Scope and claims of US Patent 5,763,493 and how the estate blocks generic bupropion hydrochloride stability risk

US 5,763,493 is a formulation-and-process patent that targets a narrow but commercially meaningful liability: degradation of bupropion hydrochloride in a solid dosage form under accelerated heat and humidity. The independent claim 1 ties (i) specific stabilizers, (ii) a stabilizer aqueous-solution pH window at a defined concentration (about 6% w/w), and (iii) performance thresholds after storage (undegraded bupropion hydrochloride % after 6 weeks at 40°C/75% RH). Dependent claims then narrow the pH and percent undegraded thresholds, and specify stabilizer levels and tablet/capsule bupropion strengths.

The enforcement leverage sits in claim preconditions: if a generic competitor cannot show the same stabilizer system with the same pH-in-solution profile and it fails the same stability outcome, it either avoids the claim scope by designing around or absorbs Paragraph IV litigation exposure if the product is evaluated as practicing the claimed stability-performance parameters.

What is US 5,763,493 (bupropion hydrochloride stabilizer pH and undegraded threshold patent) and what does it claim?

Fast answer: US 5,763,493 claims a solid pharmaceutical composition (and a method) that stabilizes bupropion hydrochloride using one of seven listed stabilizers, with a defined aqueous-solution pH range (about 0.9 to about 4 for a ~6% w/w solution), and requiring specific performance results after accelerated storage (at least about 80% w/w undegraded bupropion hydrochloride after 6 weeks at 40°C and 75% RH). Claim 12 adds a method of mixing the bupropion hydrochloride with that stabilizer system.

Claim 1 (independent) scope decomposition

Exerted elements (all must be met for literal infringement):

Dosage form/physical state: “pharmaceutical composition in solid form”
API and baseline identity: bupropion hydrochloride
Stabilizer selection: one stabilizer from:
- L-cysteine hydrochloride
- glycine hydrochloride
- malic acid
- sodium metabisulfite
- citric acid
- tartaric acid
- L-cystine dihydrochloride
Stabilizer function: present in “effective stabilising amount”
Stabilizer solution definition and pH constraint:
- “aqueous solution of the stabiliser in a concentration of about 6% w/w has a pH of about 0.9 to about 4”
Stability performance requirement after storage:
- composition contains at least about 80% w/w undegraded bupropion hydrochloride after 6 weeks at about 40°C and 75% relative humidity

Claim 12 (method) scope decomposition

Claim 12 is a corresponding method claim. It requires:

mixing bupropion hydrochloride with a stabilizer,
where the stabilizer’s ~6% w/w aqueous solution has pH about 0.9 to about 4,
to achieve the same stability performance outcome (at least about 80% w/w undegraded bupropion hydrochloride after 6 weeks at 40°C/75% RH).

Business implication: The method claim is potentially actionable even when a product is sold without proving how it was made, because practicing “mixing” steps can be established through formulation/CMC disclosures and manufacturing practices in discovery. The claim is anchored to a performance outcome, giving room to argue that the manufacturing process yields the claimed stability result even if vendors describe different blending sequences.

How broad are the pH and stabilizer definitions in claim 1, and what does “about 6% w/w aqueous solution pH 0.9 to 4” practically cover?

Fast answer: Claim 1 converts stabilizer chemistry into a measurable parameter. A competitor must show that, for the chosen stabilizer system at a ~6% w/w concentration in water, the pH falls outside roughly 0.9 to 4 to avoid the claim. If the selected stabilizer is within the listed group, then pH-at-6%-in-water becomes the main design-around lever.

Stabilizer list constrains substitution options

The stabilizer must be selected from the seven named compounds. That list is the primary narrowing factor. If a generic uses an alternative stabilizer (different chemical identity), it does not meet this element.

pH window is broad enough to complicate design-arounds

Claim 1 requires:

pH about 0.9 to about 4 for a ~6% w/w aqueous solution.

