US Patent 4,861,786 Landscape for Torasemide Injection: Claim Scope, Patent Estate, and Generic Entry Risks
Executive summary
US Patent 4,861,786 covers an alkaline, sterile, vein-compatible torasemide injection composition (and a kit and a preparation method) defined primarily by: (i) torasemide concentration ranges, (ii) buffer pH 9.3–9.9 with limited buffer capacity, (iii) an organic solvent system at 5–20 wt% that is substantially aldehyde/ketone-free with specified aldehyde ppm limits, and (iv) oxygen-free storage or presence of a reducing agent. Downstream enforcement and generic-competition risk hinges on whether an ANDA-type product can match the exact solvent quality constraints, alkaline buffer window, and oxidation-protection requirement while remaining “vein-compatible” and sterile.
The analysis below dissects claim scope by element, maps typical design-around pathways, and outlines the US patent landscape implications for torasemide injection formulations.
What is US Patent 4,861,786 and what product does it claim to protect?
US 4,861,786 is directed to an injectable torasemide composition in aqueous sterile alkaline solution intended for intravenous use (“vein-compatible”) with anti-inflammatory or diuretic activity. The independent claim is structured around a specific physicochemical formulation architecture: pH, buffering strength, solvent identity and amount, aldehyde ppm constraints, and oxidation-control conditions.
Independent claim 1: protected composition “architecture”
Claim 1 requires all of the following (in combination):
- Sterile aqueous alkaline solution for injection in mammals.
- Torasemide at 2–40 mg/mL (or physiologically acceptable salt).
- Physiologically compatible alkaline buffer with:
- pH 9.3–9.9
- buffer capacity up to 0.1 val/L
- Organic solvent that is substantially free of aldehyde or ketone, with:
- <30 ppm aldehyde
- present at 5–20 wt%
- selected from:
PEG (MW 100–1500), PPG (MW 150–1000), glycerol, propylene glycol, ethanol, propanol
- Composition storage conditions:
- stored in an oxygen-free atmosphere OR in the presence of a physiologically compatible reducing agent
Independent claim 1 also explicitly defines intended use functionally:
- “inhibition of inflammation or promotion of diuresis”.
Key dependent claims that narrow operative claim boundaries
- Claim 2: organic solvent is PEG (MW 200–600)
- Claim 3: organic solvent is PEG 400
- Claim 4: organic solvent at about 10 wt%
- Claim 5: torasemide concentration 0.01–0.2 mol/L
- Claim 6: torasemide particle size <10 µm
- Claim 7: “torasamide” particle size <2 µm
(note: the claim text appears to reference “torasamide”; if treated as a typo in prosecution history, scope would turn on intrinsic evidence)
- Claim 8: aldehyde in organic solvent <10 ppm
- Claim 9–13: buffer may be specific weak-acid salt or TRIS-type buffer, and optionally includes a further diuretic such as canrenoate and/or furosemide
- Claims 14–15: optional isotonicity maintenance agent (e.g., NaCl, fructose, lactose, glucose)
- Claim 16: optional adjuvants/additives (tenside, minerals, vitamins)
- Claim 17: kit for preparation containing the listed elements (torasemide, alkaline buffer components, solvent quality constraints, isotonicity agent, reducing agent)
- Claim 18: process steps for preparing the solution
- Claim 19: method of inhibiting inflammation and promoting diuresis via injection of the claim 1 solution
How broad is US 4,861,786 claim scope: what is required vs. what is permissive?
Claim 1 is broad on several axes but rigid on core limitations. The strategy for evaluating exclusivity or infringement risk is to separate mandatory limitations from optional/permissive ones.
Mandatory limitations (all must be met to fall within claim 1)
- Torasemide concentration 2–40 mg/mL
- Sterile injectable aqueous solution
- pH window 9.3–9.9
- Buffer capacity ≤0.1 val/L
- Organic solvent:
- selected from enumerated solvent categories
- at 5–20 wt%
- aldehyde ppm constraint (<30 ppm in claim 1)
- “substantially free” of aldehyde/ketone
- Oxygen-free storage or reducing agent presence
- The product is intended to be vein-compatible (how this is construed depends on specification/definitions in the patent record)
Permissive flexibility
- Torasemide salt form: “physiologically acceptable salt”
- Buffer components: claim 9 later specifies examples (phosphate, carbonate, glycinate, arginate, N-methyl glucosaminate, amino acids, TRIS), but claim 1 itself only requires physiologically compatible alkaline buffer at pH and capacity.
- Solvent choice within the enumerated group: PEG/PPG/glycerol/propylene glycol/alcohols.
- Optional add-ons: isotonicity agents, tensides, vitamins/minerals, additional diuretics, etc.
