United States Patent 4,639,458: Scope, Claim Coverage, and US Patent Landscape
What does US 4,639,458 claim cover?
US Drug Patent 4,639,458 claims a specific solid oral dosage composition of norfloxacin with tightly defined excipient ranges and a tablet format. The claim set is narrow in formulation scope and broad only to the extent it covers any tablet made from the claimed composition.
Claim-by-claim scope
| Claim |
Claim language (key elements) |
Core coverage |
Practical meaning for products |
| 1 |
Composition containing by weight: 80–85% norfloxacin, 13.5–18.5% microcrystalline cellulose, 0.5–2% magnesium stearate, 1–4.5% croscarmellose sodium |
Exact excipient classes + numeric ranges |
Covers tablets or compositions meeting all four wt% windows simultaneously |
| 2 |
Composition of claim 1 with trace amount of colorant |
Same formulation as claim 1 plus color |
Adds optional colorant; does not change the excipient ranges |
| 3 |
Tablet prepared from composition of claim 1 or 2 |
Dosage form made from the claimed formulation |
Covers the made tablet product where the starting composition meets claim 1/2 |
In-scope formulation features
Claim 1 requires, by weight:
- Norfloxacin: 80–85%
- Microcrystalline cellulose: 13.5–18.5%
- Magnesium stearate: 0.5–2%
- Croscarmellose sodium: 1–4.5%
Because all four ranges are express and cumulative, product infringement requires the accused formulation to land in every window at the same time.
Out-of-scope formulation paths
The numeric windows create clear design-around routes:
- Lower norfloxacin content below 80% or above 85%
- Microcrystalline cellulose below 13.5% or above 18.5%
- Magnesium stearate below 0.5% or above 2%
- Croscarmellose sodium below 1% or above 4.5%
- Substituting a different diluent/disintegrant system that removes either microcrystalline cellulose or croscarmellose sodium as the specified excipient types at the claimed levels
How broad are the claims in legal and commercial terms?
The patent’s coverage is limited to:
- A composition defined by wt% ranges of specific excipients, not a functional description.
- A tablet produced from that composition.
It does not claim:
- Any process parameters (e.g., wet granulation vs direct compression) in the provided claim text.
- Any alternative cellulose grade or substitute disintegrant.
- A broader norfloxacin tablet range (for example, 70–90% norfloxacin) or functional disintegrant limits.
Range-based interpretation implications
The claim uses “about” and explicit ranges. In enforcement, “about” can expand slightly beyond the stated endpoints depending on how the patent teaches the formulation and how courts treat measurement tolerances. Still, the claim is fundamentally range-limited and excipient-type specific.
Trace colorant does not expand excipient scope
Claim 2 is dependent on claim 1 and adds only:
It does not add new excipient classes or permit replacing croscarmellose sodium or microcrystalline cellulose.
Tablet claim tracks composition
Claim 3 covers tablets “prepared from” the claimed composition. In practice:
- If a competitor’s tablet composition does not satisfy claim 1/2 wt% windows, claim 3 is also avoided.
- If the tablet is made from a composition that meets claim 1/2, claim 3 creates a direct product capture route.
What is the patent landscape around US 4,639,458?
US 4,639,458 sits within a dense historical area of norfloxacin solid dosage formulations and generic-era formulation patenting. The key landscape issue is that, for older antibiotic products, many formulation patents exist but often focus on:
- solid forms
- disintegration properties
- specific excipient choices
- specific compression or manufacturing steps
However, the specific combination of microcrystalline cellulose and croscarmellose sodium at defined wt% windows with high norfloxacin loading (80–85%) is a narrower hook than many broad antibiotic formulation patents.