Dependent claims narrow the window further (claims 2 and 3). Dependent claims are important because they expand possible infringement theories: if the accused stabilizer system is within the narrower pH range, the patentee has more claim targets.

Dependent pH narrowing: claims 2 and 3

Claim 2: pH about 0.9 to 2
Claim 3: pH about around 1

Risk read-across: A stabilizer that is strongly acidifying (like certain acid salts/acids) may naturally land in the lower pH band. If marketed generics rely on pH adjustment using one of the listed acids or acid salts, they may fall into claim 2 or 3.

What stability performance thresholds does US 5,763,493 require, and how many outcomes trigger additional dependent claims?

Fast answer: The patent uses accelerated storage performance thresholds as claim-defining outcome metrics. At least three dependent claim tiers increase evidentiary and infringement coverage: 90%, 95%, and 98% undegraded after 6 weeks at 40°C/75% RH.

Performance tiers (after 6 weeks at 40°C / 75% RH)

Claim 1 baseline: at least about 80% w/w undegraded
Claim 4: at least about 90% w/w
Claim 5: at least about 95% w/w
Claim 6: at least about 98% w/w

Business implication for generics: If a competitor’s stability data shows only 80–89%, they still risk claim 1. If their stability data is higher, they risk additional dependent claims. From a litigation standpoint, the higher the product’s realized stability, the broader the patentee’s infringement map.

How “undegraded bupropion hydrochloride” becomes a testable endpoint

The claims hinge on the percent undegraded bupropion hydrochloride after defined storage conditions. This invites litigation over:

analytical method equivalence (how “undegraded” is quantified),
sampling and storage control,
what degradation products are counted or excluded.

Those disputes typically arise during expert discovery; the claim language itself already anchors the endpoint and the test conditions.

What stabilizer loading ranges are claimed, and where are the hard numerical boundaries?

Fast answer: Claims 7 and 8 impose stabilizer amount ranges “as a percent of the weight of bupropion hydrochloride in the composition.” Those numeric bands provide both infringement hooks and formulation design space.

Stabilizer loading ranges

Claim 7: stabilizer amount is 2.7% to 27% of the weight of bupropion hydrochloride
Claim 8: stabilizer amount is 5% to 16.2% of the weight of bupropion hydrochloride

Element specificity: The “% of bupropion hydrochloride weight” formulation metric is distinct from “% of total composition weight.” A competitor can reduce risk by calculating and controlling the amount relative to bupropion hydrochloride.

Interaction with “effective stabilising amount”

Claim 1 allows “effective” amounts. Claims 7 and 8 then lock ranges in dependent claims. In practice:

A generic could attempt to formulate outside the range in claims 7/8 while still meeting claim 1’s “effective” requirement, but that only avoids dependent claim coverage. It does not avoid claim 1 unless the product also fails claim 1’s performance or pH constraints.

Do the tablet/capsule dosage strength claims create separate patent coverage?

Fast answer: Yes. Claims 9–11 add dosage strength-specific product coverage for tablets/capsules containing the claimed stabilized composition.

Dosage strength windows (tablet/capsule)

Claim 9: bupropion hydrochloride 25 to 500 mg
Claim 10: bupropion hydrochloride 25 to 300 mg
Claim 11: bupropion hydrochloride is 50, 75, 100, or 150 mg

Coverage effect: If a product’s strength falls in any listed range, it may be within additional claim scope even if formulation parameters are otherwise met. Strength claims also matter in Orange Book and litigation because they align with specific listed presentations.

How does the method claim (claim 12) expand enforcement beyond the finished dosage form?

Fast answer: Claim 12 covers the act of mixing bupropion hydrochloride with a stabilizer meeting the defined ~6% aqueous-solution pH and producing the same accelerated stability result. That can broaden discovery and licensing leverage.