Practical implication for infringement and design-around
To avoid claim 1, a generic or branded competitor can focus on breaking at least one mandatory element:
- move pH outside 9.3–9.9
- use a buffering system that changes buffer capacity beyond 0.1 val/L
- change solvent type outside the enumerated list
- change solvent amount outside 5–20 wt%
- control aldehyde/ketone impurities differently (including exceeding the ppm threshold, while meeting safety)
- remove the oxygen-free/reducing agent feature
- remove “substantially free aldehyde/ketone” characteristics
What does the solvent “aldehyde ppm” requirement do to freedom-to-operate?
The solvent quality constraints are among the strongest discriminatory elements because they introduce a material-spec limitation that can be measured and litigated.
Claim 1 vs dependent claim 8: <30 ppm vs <10 ppm aldehyde
- Claim 1: solvent contains <30 ppm aldehyde
- Claim 8: solvent contains <10 ppm aldehyde
A competitor that satisfies claim 1’s <30 ppm could still avoid claim 8 if aldehyde remains between 10 and 30 ppm. Conversely, if a product is designed to be ultra-low aldehyde, it may inadvertently meet claim 8.
“Substantially free of aldehyde or ketone”
This phrase adds an additional boundary beyond aldehyde ppm, potentially implicating ketone impurity levels. If the specification gives definitions or test methods, those become central to claim construction.
Oxygen-free storage or reducing agent
This requirement turns formulation practice into an IP boundary:
- a product that omits reducing agents may still comply if its packaging and storage architecture is proven “oxygen-free.”
- a generic that uses reducing agents must ensure the reducing agent is “physiologically compatible” and present in the claimed manner.
How do pH and buffer capacity limit the formulation window?
Claim 1 has two orthogonal buffer constraints:
- pH 9.3–9.9
- buffer capacity up to 0.1 val/L
Most standard injectable buffers are designed around millimolar buffers with capacities tied to ionic strength and titration curves. The “buffer capacity” metric makes this claim more defensible: it restricts the formulation beyond just pH.
Dependent claim 9–10: buffer system examples
Claim 9 ties buffer candidates to specific classes:
- sodium/potassium/ammonium salts of weak acids
- TRIS (tris-(hydroxymethyl)-aminomethane)
- or a further physiologically active material acting as a buffer
Claim 10 provides weak acid examples:
- phosphate, carbonate
- glycinate, arginate
- N-methyl glucosaminate
- other amino acids
A competitor choosing a different weak acid system might still infringe claim 1 if it meets pH and capacity limits, even if it avoids the examples in claim 10.
What other claim elements can be used for design-around: concentration, particle size, isotonicity?
Torasemide concentration (claim 1 and claim 5)
- Claim 1: 2–40 mg/mL
- Claim 5: 0.01–0.2 mol/L
This can be leveraged if a competitor’s dose strength falls outside these ranges. Many commercial presentations may use fixed mg/mL strengths; if those strengths align with claim ranges, design-around requires changing the formulation concentration and possibly total volume.
Particle size (claims 6 and 7)
- Claim 6: torasemide particle size <10 µm
- Claim 7: “torasamide” particle size <2 µm
If the formulation uses a different particle size distribution, a generic could attempt to escape these dependents. But note that these are dependent claims: avoiding particle size does not avoid claim 1 unless the claim construction treats these features as required in the independent claim (it does not).
Isotonicity agent (claims 14–15)
These features are optional in dependent claims, so they do not expand the independent claim’s mandatory scope.
What does the kit claim (claim 17) cover and how does it affect generic manufacturing?
Claim 17 claims a “kit for the preparation of an injectable solution” with constituent components:
- torasemide
- alkaline buffer (weak acid salts and/or TRIS, pH 9.3–9.9)
- organic solvent with aldehyde ppm constraints (<30 ppm)
- isotonicity agent
- reducing agent
This is a manufacturing and distribution hook. Even if a generic firm does not sell a final injectable, selling a kit with the defined components can create exposure.
Process claim (claim 18): preparation steps and what changes matter
Claim 18 recites:
- suspending torasemide in the aldehyde/ketone-free organic solvent
- dissolving by adding aqueous alkali to reach pH 9.3–9.9 by acid or alkali addition
- filtering undissolved particles
- sterilizing
A design-around could attempt to change:
- solvent quality control methods
- dissolution order
- pH adjustment technique (while still producing a final product that might infringe claim 1 is the key issue)
- sterilization method if it affects “process of which comprises” structure (depending on whether claim is closed to only the listed steps)
Does claim 19 create separate method-of-use infringement risk?
Claim 19 covers injecting the claim 1 solution to inhibit inflammation or promote diuresis in mammals. Method-of-use claims can matter if:
- a product is used off-label but evidence supports the claimed intended use
- there is a dispute about “in mammals” or about the functional framing of anti-inflammatory effect
In practice, for a diuretic like torasemide, claims tied to “promotion of diuresis” may map closely to marketed indication labeling. Enforcement typically focuses on whether the administered product is the infringing formulation rather than on whether the clinician’s intent matches the claim language.
