US Patent 8,901,173 (GHB salt-mixture compositions): scope, claim boundaries, and US patent landscape

US 8,901,173 claims a narrow but operational composition strategy for gamma-hydroxybutyrate (GHB): a liquid, preservative-free pharmaceutical composition made from a mixture of GHB salts (Na.GHB, K.GHB, Mg.(GHB)2, Ca.(GHB)2), with defined weight-percent ranges/ratios and defined aqueous concentration and pH windows. The estate is composition-centric (not method-of-treatment) and is likely to be enforced against (i) specific salt combinations, (ii) specific relative proportions, and (iii) specific solution conditions that support chemical stability and microbial resistance without preservatives.

What does US 8,901,173 claim for GHB salt mixtures, and what is the core invention?

Short answer: The core claim scope is a pharmaceutical composition containing three or more specific GHB salts from a defined list, with aqueous liquid embodiments at 250–750 mg/mL total GHB mixture (claim 21/30/31), pH ~7.0–9.0 (claim 21), preservative-free, and optionally specific pH-adjusting acids such as malic acid (claims 23–26). The composition can be used in liquid form and is suitable for oral administration (claims 27–29).

Core claim (Claim 1): “mixture of salts” definition controls infringement

Claim 1 requires:

A pharmaceutical composition of GHB comprising a mixture of salts of GHB
The mixture comprises three or more salts
The salts are selected from:
- Na.GHB (sodium gamma-hydroxybutyrate)
- K.GHB (potassium gamma-hydroxybutyrate)
- Mg.(GHB)2 (magnesium bis(gamma-hydroxybutyrate))
- Ca.(GHB)2 (calcium bis(gamma-hydroxybutyrate))

This is a classic “closed Markush list” for the salt types, but it is open on the count (“three or more”).

Claim 1 scope boundary: products using only one or two salt species from the list fall outside. Products using additional salt types beyond the list are not covered by Claim 1 unless those additional salts are still within the Markush structure as “selected from” the group (Claim 1 reads as only those salts are part of the mixture; if extraneous salts of GHB were used that are not in the enumerated group, coverage is likely lost).

Dependent claims (2–20) narrow to specific salt sets and proportion windows

Claim 2: mixture includes Na.GHB, K.GHB, Mg.(GHB)2, Ca.(GHB)2 (all four).
Claims 3–10: specify wt/wt % ranges for each salt in the all-four embodiment.
Claims 11–14: broaden to “overall ranges” plus ratio examples (still within the four-salt set).
Claims 15–17: subset with Na.GHB, K.GHB, Ca.(GHB)2 only.
Claims 18–20: subset with K.GHB, Mg.(GHB)2, Ca.(GHB)2 only.

Business meaning: infringement analysis will hinge on measured salt composition in the final formulation (wt/wt of each salt) and whether the product contains the required number of salt species and the required ranges/ratios.

Liquid/pH stability/preservative-free embodiments (21–33) drive practical detectability

Claim 21: aqueous solution of ~250–750 mg/mL of the salt mixture, with pH ~7.0–9.0, chemically stable, resistant to microbial growth, and free of preservatives.
Claim 22: pH ~7.3–8.5.
Claims 23–26: may include a pH adjusting/buffering agent that can be an acid, including a list of acids; malic acid is explicitly recited (claim 26).
Claims 27–31: formulation is a liquid, chemically stable, microbial-resistant, preservative-free, suitable for oral administration, with GHB concentration between:
- Claim 30: 300–750 mg/mL
- Claim 31: 400–600 mg/mL
Claim 32: optional carriers/excipients plus a broad list of auxiliary categories, including antibacterial/antifungal agents.
Claim 33: “molecular weight per oxybate equivalent” is about the same as sodium oxybate (tie to sodium oxybate equivalence).

Practical consequence: If the accused product is a liquid oxybate-class formulation, the strongest enforcement theory is typically claim 21 plus the salt composition ranges plus preservative status plus pH and concentration.

Which salt combinations and wt/wt ratios are explicitly covered by the claims?

