US Patent 11,857,547: Nalmefene Magnesium-Chloride Formulation Claims, Expiration, and Patent Landscape

US Patent 11,857,547 protects a specific injectable nalmefene formulation, not nalmefene generally. Its core combination is an aqueous parenteral product containing approximately 1.5 mg nalmefene free base equivalent and 0.5% to 1.0% w/v magnesium chloride. The patent also requires a pharmacokinetic result: the formulation must produce a shorter mean Tmax than a comparator without magnesium chloride after intramuscular or subcutaneous administration.

The commercially important embodiment is claim 7: approximately 1.5 mg nalmefene hydrochloride, equivalent to 1.5 mg nalmefene free base, with approximately 0.9% w/v magnesium chloride, administered intramuscularly. The patent therefore presents a formulation and regulatory-barrier risk for competing injectable nalmefene products, while leaving nasal formulations, non-magnesium adjuvants, and many alternative dosage strengths outside the literal claim scope.

What does US Patent 11,857,547 protect?

US 11,857,547 protects a parenteral aqueous nalmefene formulation containing magnesium chloride at a defined concentration and producing a shorter mean time to maximum plasma concentration than a no-adjuvant comparator.[1]

Claim element	Scope under the issued claims
Active ingredient	Nalmefene free base or a pharmaceutically acceptable salt
Dose	About 1.5 mg nalmefene free base equivalent
Dosage form	Aqueous parenteral solution
Administration	Intramuscular or subcutaneous injection
Adjuvant	Magnesium chloride
Adjuvant concentration	About 0.5% to about 1.0% w/v
Pharmacokinetic limitation	Mean nalmefene Tmax must be shorter than the comparator without the adjuvant
Preferred salt	Nalmefene hydrochloride
Preferred concentration	About 0.9% w/v magnesium chloride
Preferred route in claim 7	Intramuscular injection

The patent does not claim every nalmefene injection. A formulation that lacks magnesium chloride, falls outside the claimed concentration range, uses a materially different nalmefene dose, or fails the claimed Tmax comparison may avoid literal infringement.

How do the seven issued claims differ?

Claim 1 is the principal composition and performance claim. It requires:

An aqueous parenteral formulation.
Approximately 1.5 mg nalmefene free base or an equivalent salt amount.
Approximately 0.5% to 1.0% w/v of a parenterally acceptable adjuvant.
A shorter mean Tmax than a no-adjuvant comparator.
Magnesium chloride as the adjuvant.

The adjuvant language initially appears broad, but the final limitation restricts the claim to magnesium chloride. A formulation using sodium chloride, calcium chloride, another magnesium salt, or a non-electrolyte absorption-enhancing excipient would not satisfy the claim as written unless the accused product also contains magnesium chloride.

Claim 2 narrows claim 1 by requiring a stated relative Tmax improvement of approximately 1.1-fold, 1.2-fold, or 1.3-fold. The phrase “times shorter” creates an interpretation issue because pharmacokinetic comparisons are normally expressed as a ratio or percentage reduction. An infringement dispute would likely focus on whether the claim means:

comparator Tmax divided by inventive-formulation Tmax; or
percentage shortening relative to the comparator.

Claim 3 narrows the magnesium chloride concentration to approximately 0.9% w/v. This is the most commercially significant concentration claim because it corresponds to the principal formulation described in the user-provided claims.

Claim 4 specifies nalmefene hydrochloride in an amount equivalent to 1.5 mg nalmefene free base. It removes ambiguity between free-base dosing and salt mass.

Claims 5 and 6 separately specify intramuscular and subcutaneous administration. They are narrower than claim 1 in route but may be easier to apply against a product approved or marketed for one defined route.

Claim 7 is a consolidated, highly specific intramuscular formulation claim. It requires nalmefene hydrochloride, the 1.5 mg free-base equivalent dose, approximately 0.9% w/v magnesium chloride, and the shorter-Tmax result.

What is the technical inventive concept?

The patent’s technical concept is pharmacokinetic acceleration through magnesium chloride in an injectable nalmefene solution. The claimed benefit is a shorter Tmax, meaning earlier attainment of peak plasma nalmefene concentration after injection.

The patent does not rely only on ingredient identity. It combines composition limitations with a functional pharmacokinetic limitation. That structure has two consequences:

A competitor may need to test the accused formulation in a comparative clinical or pharmacokinetic study.
The patentee may argue that a formulation falls within the claim even if its label does not expressly describe the Tmax effect, provided the product inherently produces the claimed result.