What does the “vein-compatible” language change in enforcement?
“Vein-compatible” is a formulation-performance descriptor. In litigation, it typically becomes a claim-construction question:
- whether it is limiting (often yes if it provides a functional requirement tied to the disclosed composition)
- whether it is supported by objective parameters (osmolarity, pH tolerance, irritation markers, stability)
If the specification defines vein compatibility thresholds or test methods, a generic may need to demonstrate it either does not meet those thresholds or that compatibility is inherent.
What patents likely co-exist in the torasemide injection formulation landscape around US 4,861,786?
Without a full Orange Book record, global family document list, and the prosecution history for 4,861,786, the only defensible statement is what this patent itself covers. Still, a business-grade landscape needs the following categories to assess risk around an injected diuretic:
Landscape categories you typically see alongside this type of formulation patent
- Torasemide API and salts (earlier composition-of-matter or crystalline form patents)
- Injectable solubilization systems
- PEG/PPG-alcohol-glycerol solvent systems
- aldehyde/ketone impurity control approaches
- Buffer systems and pH windows
- Storage stability and oxidation control
- oxygen-free packaging
- reducing agents
- Process claims
- order of mixing, pH adjustment, filtration/sterilization
- Therapeutic use claims
- inflammation inhibition claims vs diuresis framing
- Kits
- two-component or multi-component preparation
For risk modeling, US 4,861,786 functions as a formulation patent with measurable impurity and physicochemical limitations. That tends to block simple substitutions with different excipients if those substitutions keep the same pH and solvent identity/levels and maintain aldehyde/ketone profiles.
When does US 4,861,786 lose exclusivity? (Patent term framework)
No filing date, priority date, or terminal disclaimer details are provided in the prompt. Without that, a precise expiration date cannot be stated here.
What generic entry risks exist for torasemide injection if a product matches claim 1?
The infringement trigger is direct: if a generic’s product contains the same combination of:
- alkaline buffer at pH 9.3–9.9
- buffer capacity ≤0.1 val/L
- solvent at 5–20 wt% from the enumerated solvent group
- aldehyde impurity <30 ppm and “substantially aldehyde/ketone free”
- oxygen-free storage or reducing agent
then it is within the claim 1 formulation envelope.
Where a generic can be vulnerable even after “partial” differences
A generic may change torasemide particle size, isotonicity agents, or exact buffer salt choice and still infringe claim 1 if the core required elements remain intact.
Key takeaways
- US 4,861,786 is a formulation-centric patent for torasemide injection with hard limits on pH (9.3–9.9), buffer capacity (≤0.1 val/L), and organic solvent impurity quality (<30 ppm aldehyde) coupled to oxygen-free or reducing agent storage.
- The solvent system is enumerated and constrained by both identity (PEG/PPG/glycerol/propanediols/alcohols) and amount (5–20 wt%), making “minor” excipient swaps unlikely to avoid infringement if the replacement still meets the same enumerated category and weight range.
- Dependent claims narrow the envelope further with PEG molecular weight selections and tighter impurity (<10 ppm aldehyde) and particle size limits.
- The kit claim and process claim create additional infringement vectors beyond selling a ready-to-use injectable.
- Risk-focused design-around centers on violating at least one mandatory element: pH window, buffer capacity, solvent identity/amount, aldehyde/ketone impurity qualification, or oxygen-free/reducing-agent condition.
FAQs
1) What formulation changes most directly avoid claim 1?
Moving outside pH 9.3–9.9, exceeding buffer capacity 0.1 val/L, changing the solvent system outside the enumerated list or outside 5–20 wt%, using a solvent with aldehyde/ketone levels that do not meet the “substantially free” and <30 ppm aldehyde requirement, or eliminating the oxygen-free/reducing agent condition.
2) If a generic uses PEG 400, does it automatically infringe claims 2 or 3?
Not automatically. Claim 2 and claim 3 require additional conditions tied to PEG selection while claim 1 already requires the broader solvent framework and other formulation limitations.
3) Does avoiding the aldehyde impurity limit escape claim 1?
Yes, if the generic’s solvent does not satisfy the “substantially free of aldehyde or ketone” requirement or does not meet the <30 ppm aldehyde limitation of claim 1.
4) Can a product infringe via method-of-use even if it is not the same formulation?
Claim 19 is tied to “injecting the solution of claim 1.” If the administered product does not meet claim 1’s formulation limitations, claim 19 exposure is reduced.
5) What role does the buffer capacity limit play in non-pH design-around?
Buffer capacity is a distinct physicochemical limitation. A product can be at pH 9.3–9.9 yet still fall outside claim scope if buffer capacity is >0.1 val/L.
References
No patent bibliographic data (publication date, priority date, assignees, or family members) was provided beyond the claims text. Therefore, no external citations can be assembled from the prompt.
