United States Patent 9,918,973: Claim Scope, Dalfampridine Exclusivity, and Patent Landscape

U.S. Patent No. 9,918,973 protects a narrow method of treating multiple sclerosis with sustained-release 4-aminopyridine, marketed as dalfampridine extended release under the Ampyra brand. The claims require a 10 mg sustained-release dose administered twice daily, specified pharmacokinetic parameters, and improved walking speed in a human multiple sclerosis patient.

The patent is primarily a method-of-use and pharmacokinetic patent. It does not broadly cover all 4-aminopyridine formulations, all dalfampridine doses, or every treatment of multiple sclerosis. Its commercial value depends on whether a generic product meets the claimed dosing regimen and pharmacokinetic limitations, and whether the patent remains enforceable against an ANDA applicant.

What drug and product does U.S. Patent 9,918,973 cover?

U.S. Patent 9,918,973 covers sustained-release 4-aminopyridine, also called dalfampridine or fampridine. In the United States, the reference product is Ampyra extended-release tablets, manufactured and commercialized by Acorda Therapeutics.

The FDA-approved Ampyra regimen is:

Parameter	Ampyra reference product
Active ingredient	Dalfampridine, formerly 4-aminopyridine
Strength	10 mg
Dosage form	Extended-release tablet
Route	Oral
Frequency	Twice daily
Approximate interval	12 hours
Indication	Improvement of walking in adults with multiple sclerosis
Maximum labeled dose	10 mg every 12 hours
Titration	No titration required
Renal limitation	Contraindicated in moderate or severe renal impairment

The patent claims track the principal clinical and labeling characteristics of Ampyra. The claims also incorporate plasma concentration and time-to-maximum-concentration limitations that distinguish the claimed regimen from immediate-release 4-aminopyridine and from some alternative controlled-release products.

What are the independent claims in U.S. Patent 9,918,973?

Claims 1 and 7 are the two independent claims.

Claim 1: Single-dose pharmacokinetic limitation

Claim 1 requires all of the following:

A human multiple sclerosis patient in need of treatment.
Oral administration.
A sustained-release composition.
The composition contains 10 mg of 4-aminopyridine.
Administration occurs twice daily.
Treatment continues for at least two weeks.
Walking speed increases.
A single 10 mg administration produces a maximum observed plasma concentration of 27.7 ± 9.1 ng/mL.

The claim is therefore a treatment-method claim with a single-dose pharmacokinetic limitation. The claimed plasma range is approximately 18.6 to 36.8 ng/mL.

Claim 7: Steady-state pharmacokinetic limitation

Claim 7 has a similar structure but requires a steady-state exposure limitation:

A human multiple sclerosis patient in need of treatment.
Oral administration.
A sustained-release 10 mg 4-aminopyridine composition.
Twice-daily administration.
Treatment for at least two weeks.
Increased walking speed.
A steady-state maximum observed plasma concentration of 32.2 ± 8.9 ng/mL.

The steady-state plasma range is approximately 23.3 to 41.1 ng/mL.

Claims 1 and 7 are not interchangeable. A product or regimen could satisfy the steady-state limitation in claim 7 while failing the single-dose limitation in claim 1, or vice versa.

How do the dependent claims narrow the patent scope?

Claims 2 through 6 depend from claim 1. Claims 8 through 12 depend from claim 7.

Claims	Added limitation
2 and 8	Treatment continues for 12 weeks
3 and 9	Mean Tmax is approximately 2 to 5.2 hours
4 and 10	No prior or subsequent 4-aminopyridine titration
5 and 11	Administration occurs at 12-hour intervals
6 and 12	Sustained-release composition is a tablet

The dependent claims create narrower fallbacks. They are commercially relevant because the FDA-approved Ampyra label uses a tablet administered every 12 hours without titration. A generic product designed to be pharmaceutically equivalent to Ampyra would likely satisfy several of these limitations if it produces the claimed pharmacokinetic profile.

What is the full claim construction issue?

The patent’s infringement analysis turns on whether each limitation is met by the accused product and the proposed treatment method.

"Increasing walking speed"

The claims do not merely require administration of dalfampridine to an MS patient. They require that walking speed increase. The limitation links the drug regimen to a clinical result.

The Ampyra clinical program used walking performance, including the timed walk component of the Multiple Sclerosis Walking Scale and related ambulatory assessments. A plaintiff would likely rely on the product label, clinical-trial data, prescribing practice, and evidence that the drug is administered for its walking-improvement indication.

For a method-of-use claim, liability can depend on induced infringement. A generic manufacturer may face risk if its labeling, promotional materials, or regulatory submissions encourage use for the claimed walking-improvement indication.

