promotes or supplies the product with knowledge that it will be used according to the patented method [5].

Induced infringement

Induced infringement risk increases if a product label, medical-information response, genetic-testing program, dosing guide, or promotional material instructs clinicians to identify NAT2 slow acetylators and administer the claimed dose.

A label that omits the genotype-specific method may reduce, but not automatically eliminate, inducement risk. Courts examine the totality of the evidence, including foreseeable use and affirmative instructions.

Proof of genotype

The patent owner would need evidence that the treated patient had one of the specified NAT2 genotypes. Routine treatment records may not contain that information. This creates a meaningful evidentiary barrier unless the accused company promotes genotype testing or maintains patient-genomic records.

Settlement agreements

No settlement terms can be inferred from the patent claims. Any ANDA settlement would need review of court dockets, consent judgments, FTC filings where applicable, and FDA patent records. A commercial settlement could establish an agreed generic-entry date without determining the ultimate validity of the patent.

How strong is the patent estate?

US 10,793,893 is strongest as a targeted method-of-use patent and weaker as a broad product barrier.

Estate characteristic	Assessment
Product coverage	Limited; claims require a specified patient genotype and dose
Disease coverage	Broad in claim 1, narrower in claim 2
Dose coverage	Meaningful overlap with approved Firdapse dosing
Formulation coverage	Narrow, mainly salt and scored-tablet limitations
Manufacturing coverage	None apparent from the supplied claims
Genetic testing dependence	High for proving infringement
Generic-label vulnerability	Material, depending on listed use and label wording
Biosimilar relevance	None; amifampridine is a small molecule
Geographic reach	United States only
Enforcement leverage	Higher against genotype-directed commercialization than ordinary LEMS treatment

The patent does not appear to block manufacturing of amifampridine outside the United States, nor does it create worldwide protection. Foreign counterparts must be analyzed separately by jurisdiction.

What generic-entry scenarios exist?

Three principal entry scenarios are relevant.

Scenario 1: Full-label generic entry

A generic applicant seeks approval for the same broad LEMS indication and challenges the listed patent under Paragraph IV. This creates the highest litigation exposure but also the clearest path to a court decision on validity and infringement.

Scenario 2: Carved-out labeling

The applicant removes or omits the genotype-specific method from its label under the section viii mechanism, where legally available. The resulting product may still be used by physicians for the patented method, but the sponsor would argue that the approved labeling does not induce infringement.

Scenario 3: Post-expiration entry

The applicant waits until patent expiration or an agreed launch date. This avoids immediate patent litigation but preserves the reference-product and regulatory barriers that remain in force.

Because the patent covers only a defined genetic subgroup, a carve-out strategy may be commercially attractive if the genotype-specific treatment is not a prominent part of the approved labeling or clinical practice.

How does this patent compare with broader amifampridine protection?

US 10,793,893 should be separated from patents claiming:

Amifampridine phosphate as a chemical or salt.
Specific crystalline or polymorphic forms.
Tablet compositions.
Manufacturing processes.
Broad methods of treating LEMS.
Pharmacokinetic dosing regimens.
Combination therapy.
Other patient subgroups.

A generic entrant must map each asserted patent independently. Avoiding this patent would not eliminate risk from a separate composition or formulation patent. Conversely, expiration or invalidation of a broader composition patent would not automatically eliminate the narrower NAT2 method claim.

Key Takeaways

US 10,793,893 is a genotype-specific method-of-treatment patent for 3,4-DAP.
Claim 1 requires one of three specified NAT2 mutation configurations, a qualifying disease, and a dose of approximately 2.5 mg to 30 mg.
Claims 2 through 15 narrow the invention to LEMS and related disorders, plasma concentrations, phosphate salt, oral divided dosing, scored tablets, and specified daily doses.
The patent overlaps with approved Firdapse dosing but does not broadly cover every use of amifampridine.
Its strongest commercial value is against genotype-directed prescribing, testing, labeling, or promotion.
Its principal enforcement weakness is the need to prove the patient’s NAT2 genotype and the defendant’s encouragement of the claimed treatment.
Biosimilar litigation is not relevant because amifampridine is a small-molecule drug.
Generic entry would likely involve a Paragraph IV challenge, a labeling carve-out, negotiated entry, or post-expiration launch.
Patent expiration must be determined from the USPTO term record, including patent-term adjustment and any terminal disclaimer.
The patent should be analyzed alongside separate composition, formulation, manufacturing, and method-of-use patents covering Firdapse.

FAQs

Does US 10,793,893 cover all Firdapse prescriptions?

No. The claims require treatment of patients with specified NAT2 genotypes. Ordinary Firdapse treatment without the claimed genotype limitation does not necessarily fall within the patent.

Can a generic amifampridine product avoid the patent by omitting NAT2 testing?

Potentially. Omission of genotype testing and genotype-specific instructions may support a noninfringement position, but it does not by itself resolve inducement or foreseeable-use issues.

Is the 10 mg scored tablet independently protected?

No. Claim 9 depends on claim 8, which depends on claim 7 and claim 6, all of which depend on claim 1. The 10 mg scored tablet limitation applies only within the claimed NAT2-selected treatment method.

Does the patent cover NAT2 variants other than C282T and T341C?

The supplied claims expressly identify C282T and T341C configurations. Other NAT2 variants are not expressly included in claim 1.

Does the patent create biosimilar exclusivity for Firdapse?

No. Firdapse contains the small molecule amifampridine phosphate. Any competitive FDA pathway would generally involve an ANDA or another small-molecule pathway, not a biosimilar application.

References

United States Patent No. 10,793,893, “Methods of treating 3,4-diaminopyridine sensitive diseases.” U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (2018). Firdapse (amifampridine) prescribing information. NDA 208078.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Orange Book.
United States Code. 35 U.S.C. §§ 154, 156, and 271.
United States Code. 21 U.S.C. § 355(j); 35 U.S.C. § 271(e).

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	10,793,893	⤷ 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

PCT Information
PCT Filed	June 29, 2012	PCT Application Number:	PCT/US2012/044904
PCT Publication Date:	January 03, 2013	PCT Publication Number:	WO2013/003708

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: 10,793,893

Which drugs does patent 10,793,893 protect, and when does it expire?

Summary for Patent: 10,793,893