A. Four-salt mixture (Na, K, Mg, Ca all present)

Claim 2 requires all four salts. Dependent claims set wt/wt % buckets:

Salt (species)	wt/wt % ranges explicitly recited
Na.GHB	Claim 3: ~5–40 (piecewise ranges); Claim 7 repeats discrete points (5,10,15,20,25,30,35,40)
K.GHB	Claim 4: ~10–40 (piecewise ranges); Claim 8 repeats discrete points (10–40)
Mg.(GHB)2	Claim 5: ~5–30 (piecewise ranges); Claim 9 repeats discrete points (5,10,15,20,25,30)
Ca.(GHB)2	Claim 6: ~20–80 (piecewise ranges); Claim 10 repeats discrete points (20–80)

Ratio examples for four-salt mixture

Claim 12: 8%:32%:20%:40% (Na:K:Mg:Ca)
Claim 13: 29%:31%:13%:27% (Na:K:Mg:Ca)
Claim 14: 8%:23%:21%:48% (Na:K:Mg:Ca)

B. Three-salt mixture (Na, K, Ca only)

Claim 15: mixture comprises Na.GHB, K.GHB, Ca.(GHB)2
Claim 16: wt/wt ranges:
- Na.GHB: ~5–40
- K.GHB: ~10–40
- Ca.(GHB)2: ~20–80
Claim 17: ratio example: 11%:39%:50% (Na:K:Ca)

C. Three-salt mixture (K, Mg, Ca only)

Claim 18: mixture comprises K.GHB, Mg.(GHB)2, Ca.(GHB)2
Claim 19: wt/wt ranges:
- K.GHB: ~10–50
- Mg.(GHB)2: ~20–60
- Ca.(GHB)2: ~10–40
Claim 20: ratio example: 33%:42%:25% (K:Mg:Ca)

How do the pH, concentration, oral liquid, and preservative-free limitations narrow enforceable scope?

A. Concentration window: 250–750 mg/mL vs narrower 300–750 and 400–600

Claim 21: 250–750 mg/mL (aqueous solution of the salt mixture)
Claim 30: 300–750 mg/mL
Claim 31: 400–600 mg/mL

A product at (for example) 200 mg/mL may avoid claims 21/30, leaving only claim 1 type coverage (if other limitations are not required).

B. pH window and stability/microbial resistance

Claim 21: pH 7.0–9.0
Claim 22: pH 7.3–8.5
Claims 21 and 27 both require:
- chemically stable
- resistant to microbial growth
- preservative-free

These are formulation-function limitations. In litigation, they frequently become evidence-heavy issues: stability testing and microbial challenge data can be used to show whether the accused formulation meets the functional criteria, beyond just salt wt/wt percentages.

C. Preservative-free creates a clean factual gate

Claim 21 and claim 28 explicitly recite “free of preservatives.”
Claim 32 allows optional excipients and lists antibacterial/antifungal agent categories, but that does not automatically negate “free of preservatives” unless the accused “antibacterial/antifungal agent” is categorized as a preservative in the regulatory/manufacturing sense and the claim construction follows that distinction.

D. Optional buffering acids

Claim 23: includes pH adjusting/buffering agent
Claim 24: acid
Claim 25: acid selection list
Claim 26: malic acid

If the accused product uses malic acid as the buffering acid and lands in the claimed salt mixture and pH bands, the dependent claims strengthen.

Where does the claim “molecular weight per oxybate equivalent equals sodium oxybate” land in infringement analysis?

Claim 33 requires:

“molecular weight per oxybate equivalent of the mixture of GHB salts is about the same as a formulation of sodium oxybate.”

This is a metric-based equivalence requirement. It ties salt composition to an oxybate-equivalency concept, which can be used to rebut design-around arguments that change the salt species but preserve “oxybate equivalent” delivered.

