Details for Patent: 11,918,559

Which drugs does patent 11,918,559 protect, and when does it expire?

Patent 11,918,559 protects METAXALONE and is included in one NDA.

This patent has eight patent family members in six countries.

Summary for Patent: 11,918,559

Title:	Reduced dose metaxalone formulations
Abstract:	Oral dosage forms of metaxalone having improved bioavailability in the fed and fasted states, including dosage forms that employ a reduced dose based on such improved bioavailability.
Inventor(s):	Mukteeshwar Gande, Robert M. Levy
Assignee:	Primus Pharmceuticals Inc , PRIMUS PHARMACEUTICALS Inc
Application Number:	US18/197,100
Patent Claim Types: see list of patent claims	Composition; Formulation; Compound; Dosage form;

Scope and Claims Analysis for US Patent 11,918,559 (Metaxalone Micronized/Non-Micronized Particle-Graded Tablet with Propylene Glycol Alginate)

US Patent 11,918,559 claims a specific immediate-release solid oral tablet composition and manufacturing process for metaxalone that hinges on (i) a two-grade, particle-size–graded metaxalone blend (micronized “first grade” plus non-micronized “second grade”), (ii) inclusion of propylene glycol alginate and alginic acid (plus a narrow excipient set in dependent claims), (iii) hard numeric particle-size and sieving thresholds, and (iv) in some claims, in vivo bioequivalence criteria under fed and fasted conditions measured by AUC0-inf and Cmax-style peak ratio limits.

The patent landscape is likely dominated by three clusters of risk: (a) formulation/excipient and binding-matrix IP around propylene glycol alginate and alginic acid in immediate-release metaxalone tablets, (b) particle engineering IP (micronized/non-micronized metaxalone blend ratios and particle-size distributions with Malvern and sieve retention metrics), and (c) process IP for wet granulation plus controlled milling and magnesium stearate addition prior to compression.

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What does US 11,918,559 claim for metaxalone tablets: composition, particle grading, and bioequivalence?

Core independent claim (Claim 1): tablet + particle-grade metaxalone + propylene glycol alginate + self-bioequivalence

Claim 1 is the breadth anchor. It requires all of the following:

• Dosage form: “solid oral pharmaceutical tablet”
• Strength: 640 mg metaxalone (metaxalone-only weight is fixed at the claimed strength)
• Composition: metaxalone plus “one or more pharmaceutically acceptable excipients”
• Propylene glycol alginate presence: included at 10–30 weight parts (relative to the 640 mg metaxalone framework used in the claims)
• Metaxalone particle blend is central:
  • Metaxalone consists essentially of 40–80 wt% “first grade” particles and 20–60 wt% “second grade” particles
• First grade size specification: 90% of first grade < 100 microns by Malvern Method
• Second grade sieving specification: at least 35% retained on #120 sieve by “Sieve Method”
• In vivo performance requirement (bioequivalence to itself):
  • Must be bioequivalent under both fed and fasted conditions
  • Metric: AUC0-inf with 90% confidence interval for geometric mean test/reference
  • Peak concentration ratios constrained to 0.80–1.25

This is an “IP-hard” claim because it includes measurable physical parameters plus numeric pharmacokinetic endpoints.

Independent claim alternative (Claim 14): similar composition without propylene glycol alginate + different particle detail

Claim 14 has:

• Same tablet strength of 640 mg metaxalone
• Metaxalone split: 40–80 wt% first grade / 20–60 wt% second grade
• First grade: 90% < 100 microns (Malvern)
• Second grade: at least 35% retained on #120 sieve (sieve)
• No explicit propylene glycol alginate requirement is stated in Claim 14’s text as provided, but it still requires “one or more pharmaceutically acceptable excipients.”

Claim 14 therefore reads as composition breadth relative to Claim 1 (depending on how “excipients” are interpreted), while still keeping the metaxalone particle distribution strict.

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What are the narrower dependent claims that lock in particle cutoffs and formulation excipient set?

More restrictive particle-size windows (Claims 2, 10)

• Claim 2 tightens the particle specs:
  • First grade: 90% < 75 microns
  • Second grade: <5% retained on #30 sieve
• Claim 10 adds a tighter blend geometry:
  • Micronized/non-micronized: 40–80 wt% micronized and 20–60 wt% non-micronized
  • Micronized: 90% in 50–500 microns
  • Non-micronized: 2–10% retained on #30 and 25–45% retained on #120

These dependent claims materially increase infringement specificity: substituting a particle distribution that meets Claim 1 but not these windows can avoid these narrower claims, even while staying within the broader ones.