"Sustained-release composition"

This limitation excludes ordinary immediate-release 4-aminopyridine products. It also raises a formulation question: whether the accused dosage form releases 4-aminopyridine over a period sufficient to produce the claimed exposure profile.

The claims do not require a particular excipient, coating, matrix, release mechanism, manufacturing process, or dissolution profile. The patent therefore has broader method coverage than a formulation claim, but its scope is constrained by the resulting plasma concentration and Tmax requirements.

"10 milligrams ... twice daily"

The claims require a 10 mg dose per administration, not merely 20 mg per day. A once-daily 20 mg product, a 5 mg tablet administered four times daily, or a variable-dose titration regimen would not literally meet this limitation.

The twice-daily requirement is reinforced by claims 5 and 11, which specify 12-hour intervals. The independent claims do not expressly require exact 12-hour spacing, but routine twice-daily administration could still be evidence of infringement depending on claim construction and prosecution history.

Pharmacokinetic limitations

The pharmacokinetic terms are central to the patent.

For claim 1, the single-dose maximum observed plasma concentration must fall within 27.7 ± 9.1 ng/mL. For claim 7, the steady-state maximum observed concentration must fall within 32.2 ± 8.9 ng/mL.

A generic sponsor could challenge these limitations by arguing that:

The reported ranges are indefinite.
The ranges describe population variability rather than a required product characteristic.
The values are not reliably reproducible between subjects.
The accused product does not consistently fall within the claimed range.
The claim requires a particular clinical study design or sampling methodology.
Pharmacokinetic variation prevents a finding that every administration meets the claimed range.

The patentee would respond that the ranges define measurable characteristics of the administered composition and that clinical pharmacokinetic testing can establish whether the product meets them.

What patent does U.S. 9,918,973 protect compared with formulation patents?

U.S. 9,918,973 is distinct from patents directed to the composition itself.

Protection type	Typical subject matter	Relevance to 9,918,973
Method-of-use	Treating MS patients to improve walking speed	Core protection
Pharmacokinetic method	Dose regimen producing specified Cmax or Tmax	Core protection
Formulation	Release matrix, excipients, coating, tablet structure	Separate patent category
Manufacturing	Granulation, compression, coating, or release-control process	Separate patent category
Labeling	Use for walking impairment in MS	Supports induced-infringement theories
Product-by-process	Product defined by manufacturing steps	Not apparent from the asserted claims

The patent does not, on its face, claim a specific polymer, coating, excipient, particle size, tablet hardness, dissolution profile, or manufacturing sequence. A competing formulation could avoid a formulation patent while still falling within the method claims if it is used at the claimed dose and produces the claimed pharmacokinetics.

What is the Orange Book status of U.S. Patent 9,918,973?

The patent has been associated with Ampyra’s U.S. patent estate and is relevant to FDA-approved dalfampridine extended-release products. Orange Book listing status must be assessed by product strength, dosage form, and the specific listing in the FDA publication in effect at the relevant time.

The key regulatory distinction is between:

A patent listed for the reference listed drug;
A patent certification made by an ANDA applicant;
A method-of-use patent carved out through a section viii statement; and
A patent that triggers a 30-month stay after a Paragraph IV notice.

For a method-of-use patent, an ANDA applicant may attempt a section viii statement if it proposes to omit the patented indication. That strategy is difficult where the patented use corresponds to the principal or only FDA-approved use of dalfampridine.

The FDA-approved indication for Ampyra is improvement of walking in adults with multiple sclerosis. That alignment makes a pure indication carve-out commercially and regulatory sensitive.

When does U.S. Patent 9,918,973 lose exclusivity?

The patent’s effective term depends on its earliest claimed priority date, patent-term adjustment, terminal disclaimers, and any applicable patent-term extension. Public patent records associate the Ampyra patent estate with expiration in the 2027 period, subject to the controlling USPTO term calculation and Orange Book entry.

Exclusivity component	Relevance
Patent term	Primary barrier associated with U.S. 9,918,973
FDA small-molecule exclusivity	Separate from patent term and generally shorter
Pediatric exclusivity	May add six months if granted and applicable
30-month ANDA stay	Litigation-related, not an extension of patent term
Settlement launch date	Contractual or litigation resolution date, which may precede patent expiration
Patent invalidity or noninfringement	Can remove practical enforcement before expiration

The patent issue date, March 20, 2018, does not determine the expiration date. U.S. utility patents generally expire 20 years from the earliest effective nonprovisional or international filing date, subject to statutory adjustments.

Which companies challenged the Ampyra patent estate?