For an accused liquid, the analysis will typically map:

total oxybate equivalent delivered per mL/dose
conversion from salt mass to GHB oxybate equivalent
comparison to sodium oxybate’s equivalence scheme

If a competitor’s formulation matches sodium oxybate equivalents while using a different salt mixture, claim 33 becomes a potential bridge to composition coverage.

How does US 8,901,173 compare with common GHB/sodium oxybate patent themes?

US oxybate landscape typically clusters into:

active ingredient forms (salts, solvates)
liquid formulation stability (pH, concentration, preservative system)
dosage delivery and patient-use parameters
manufacturing/process claims
method-of-use claims (narcolepsy/cataplexy indications)

US 8,901,173 is concentrated in (1) and (2):

It is explicitly about the salt mixture of GHB with enumerated salts.
It is framed as a stable, microbial-resistant, preservative-free aqueous solution.
It does not read like a method-of-use or a device/dosing regimen claim.

That positioning matters for business strategy:

a generic or reformulation entrant can often be blocked if it must keep the same salt mixture and liquid constraints for stability without preservatives.
at the same time, if entrants can change salt species, pH, or preservative strategy, they may design around composition claims but still face method-of-use and regulatory exclusivity constraints from other patents not covered by 8,901,173.

What is the US patent landscape around US 8,901,173: likely related patent families and enforcement targets?

The prompt provides only the claim set, not bibliographic data, assignee, filing date, or priority. Without those, the only safe landscape conclusions are structural: what kinds of other US patents commonly co-exist in oxybate ecosystems and which are likely to overlap operationally with this particular salt-mixture approach.

Likely adjacent US patent claim categories in the same commercial zone

GHB salt forms and oxybate equivalents
- patents claiming sodium/potassium/magnesium/calcium salt compositions and conversion to GHB equivalents
Liquid oxybate formulation stability
- pH ranges, concentration ranges, chelators, tonicity agents, and microbial resistance strategies
Preservative systems and preservative-free claims
- claims about avoiding benzyl alcohol, parabens, or other preservatives and still maintaining microbial stability
Buffering agents
- citric/malic/phosphoric acid selection for stability windows
Manufacturing and sterilization approaches
- process patents for making salt mixtures or filling steps preserving stability
Dose form equivalence and oral solutions
- concentration and dosing unit conversion to oxybate equivalents

How 8,901,173 fits: the “design-around” map

A party seeking to avoid 8,901,173 would typically explore:

remove one required salt species (e.g., use only Na/K/Ca or only K/Mg/Ca, but still the claim 15 or claim 18 subsets could catch it if ratios land in range)
alter salt wt/wt % out of the explicit windows and avoid all listed ratio examples
alter total concentration outside 250–750 mg/mL (or outside 300–750 or 400–600 for dependent claims)
alter pH outside 7.0–9.0, or outside 7.3–8.5
use preservatives (break the “preservative-free” limitation) or use a system classified as a preservative
change buffering acid away from listed acids and away from malic acid where it is used

These are not legal guarantees, but they map directly to claim elements.

What litigation and exclusivity questions does this claim raise for generic and reformulation entrants?

Because 8,901,173 is a composition patent with narrow elements, the biggest risk for entrants is that their formulation must remain close to a stability-optimized oxybate liquid. If the market’s workable solutions converge on pH ~7–8.5 and preservative-free stability, the salt-mixture solution can become hard to move away from.

Paragraph IV / generics: composition patent exposure depends on Orange Book listings

Whether US 8,901,173 is asserted in Orange Book listing(s) (and for which drug product) cannot be determined from the prompt. Without that listing, the procedural posture (Paragraph IV, section viii statement, litigation posture) cannot be stated accurately.

What can be stated from the claim text:

If an accused generic is a liquid preservative-free aqueous oxybate with overlapping pH and concentration ranges, the practical claim match is high.
If the accused generic switches to a preserved formulation or a different pH/concentration regime, it may fall outside dependent claims 21/27/28 and claim 21’s functional stability constraints.

Biosimilar risk

This is not a biologic claim. Biosimilar frameworks do not apply.