Key method elements

“mixing bupropion hydrochloride with a stabiliser”
stabilizer’s ~6% aqueous-solution pH about 0.9 to about 4
outcome: at least about 80% w/w undegraded after 6 weeks at 40°C / 75% RH

Practical consequence: Even if a competitor claims a different final formulation route, the method claim’s outcome requirement can still be argued to be practiced if the process yields the stability endpoint.

How many distinct claim “design-around” levers exist?

Fast answer: Four main levers: (1) stabilizer identity (must be one of seven), (2) stabilizer solution pH at ~6% w/w, (3) stability outcome after the accelerated test, and (4) stabilizer loading ranges (for dependent claims).

Design-around map tied to claim elements

Claim element	Literal avoidance approach	Litigation risk if partially avoided
Stabilizer identity	Use a non-listed stabilizer	Still may infringe if patentee argues equivalents for non-identity, but literal scope is narrower
Stabilizer solution pH	Choose a listed stabilizer but adjust grade/processing so pH-at-6% falls outside 0.9–4	pH is measured and can be contested; outcome stability may still keep claim 1 in play if pH is within range
Stability outcome	Formulate to reduce stability to below claimed threshold	If stability exceeds threshold, infringement risk increases across dependent claims
Stabilizer loading	Formulate outside 2.7–27% and/or 5–16.2% bands	Avoid dependent claims 7/8 but claim 1 may remain if “effective stabilizing amount” and performance are met

What is the patent landscape impact of this claim structure for bupropion hydrochloride generics in the US?

Fast answer: US 5,763,493 is a formulation-stability patent that can complicate generic product shelf-life equivalence arguments and can be enforced against specific bupropion hydrochloride presentations whose CMC stability data meets the claimed thresholds.

Where it fits in a typical generic strategy

ANDA formulation matching: A filer aims for bioequivalence, not necessarily for the identical stability approach. This patent requires matching stability performance under defined stress conditions using listed stabilizers with defined pH.
Stability package alignment: If the chosen stabilizer system naturally improves stability to high undegraded percentages, it raises the chance of meeting dependent tiers (claim 4–6).
Presentation mapping: Tablet/capsule strengths in claims 9–11 create additional targeting opportunities.

Litigation posture the claims incentivize

If an accused generic uses one of the listed stabilizers and achieves high stability, the patentee has multiple claim hooks (1 plus 4/5/6; 9–11 if strength overlaps).
If the accused generic avoids the pH window or fails the undegraded threshold, it can attempt to defeat literal infringement, but it then becomes an evidentiary fight over how “about” and measurement are applied.

Which companies are likely exposed, and how do you assess exposure by presentation and stability?

Fast answer: Without Orange Book ties and specific ANDA product presentations, the exposure universe cannot be enumerated from the claim text alone. What can be extracted from the patent language is an exposure scoring framework: match bupropion HCl strength, then compare stabilizer chemistry and the defined pH-at-6%-in-water, then validate the accelerated stability endpoint.

Exposure scoring framework using claim-mandated variables

Strength overlap with claims 9–11
- Is the sold/ANDA strength within 25–500 mg, 25–300 mg, or {50, 75, 100, 150} mg?
Stabilizer identity
- Is the stabilizer one of the seven listed chemicals (no substitutes)?
Stabilizer solution pH
- Does a ~6% w/w aqueous solution of the stabilizer land in:
  - 0.9–4 (claim 1), and potentially
  - 0.9–2 (claim 2), or
  - ~1 (claim 3)?
Stability outcome
- Does the product show ≥80%, ≥90%, ≥95%, or ≥98% undegraded after 6 weeks at 40°C/75% RH?

Outcome-driven risk: A product meeting ≥98% undegraded is maximally exposed because it satisfies claim 1 and all dependent performance tiers (claims 4–6). A product meeting only ≥80% is still within claim 1 but not claims 4–6.

How strong is the patent estate for formulation stability, based on the internal claim architecture alone?

Fast answer: Strength is high on enforceability focus (clear numerical endpoints and constrained stabilizer list) and moderate on potential workarounds (because generics can attempt to move outside stabilizer identity, outside the pH window, or fail the undegraded thresholds). The claim is structured to support both product and method theories.