Acorda’s Ampyra franchise attracted ANDA challenges from multiple generic manufacturers. Public litigation and settlement disclosures have involved companies including Roxane Laboratories, Mylan, Teva, Apotex, and other generic applicants.

The principal litigation issues in the Ampyra patent disputes included:

Obviousness of the sustained-release formulation;
Enablement and written description;
Infringement by proposed generic products;
Scope of the Orange Book-listed patents;
Section viii labeling strategies;
Settlement timing and authorized or licensed generic entry.

The Federal Circuit’s decision in Acorda Therapeutics, Inc. v. Roxane Laboratories, Inc. addressed Ampyra-related patent validity and obviousness issues. The decision illustrates the commercial importance of formulation development history and the relationship between the claimed release profile and the clinical product.

A Paragraph IV certification against U.S. 9,918,973 would require the applicant to assert that the patent is invalid, unenforceable, or not infringed. A timely patent-owner suit could trigger the statutory 30-month stay of FDA approval under the Hatch-Waxman Act, unless the litigation is resolved earlier or the stay is otherwise terminated.

How strong is the patent estate for dalfampridine?

The estate is stronger when evaluated as a portfolio rather than through U.S. 9,918,973 alone.

Strengths

The patent has several commercially favorable characteristics:

The dose and frequency align with the FDA-approved regimen.
The tablet and no-titration limitations correspond to the reference product.
The indication is the core approved use of Ampyra.
The pharmacokinetic values can be tested through ANDA bioequivalence and pharmacokinetic studies.
A generic product may have difficulty omitting the walking-improvement use while remaining commercially viable.

Vulnerabilities

The patent also has material litigation vulnerabilities:

The claims combine clinical-effect limitations with pharmacokinetic ranges.
Pharmacokinetic variability can complicate infringement proof.
Earlier 4-aminopyridine literature may support obviousness arguments.
Sustained-release formulations and twice-daily dosing may be characterized as predictable design choices.
A generic applicant may argue that the claimed plasma ranges are inherent or routinely optimized.
The patent may be vulnerable if the specification does not adequately support every claimed range and clinical outcome.

The strongest enforcement case would likely involve a generic label that expressly directs use of 10 mg extended-release dalfampridine twice daily for improved walking in MS patients, together with pharmacokinetic data falling within the claimed ranges.

What generic launch scenarios exist?

Scenario 1: Launch after patent expiration

This is the lowest-risk scenario. The generic launches after the relevant patent term ends and after FDA approval becomes effective.

Scenario 2: Settlement-based launch

The generic company receives a licensed entry date under a settlement agreement. Entry can occur before the nominal patent expiration if the agreement permits it.

Scenario 3: At-risk launch

The generic launches before final resolution of the patent litigation. The manufacturer accepts potential damages, an injunction, and regulatory disruption if the patent is upheld.

Scenario 4: Label carve-out

The generic removes the patented method from its label. This strategy is more difficult for dalfampridine because improved walking in MS is the central approved use.

Scenario 5: Non-infringing pharmacokinetic profile

The applicant argues that its product does not produce the claimed Cmax or Tmax values. This approach would require persuasive comparative pharmacokinetic evidence and may create regulatory or substitution complications.

How does U.S. 9,918,973 compare with competing dalfampridine protections?

Issue	U.S. 9,918,973	Formulation patent	Manufacturing patent
Primary subject	Treatment method	Tablet or release system	Production process
Required dose	10 mg	May vary	Usually not central
Required frequency	Twice daily	Product-dependent	Not central
Clinical result	Increased walking speed	Not required	Not required
PK limitations	Yes	May be indirect	Usually no
Tablet limitation	Dependent claims	Often central	Not central
Indication risk	High	Lower if use is omitted	Lower
Primary challenge	Invalidity or noninfringement	Obviousness and claim scope	Process nonuse

A successful challenge to U.S. 9,918,973 would not necessarily eliminate all Ampyra-related patent risk. A generic company must evaluate separate formulation, manufacturing, and method-of-use patents, as well as regulatory exclusivity and settlement restrictions.

What geographic coverage does the patent provide?

U.S. Patent 9,918,973 provides rights only in the United States. It does not directly block dalfampridine products in Canada, Europe, Japan, or other jurisdictions.

International coverage depends on corresponding national patents and their prosecution outcomes. The relevant commercial questions are:

Whether a counterpart patent issued in the target country;
Whether the claims cover the same 10 mg twice-daily regimen;
Whether the national patent includes pharmacokinetic limitations;
Whether supplementary protection or patent-term restoration applies;
Whether local regulatory data exclusivity remains active.

In Europe, the active ingredient is commonly referred to as fampridine, and the regulatory and patent analysis may differ from the U.S. dalfampridine framework.