Claim-by-claim scope summary (what an accused formulation must have to infringe)

Claim	What must be present	Main “gotcha” for enforcement
1	composition of GHB with 3+ salts from Na, K, Mg, Ca GHB salt list	number of salt species and allowed salt types
2	all four salts (Na, K, Mg, Ca)	must include Mg.(GHB)2 and Ca.(GHB)2 plus Na & K
3–6	wt/wt ranges for each salt species	measured wt/wt of each species
7–10	discrete wt/wt points	exact/near-exact compositional match
11	broader coupled ranges per salt	simultaneous compliance across all salts
12–14	specific wt/wt ratios	ratio matching and measurement method
15–17	subset Na/K/Ca only	avoid meeting all wt/wt ranges in subset
18–20	subset K/Mg/Ca only	avoid meeting all wt/wt ranges in subset
21	aqueous solution 250–750 mg/mL, pH 7.0–9.0, stable, microbial resistant, preservative-free	preservative-free + pH + concentration + functional stability
22	pH 7.3–8.5	pH boundary avoidance
23–26	buffering/pH adjusting agent is acid from list; malic acid option	formulation ingredient selection
27–29	liquid formulation; stable microbial resistance; preservative-free; suitable for oral	preservative-free + oral liquid category
30–31	GHB concentration 300–750; or 400–600 mg/mL	concentrate outside window
32	optional excipients incl. carrier, pH mediator, solvents, sweeteners, etc.	not usually a design-around basis because it is permissive
33	MW per oxybate equivalent about same as sodium oxybate	requires equivalence metric alignment

Key Takeaways

US 8,901,173 is a formulation-composition patent focused on a GHB salt mixture using Na.GHB, K.GHB, Mg.(GHB)2, and Ca.(GHB)2 with strict compositional and condition limitations.
The strongest infringement path is a product that is a preservative-free aqueous oral liquid in the claimed concentration (250–750 mg/mL; or 300–750 and 400–600 for dependents), at pH 7.0–9.0 (or 7.3–8.5), with measured salt wt/wt falling within the specified ranges/ratios.
Design-around levers are directly claim-linked: remove one required salt species, move salt wt/wt ratios outside the cited windows, shift pH outside the bands, change concentration outside the cited windows, or use preservatives such that “preservative-free” is not met.
The claim set includes an equivalence constraint vs sodium oxybate that can reduce the effectiveness of pure salt-substitution strategies if oxybate equivalent delivery remains aligned.

FAQs

Which salt types are required by US 8,901,173 for infringement?

At least three salts must be present, and each must be one of Na.GHB, K.GHB, Mg.(GHB)2, or Ca.(GHB)2. The full four-salt set is required for claim 2.

Does US 8,901,173 cover preservative-containing liquid oxybate formulations?

Claims 21 and 27–28 require the composition is free of preservatives. A preserved formulation is a direct risk-off lever against those dependent claims.

What pH range is covered by claim 21?

Claim 21 covers pH about 7.0 to about 9.0.

What concentration ranges are covered for the aqueous oral solution?

Claim 21 covers about 250 mg/mL to about 750 mg/mL. Dependent claims add narrower windows of 300–750 mg/mL and 400–600 mg/mL.

Is US 8,901,173 a method-of-use patent or a formulation patent?

Based on the provided claims, it is a formulation/composition patent focused on salt mixtures, pH, concentration, and preservative-free stability, not method-of-use.

References

US Patent 8,901,173 (provided claims text in prompt).

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Jazz	XYWAV	calcium oxybate; magnesium oxybate; potassium oxybate; sodium oxybate	SOLUTION;ORAL	212690-001	Jul 21, 2020		RX	Yes	Yes	8,901,173	⤷ 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	2013359114	⤷ Start Trial
Brazil	112015014007	⤷ Start Trial
Canada	2894876	⤷ Start Trial
China	105025892	⤷ Start Trial
Cyprus	1119918	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,901,173

Which drugs does patent 8,901,173 protect, and when does it expire?

Summary for Patent: 8,901,173