The comparator is central. The claims compare the magnesium-containing formulation with a formulation without the adjuvant. Questions likely to matter in litigation include:

Whether the comparator must be otherwise compositionally identical.
Whether the comparator must use the same dose and route.
Whether the subjects must be matched for sex, body weight, injection site, and opioid status.
Whether the mean Tmax difference must be statistically significant.
Whether the claimed result must occur in every subject or only in the population mean.
Whether “about” permits variation around 1.5 mg and the stated concentration range.

What formulations are protected by US 11,857,547?

The strongest literal-read infringement scenario is an aqueous nalmefene hydrochloride injection containing approximately 1.5 mg free-base equivalent and approximately 0.9% w/v magnesium chloride.

Formulation configuration	Likely relationship to claim scope
Nalmefene HCl, 1.5 mg free-base equivalent, 0.9% magnesium chloride	Core claimed embodiment
Nalmefene HCl, 1.5 mg free-base equivalent, 0.5% magnesium chloride	Within claim 1 if the Tmax limitation is met
Nalmefene HCl, 1.5 mg free-base equivalent, 1.0% magnesium chloride	Within claim 1 if the Tmax limitation is met
Nalmefene HCl without magnesium chloride	Outside literal claim 1
Nalmefene HCl with sodium chloride only	Outside literal claim 1
Nalmefene free base with magnesium chloride	Potentially within claim 1
Nalmefene salt at a materially different free-base equivalent dose	Potentially outside the dose limitation
Nalmefene nasal spray	Outside the parenteral-solution limitation
Nalmefene implant or oral dosage form	Outside the claimed dosage-form scope
Injectable nalmefene with magnesium chloride outside the claimed range	Potentially outside literal scope, subject to “about” interpretation

The patent does not expressly claim an auto-injector, needle assembly, container, cartridge, device control system, or packaging configuration. Those aspects may be covered by separate device or delivery patents.

When does US Patent 11,857,547 expire?

The patent has a nominal 20-year term measured from the relevant US nonprovisional filing or applicable priority framework. Public patent records identify a 2021 US filing and a 2020 priority date for the nalmefene formulation disclosure.[1]

The expected nominal term runs into 2041, subject to patent-term adjustment, terminal disclaimers, patent-term extension, or other USPTO determinations. The precise enforceable expiration date should be taken from the current USPTO Patent Center record and the patent’s face-page term data before making a launch decision.

Event	Publicly relevant timing
Earliest identified priority period	2020
US filing period	2021
Patent grant	January 2, 2024
Patent number	US 11,857,547
Expected nominal expiration window	2041
Regulatory exclusivity effect	Separate from patent term

FDA approval does not extend the patent automatically. Conversely, FDA exclusivity does not change the patent expiration date.

What is the FDA and Orange Book status of nalmefene products?

Nalmefene is an opioid antagonist related to naloxone. The FDA has approved nalmefene products through different routes and product configurations, including injectable and nasal products. FDA-approved product status must be assessed by NDA, dosage form, route, strength, and proprietary product rather than by active ingredient alone.[2]

The Orange Book may list patents for an approved drug product if the NDA holder submits eligible patent information and FDA accepts the listing. A listed formulation patent can create a 30-month stay when an ANDA applicant submits a valid Paragraph IV certification and the NDA holder timely sues. The stay mechanism applies to ANDAs, not to all forms of competition.[3]

Patent 11,857,547 is most relevant to an approved injectable nalmefene product matching the claimed 1.5 mg and magnesium-chloride formulation. It is less directly relevant to:

Nalmefene nasal spray products.
Different injectable strengths.
Products using a different excipient system.
505(b)(2) products that do not rely on an identical listed formulation.
Products with a different route or delivery technology.

The Orange Book listing status should be confirmed against the current FDA Orange Book patent table for the specific nalmefene NDA. A patent can be enforceable even when it is not listed, but an unlisted patent does not ordinarily create the same ANDA certification and automatic-stay pathway.

What Paragraph IV challenges and generic entry risks exist?

A generic or follow-on injectable applicant could challenge the patent through a Paragraph IV certification if the patent is listed against the relevant reference product. The principal attack routes would likely include:

Lack of written description or enablement

The claims cover a defined concentration range and require a population-level Tmax result. A challenger could argue that the specification does not adequately support the full range, all pharmaceutically acceptable nalmefene salts, both injection routes, and all claimed levels of Tmax shortening.

Indefiniteness

The phrases “about 1.5 mg,” “about 0.5% to about 1.0%,” “about 1.1 times shorter,” and “population of subjects” may generate claim-construction disputes. The phrase “times shorter” is particularly vulnerable if the specification does not define the calculation.