Strength indicators in the claim text

Defined test conditions: 40°C/75% RH, 6 weeks.
Defined endpoint: % w/w undegraded bupropion HCl.
Defined stabilizer set: seven named chemicals.
Defined pH measurement context: pH of a ~6% w/w aqueous solution.

Potential weakening factors embedded in the language

“about” qualifiers on pH and thresholds can broaden interpretation and create expert dispute.
Outcome-based claims still depend on analytical and storage control, which can be contested.

Key claim chart: US 5,763,493 elements vs. generic design and litigation relevance

Area	Claim requirement	What a generic must prove to avoid	What the patentee uses to prove infringement
Composition	Solid composition	Not needed if other elements missing	Product formulation and composition characterization
Stabilizer identity	One of seven listed stabilizers	Use non-listed stabilizer	CMC, excipient list, supplier specs
pH constraint	pH of ~6% aqueous solution is ~0.9–4	Demonstrate pH outside range	Stabilizer-grade testing and pH measurement
Stability endpoint	≥80% undegraded after 6 weeks at 40°C/75% RH	Show <80% undegraded under same conditions and method	Stability protocol adherence and results
Higher thresholds	≥90% / ≥95% / ≥98% undegraded	Show performance below thresholds	Accelerated stability data showing tier compliance
Loading	2.7–27% or 5–16.2% (dependent)	Use outside ranges	Weight % excipient calculations and lot data
Strength	Tablet/capsule bupropion strength ranges (dependent)	Sell strengths outside ranges	Label claims and Orange Book presentation

Key Takeaways

US 5,763,493 is a stability-focused bupropion hydrochloride solid formulation and mixing method patent anchored to (i) a closed list of stabilizers and (ii) a defined pH measurement protocol plus (iii) a defined accelerated stability performance endpoint.
Claim 1 requires the stabilizer’s ~6% w/w aqueous solution pH to be about 0.9–4 and the product to achieve at least about 80% w/w undegraded bupropion HCl after 6 weeks at 40°C/75% RH.
Dependent claims escalate coverage through pH narrowing (claims 2–3), higher undegraded tiers (claims 4–6), stabilizer loading bands (claims 7–8), and dosage strength ranges (claims 9–11).
For infringement or design-around planning, the highest-leverage variables are stabilizer identity (must be one of seven), stabilizer pH at ~6% in water, and the accelerated stability test outcome.

FAQs

1) What data matters most to assess infringement risk under US 5,763,493?
Accelerated stability results (6 weeks at 40°C/75% RH) showing the percent undegraded bupropion HCl, plus the stabilizer identity and the stabilizer’s ~6% w/w aqueous-solution pH.

2) Can a generic avoid the patent by using a different stabilizer than the seven listed compounds?
Using a non-listed stabilizer avoids the stabilizer identity element needed for claims 1 and 12, but actual risk depends on whether the formulation is assessed under literal claim language.

3) If a generic’s product is more stable than the patent requires, does that increase risk?
Yes. If stability exceeds the claimed thresholds (≥90%, ≥95%, ≥98% undegraded), it potentially satisfies multiple dependent claims.

4) How do “about” ranges affect design-around planning?
“About” widens the practical interpretation of pH and stability thresholds, which increases the need to treat borderline pH and endpoint values as litigation-sensitive.

5) Do the dosage strength claims mean the same formulation could avoid infringement by changing strength?
Strength-only avoidance may reduce exposure to dependent claims 9–11 if the strength falls outside their ranges, but claim 1 and claim 12 coverage can still remain if the composition meets their core elements.

References

US Patent 5,763,493. (text provided in user prompt; claims quoted).

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9315856	Jul 30, 1993

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	232383	⤷ Start Trial
Australia	698883	⤷ Start Trial
Australia	7235294	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,763,493

Summary for Patent: 5,763,493