Micro vs non-micro composition and defined excipient scaffold (Claims 3, 6, 7, 8, 9, 11, 13)

Claim 3 defines an “oral dosage form” consisting essentially of:

• micronized metaxalone + non-micronized metaxalone
• propylene glycol alginate
• alginic acid

Claim 6 further locks excipients as:

• propylene glycol alginate: 10–30 weight parts
• lactose monohydrate: 20–35 weight parts
• alginic acid: 10–30 weight parts
• povidone: 40–60 weight parts
• magnesium stearate: 4–6 weight parts

Claim 7 is an extremely narrow quantitative excipient spec:

• povidone: 0.064–0.0212 w/w %
• lactose monohydrate: 0.0357 w/w %
• magnesium stearate: 0.00638 w/w %
• propylene glycol alginate: 0.021 w/w %
• alginic acid: 0.021 w/w %

(As written, the w/w ranges appear internally inconsistent in magnitude; practically, the legal scope will be interpreted against the patent’s full specification, but the literal language still narrows Claim 7 heavily.)

Claim 8: “further consisting essentially of 640 weight parts metaxalone” (i.e., the metaxalone amount is reiterated as fixed).

Claim 9: weight ratio micronized:non-micronized is 60:40 (a direct numeric ratio limitation).

Claim 11: composition consisting essentially of:

• 640 weight parts metaxalone
• 10–30 weight parts propylene glycol alginate

Claim 13: the tablet includes:

• 640 mg micronized and non-micronized metaxalone
• 10–30 propylene glycol alginate
• 10–30 alginic acid
• 4–6 magnesium stearate
• plus particle distribution constraints consistent with Claim 10-style tightened language:
  • metaxalone split 40–80 wt% / 20–60 wt% between first and second grade
  • 90% of micronized in 50–500 microns
  • non-micronized sieving: 2–10% on #30 and 25–45% on #120

Bioequivalence dependent performance (Claims 4 and 15)

• Claim 4: Claim 3 oral dosage form is “bioequivalent to itself under both fed and fasted conditions” with:
  • AUC0-inf geometric mean 90% CI
  • Cmax-style peak concentration ratio within 0.80–1.25
• Claim 15: same bioequivalence language paired with Claim 14’s particle distribution limits and independent claim structure.

These dependent claims make enforcement easier when the accused product can be tested to replicate the required PK endpoints.

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What manufacturing steps are claimed, and where do process variations create design-around paths? (Claim 12)

Claim 12 claims a tablet made by a defined wet-granulation process consisting essentially of:

1. Granulating solution: dissolve povidone in purified water by mixing
2. Pre-mix: pre-mix micronized and non-micronized metaxalone, propylene glycol alginate, and alginic acid at a suitable head speed
3. Wet granulation: wet granulate the pre-mix blend while adding the granulating solution
4. Drying: dry to predetermined moisture content
5. Commutation milling: mill the dried granulation product
6. Lubrication: mix magnesium stearate into the milled product
7. Compression: compress to tablet

A design-around is most realistic through changing the core process route (e.g., dry granulation, direct compression, fluid-bed granulation with different binder addition sequence, or different milling/conditioning controls) because Claim 12 is step-by-step rather than purely compositional.

However, Claim 12 is also “consisting essentially of,” leaving limited room for minor variations that don’t add steps or materials outside the claimed essentials.

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How is the claim scope likely interpreted: “consisting essentially of” vs “consisting of” and “grade” definitions?

“Consisting essentially of” broadens while still excluding key alternatives

Claims using “consisting essentially of” (e.g., Claim 3, 6, 12, 13) typically permit additional excipients/process aids that do not materially change the basic and novel characteristics. The novel characteristics here are anchored by:

• specific metaxalone particle distribution metrics (Malvern <100 or <75 microns; sieve retention thresholds),
• mandatory inclusion of propylene glycol alginate and alginic acid at least in the dependent cluster, and
• mandatory wet granulation with povidone solution and magnesium stearate prior to compression in process Claim 12.

“First grade” and “second grade” map onto measurable particle-size distributions

The claim text ties grades to quantitation methods:

• Malvern Method: percentage of first grade below a micron cutoff
• Sieve Method: percentage retained on #30/#120/#325 ranges

This structure means infringement turns on the accused product’s particle-size distribution testing under the recited methods (or at least substantially equivalent methods producing the same measured distributions).

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What is the competitive and litigation risk: how could generics and authorized entrants avoid these claims?