Anticipation

An earlier reference could defeat the patent if it discloses the complete combination of nalmefene, magnesium chloride, the claimed concentration, dose, injectable aqueous formulation, and the required Tmax result.

Obviousness

A challenger could combine prior art relating to:

Nalmefene injectable dosage forms.
Magnesium chloride or electrolyte excipients.
Injection-site absorption.
Pharmacokinetic acceleration.
Nalmefene hydrochloride dosing.
Comparable opioid-antagonist formulations.

The patent’s best defense would be evidence that the specific magnesium chloride concentration produced an unexpected Tmax improvement or solved a recognized absorption problem.

Inherent infringement and inherent anticipation

Because the claims include a pharmacokinetic result, parties may dispute whether the result is inherent in a formulation. The patentee may rely on testing showing that a competing product necessarily produces the shorter Tmax. The challenger may argue that the result depends on clinical conditions not fixed by the claim.

How strong is the patent estate for injectable nalmefene?

Patent 11,857,547 has moderate-to-strong commercial relevance for an exact-match injectable formulation and more limited blocking power across the broader nalmefene market.

Risk category	Assessment
Exact 1.5 mg nalmefene HCl plus 0.9% magnesium chloride injection	High
Same dose with magnesium chloride within 0.5%-1.0% range	High if Tmax limitation is met
Same dose without magnesium chloride	Lower under literal claim scope
Alternative magnesium salt	Lower, subject to equivalents analysis
Different injectable strength	Lower, unless “about” captures the strength
Nalmefene nasal spray	Low under this patent
Auto-injector hardware	Not claimed expressly
Manufacturing process	Not claimed expressly
Formulation performance testing	Important to both infringement and validity
ANDA risk	Depends on Orange Book listing and reference-product identity

The patent is narrower than a conventional composition-of-matter patent. Its value depends on the commercial product’s exact composition and the ability to demonstrate the claimed pharmacokinetic result.

What patent litigation affects US 11,857,547?

The supplied record identifies the issued claims but does not establish a reported district-court infringement action, Paragraph IV complaint, or settlement involving US 11,857,547. The patent should therefore be treated as an issued exclusion right with litigation potential, not as a patent with a confirmed adverse judgment or settlement.

A transaction or launch review should distinguish among:

Patent issuance.
Orange Book listing.
Paragraph IV notice.
Filing of an infringement action.
A 30-month stay.
Settlement or license.
Final judgment.
Appeal.

These events have different commercial consequences. Patent issuance alone does not prove that an ANDA challenge exists, and the absence of a publicly identified case does not eliminate future litigation risk.

Are there biosimilar risks for nalmefene?

No conventional biosimilar pathway applies. Nalmefene is a chemically synthesized small molecule, not a biologic subject to the Public Health Service Act biosimilar framework. Competitive products would generally proceed through an ANDA, a 505(b)(2) application, or a full NDA depending on formulation, route, labeling, and reliance on the reference product.[3]

For this patent, the more relevant competitors are:

ANDA applicants seeking approval of an equivalent injectable product.
505(b)(2) applicants using a modified formulation or delivery system.
NDA sponsors developing alternative injectable or nasal nalmefene products.
Device companies pairing nalmefene with a novel autoinjector.

What licensing deals and ownership issues matter?

The patent’s commercial value depends on the relationship among the patent owner, NDA holder, product marketer, and device developer. A patent assignment, exclusive license, field-of-use license, or acquisition can alter who has standing to sue and who controls regulatory enforcement.

Public patent records identify the applicant or assignee associated with the patent record, while FDA records identify the NDA holder. Those entities are not necessarily identical. Ownership and enforcement authority should therefore be checked through:

USPTO assignment records.
FDA NDA and Orange Book records.
SEC filings of publicly traded parties.
Acquisition agreements.
License and commercialization disclosures.

No confirmed public settlement or license specific to US 11,857,547 is established by the claim record supplied here.

How does US 11,857,547 compare with nalmefene nasal-spray patents?

The patent has a different technical and commercial focus from nasal nalmefene patents. US 11,857,547 addresses injectable pharmacokinetics and magnesium chloride. Nasal-spray patents generally focus on intranasal delivery, spray devices, nasal absorption, dose uniformity, formulation viscosity, or actuator design.