What manufacturing and IP barriers affect generic entry?

The principal technical barrier is reproducing a sustained-release product with a comparable exposure profile. A generic sponsor must address:

Release kinetics over the dosing interval;
Cmax and Tmax;
Steady-state exposure;
Food effects;
Tablet integrity and dose uniformity;
Renal impairment warnings;
Bioequivalence requirements;
Potential design-around of formulation patents.

A generic can potentially avoid literal infringement by changing the release mechanism or producing a pharmacokinetic profile outside the claimed ranges. That approach may be difficult if FDA requirements for pharmaceutical equivalence and bioequivalence effectively constrain the product toward the reference profile.

What is the commercial exposure from Ampyra patent risk?

Ampyra was a significant commercial product for Acorda, and generic competition materially affected the company’s revenue base after generic dalfampridine approvals. The relevant exposure is concentrated in:

U.S. net sales of Ampyra;
Royalty or licensing income;
Manufacturing arrangements;
Distribution contracts;
Settlement-related launch restrictions;
Post-expiration price erosion.

Revenue risk is not limited to the expiration date. An at-risk generic launch, an authorized generic, or a settlement permitting early entry can reduce branded sales before formal patent expiration.

Key Takeaways

U.S. Patent 9,918,973 is a method-of-use and pharmacokinetic patent covering sustained-release 10 mg 4-aminopyridine administered twice daily to improve walking in MS patients.
Claims 1 and 7 differ primarily in the pharmacokinetic endpoint: single-dose Cmax versus steady-state Cmax.
The dependent claims add 12-week treatment, 2-to-5.2-hour Tmax, no titration, 12-hour intervals, and tablet form.
The patent closely tracks the FDA-approved Ampyra regimen, increasing potential induced-infringement risk for a generic using the full MS walking-improvement indication.
The patent does not broadly claim every dalfampridine formulation or manufacturing process.
Generic challenges are likely to focus on obviousness, written description, enablement, pharmacokinetic claim interpretation, and noninfringement.
Patent expiration is associated with the 2027 period, subject to the controlling USPTO term calculation, Orange Book listing, patent adjustments, and any settlement-based entry date.
A challenge to U.S. 9,918,973 would not automatically eliminate separate formulation or manufacturing patent risks.

FAQs

Does U.S. Patent 9,918,973 cover immediate-release 4-aminopyridine?

No. The claims require a sustained-release composition. An immediate-release product would not literally satisfy that limitation.

Can a generic sell dalfampridine without infringing the patent?

Potentially, but the answer depends on the proposed label, dose, frequency, formulation, pharmacokinetic profile, and litigation outcome. A product that mirrors Ampyra’s 10 mg twice-daily MS walking indication faces the highest risk.

Does the patent require exactly 12-hour dosing?

The independent claims require twice-daily administration. Claims 5 and 11 expressly require 12-hour intervals. Exact 12-hour dosing is therefore a limitation of the narrower dependent claims, not expressly of claims 1 and 7.

Is the patent a formulation patent?

No. It is principally a method-of-use patent with pharmacokinetic limitations. The tablet limitation appears only in dependent claims 6 and 12.

Does a Paragraph IV challenge immediately invalidate the patent?

No. A Paragraph IV certification is an ANDA applicant’s legal position that the patent is invalid, unenforceable, or not infringed. The patent remains enforceable unless a court invalidates it, finds noninfringement or unenforceability, or the patent expires.

References

Acorda Therapeutics, Inc. (2018). AMPYRA (dalfampridine) extended-release tablets, prescribing information. U.S. Food and Drug Administration.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
United States Patent and Trademark Office. (2018). U.S. Patent No. 9,918,973: Methods of treating multiple sclerosis. U.S. Department of Commerce.
Acorda Therapeutics, Inc. v. Roxane Laboratories, Inc., 903 F.3d 1310 (Fed. Cir. 2018).
U.S. Food and Drug Administration. (1984). Drug Price Competition and Patent Term Restoration Act of 1984. 21 U.S.C. § 355(j).
U.S. Patent and Trademark Office. (2024). Patent term adjustment and patent term calculation guidance. U.S. Department of Commerce.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	1732548	⤷ Start Trial	C300515	Netherlands	⤷ Start Trial
European Patent Office	1732548	⤷ Start Trial	PA2012001	Lithuania	⤷ Start Trial
European Patent Office	1732548	⤷ Start Trial	CA 2012 00004	Denmark	⤷ Start Trial
European Patent Office	1732548	⤷ Start Trial	C20120002 00051	Estonia	⤷ Start Trial
European Patent Office	1732548	⤷ Start Trial	PA2012001,C1732548	Lithuania	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 9,918,973