Likely avoidance vectors (from a litigation and product-development standpoint)

1. Alter the particle size distribution to miss thresholds
   • Changing Malvern distribution (e.g., ensure 90% is not <100 microns, or make it <100 but not within the micronized subranges that dependent claims require)
   • Changing sieve retention (e.g., reduce #120 retained fraction below 35% or push #30 retention outside 2–10% / <5% constraints)
2. Change the blend ratio
   • Avoid 60:40 micronized:non-micronized (Claim 9) and avoid out-of-range first/second grade percentages (40–80 / 20–60)
3. Swap excipient package
   • Avoid propylene glycol alginate inclusion where it is required (Claim 1 and many formulation claims)
   • Avoid alginic acid inclusion (Claim 3 and Claim 6/13 cluster)
4. Change process route
   • For Claim 12, move away from the defined sequence: povidone solution wet granulation + drying + comminution milling + Mg stearate mixing + compression

Where product “near-miss” designs are still risky

A tablet can avoid dependent claims 2/4/6/10/12/13/15 while still risking Claim 1 or Claim 14 if:

• it keeps the first/second grade particle constraints,
• includes propylene glycol alginate and uses the required blend percentages, and
• satisfies the PK “bioequivalence to itself” criteria.

Bioequivalence-to-itself language can be a practical hurdle for challengers because it creates an additional functional limitation that is harder to predict from in vitro tests alone.

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What broader patent landscape issues should be expected around this patent family theme?

Even without enumerating external patents in this response, the scope suggests the broader estate will cluster around:

1) Particle engineering IP for metaxalone

Expect filings covering:

• micronized vs non-micronized metaxalone procurement specifications,
• controlled milling and sieving controls,
• blending ratios and “two-grade” definitions, and
• method-of-measure claims (Malvern thresholds and sieve retention).

2) Excipient and matrix IP

Propylene glycol alginate and alginic acid are repeatedly central. The landscape likely includes:

• binder and disintegrant combinations,
• wet granulation binder systems (povidone),
• lubricant levels (magnesium stearate),
• lactose monohydrate interaction and granule formation controls.

3) Manufacturing process IP

Wet granulation plus defined drying/milling/compression steps is a common patent target. The claim text suggests protection of a specific sequence and material addition order.

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Key Takeaways

• US 11,918,559 protects a 640 mg metaxalone immediate-release tablet defined by two-grade particle-size distribution plus propylene glycol alginate and, in multiple claims, alginic acid.
• The claim set uses quantitative particle metrics: Malvern-based “% below X microns” and sieve-based “% retained on #120/#30/#325,” with multiple tight dependent cutoffs.
• Several claims add a functional limitation requiring fed and fasted self bioequivalence by AUC0-inf and peak ratio 0.80–1.25.
• A separate claim set protects a specific wet granulation process using povidone in purified water, addition sequence with PGO and alginic acid, post-drying comminution milling, Mg stearate mixing, then compression.
• Practical design-arounds concentrate on: particle-size distribution, micronized/non-micronized ratio, excipient substitution (PG alginate and/or alginic acid), and changing the process route away from the claimed wet granulation sequence.

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FAQs

1. Can a generic avoid infringement by only changing metaxalone particle size while keeping the same excipients?
   Yes, if it misses the Malvern and/or sieve retention thresholds required by the relevant claims.

2. Does Claim 12 require the exact same granulating solution composition and mixing order?
   Yes, the claim enumerates dissolving povidone in purified water, pre-mixing specific components, then wet granulating by adding that solution, followed by drying, comminution milling, Mg stearate mixing, and compression.

3. Are bioequivalence limitations enforceable even if the formulation is compositionally identical?
   Yes. Claims 4 and 15 require meeting defined fed/fasted AUC0-inf geometric mean 90% CI bioequivalence and peak ratio limits.

4. Which excipients are most critical across the claim set?
   Across dependent claims, the core excipient pair is propylene glycol alginate and alginic acid, with povidone and magnesium stearate appearing as key binder/lubricant elements in the narrower formulation and process claims.

5. Is changing the micronized-to-non-micronized ratio the most straightforward design-around?
   For claims that require a specific ratio (e.g., 60:40), it is a direct lever; for broader independent claims, ratio interacts with the required first/second grade weight percentages and particle constraints.

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References

1. US Patent 11,918,559 (claims as provided).

Drugs Protected by US Patent 11,918,559

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Primus Pharms	METAXALONE	metaxalone	TABLET;ORAL	022503-001	Jun 1, 2015		RX	Yes	Yes	11,918,559		Y

International Family Members for US Patent 11,918,559

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2020307390
Brazil	112021026371
European Patent Office	3989946
Japan	2022539368
Japan	2025169281
Japan	7791573
South Korea	20220025815