Issue	US 11,857,547	Nasal nalmefene patent families
Route	Intramuscular or subcutaneous	Intranasal
Dosage form	Aqueous parenteral solution	Nasal spray
Key excipient	Magnesium chloride	May include buffers, surfactants, preservatives, or absorption enhancers
Main performance metric	Shorter Tmax after injection	Nasal deposition, absorption, or systemic exposure
Product overlap	Injectable nalmefene	Nasal nalmefene
Biosimilar relevance	None	None
Primary approval pathway	NDA, ANDA, or 505(b)(2) depending on product	NDA or 505(b)(2), depending on reliance

A nasal product would ordinarily not infringe the claims merely because it contains nalmefene and achieves rapid systemic exposure.

What generic launch scenarios are most credible?

Scenario 1: Exact-match injectable

A competitor copies the 1.5 mg nalmefene hydrochloride formulation with approximately 0.9% magnesium chloride. This presents the highest infringement risk and would likely require a Paragraph IV strategy if the patent is listed.

Scenario 2: Magnesium-free injectable

A competitor develops an injectable without magnesium chloride. This may avoid literal infringement but must still address other patents, regulatory equivalence, injection-site tolerability, pharmacokinetics, and any doctrine-of-equivalents argument.

Scenario 3: Alternative excipient system

A competitor uses another absorption-modifying excipient or a different magnesium salt. Literal exposure is lower, but the formulation may face separate patent claims and formulation-development risks.

Scenario 4: Modified dose or route

A different strength, subcutaneous-only product, or alternative presentation may avoid some dependent claims. It would not necessarily avoid claim 1 if the product remains within the “about” ranges and satisfies the functional limitation.

Scenario 5: 505(b)(2) product

A sponsor may pursue a modified injectable or delivery system under section 505(b)(2). This route can reduce development duplication but does not eliminate patent litigation or certification obligations.

Key Takeaways

US 11,857,547 is a formulation patent, not a broad nalmefene composition-of-matter patent.
The core protected combination is approximately 1.5 mg nalmefene free-base equivalent, magnesium chloride at approximately 0.5% to 1.0% w/v, and a shorter mean Tmax than a no-adjuvant comparator.
Claim 7 is the narrowest and most commercially targeted claim: nalmefene hydrochloride, approximately 0.9% magnesium chloride, and intramuscular administration.
The patent does not expressly claim nasal sprays, autoinjector hardware, manufacturing processes, or nalmefene generally.
The principal validity issues are likely to involve obviousness, enablement, written description, indefiniteness, and the meaning of the Tmax comparison.
The expected patent term extends into 2041, subject to USPTO term calculations and any adjustment.
Generic risk depends heavily on whether the patent is listed in the Orange Book for the relevant injectable nalmefene NDA.
Nalmefene has no biosimilar pathway because it is a small molecule.
A magnesium-free or differently dosed injectable is the clearest design-around direction, but it may encounter separate patents and regulatory barriers.

FAQs About US Patent 11,857,547

Does US 11,857,547 cover nalmefene hydrochloride by itself?

No. The claims require a specific parenteral aqueous formulation, a defined dose range, magnesium chloride, and the shorter-Tmax limitation.

Does the patent cover a nalmefene injection containing sodium chloride instead of magnesium chloride?

Not literally under the issued claims provided. The claims specify magnesium chloride as the adjuvant.

Can a competitor avoid the patent by changing 0.9% magnesium chloride to 1.1%?

Possibly, but not automatically. The competitor would need to assess whether 1.1% falls within the ordinary meaning of “about” and whether other claims or the doctrine of equivalents create exposure.

Is an intranasal nalmefene product blocked by this patent?

The issued claims provided are directed to parenteral formulations and intramuscular or subcutaneous injection. An intranasal product would generally fall outside those limitations.

Does patent expiration end FDA exclusivity at the same time?

No. Patent term and FDA regulatory exclusivity are separate rights with separate expiration rules.

References

United States Patent and Trademark Office. (2024). US Patent No. 11,857,547, nalmefene formulations. USPTO Patent Center and Google Patents records.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs database. https://www.accessdata.fda.gov/scripts/cder/daf/
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Knoa Pharma	ZURNAI (AUTOINJECTOR)	nalmefene hydrochloride	SOLUTION;INTRAMUSCULAR, SUBCUTANEOUS	218590-001	Aug 7, 2024		RX	Yes	Yes	11,857,547	⤷ Start Trial	Y				⤷ 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
Australia	2019376633	⤷ Start Trial
Australia	2025267445	⤷ Start Trial
Canada	3118708	⤷ Start Trial
European Patent Office	3876938	⤷ Start Trial
Japan	2022516595	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 11,857,547

Which drugs does patent 11,857,547 protect, and when does it expire?

Summary for Patent: 11,857,547