Landscape segmentation (business-relevant)
| Segment |
Typical claim strategy |
How it relates to 4,639,458 |
| Fixed excipient wt% ranges |
Claim specific wt% of API + excipients |
4,639,458 is in this bucket and is enforcement-sensitive to formulation testing |
| Functional disintegrant claims |
Claims based on “effective amount” or disintegration time |
Usually broader in practice, but may still require specific excipient identity |
| Solid form / polymorph claims |
Claim specific crystal forms, hydrates, etc. |
Different axis; could still block manufacturing if solid form differs |
| Process claims |
Claim granulation, drying, compression parameters |
Not evident in the claim text provided; may appear in related patents |
| Combination product claims |
Different therapeutic scope |
Not implicated by the provided claim text |
How do you map potential infringement risk for a norfloxacin tablet today?
A defensible risk mapping uses composition testing against claim 1’s wt% windows.
Direct infringement logic
For claim 1:
- Accused product must be a composition where:
- norfloxacin is 80–85% by weight
- microcrystalline cellulose is 13.5–18.5% by weight
- magnesium stearate is 0.5–2% by weight
- croscarmellose sodium is 1–4.5% by weight
For claim 2:
- Same as claim 1, plus a trace colorant. This likely does not change infringement if the base formulation is captured.
For claim 3:
- Tablet that is prepared from the claim 1/2 composition.
Most effective design-around levers
Since claim elements are all excipient identity plus wt%:
- Move norfloxacin outside 80–85%
- Move croscarmellose sodium outside 1–4.5%
- Replace microcrystalline cellulose with another diluent or remove it as the specified cellulose type
- Replace magnesium stearate with another lubricant system or move its level outside 0.5–2%
The highest-probability design-around in practice is changing API loading or the disintegrant level/type, because those usually drive formulation constraints such as tablet hardness, disintegration, and dissolution.
What does this imply for portfolio strategy and freedom-to-operate?
Given the narrowness of claim 1’s composition windows:
- A formulation variant that lands outside any one wt% band likely avoids literal infringement.
- A formulation that lands inside all four windows remains exposed for both composition and tablet claims.
Practical freedom-to-operate posture
For generic or authorized formulation entrants:
- Formulate and analytically verify a composition that deliberately misses at least one claim range or replaces an excipient type.
- Treat “about” as a litigation risk factor and build a formulation margin away from endpoints.
- Use comparator lot testing across the manufacturing scale, because blending and compression can shift actual wt% distribution.
For buyers/investors evaluating exclusivity value:
- This patent’s value is most meaningful if it blocks commercialization of a high-norfloxacin capsule-tablet architecture that otherwise would be hard to reformulate without impacting performance.
Key Takeaways
- US 4,639,458 claims a norfloxacin tablet formulation with fixed excipient identity and tight wt% ranges:
- 80–85% norfloxacin
- 13.5–18.5% microcrystalline cellulose
- 0.5–2% magnesium stearate
- 1–4.5% croscarmellose sodium
- Claim 2 only adds trace colorant and does not expand excipient substitution rights.
- Claim 3 captures tablets prepared from the claim 1/2 composition, so composition compliance is the infringement gate.
- The most direct design-arounds are moving any component outside its claimed wt% window or substituting excipient identity (especially the microcrystalline cellulose or croscarmellose sodium system).
FAQs
1) Does claim 3 cover any norfloxacin tablet?
No. Claim 3 covers a tablet “prepared from” the claimed composition in claim 1 or claim 2. If the tablet composition does not meet claim 1’s wt% windows, claim 3 does not attach.
2) Can a competitor add extra excipients beyond the listed ones?
The provided claim text requires the stated components “by weight” within the listed ranges; extra excipients are not expressly permitted or excluded in the claim excerpt. In enforcement, the accused product must still satisfy the wt% ranges for the specified components.
3) Is a different disintegrant a likely infringement risk?
A disintegrant substitution that removes croscarmellose sodium as the specified component at 1–4.5% by weight is the clearest path to avoid claim 1.
4) How does the “about” term affect the ranges?
“About” can create endpoint ambiguity depending on how courts interpret tolerance. From a risk perspective, formulations should be designed to sit comfortably away from endpoints, not just within the numeric bands.
5) What formulation lever most efficiently avoids claim 1?
The highest-leverage levers are typically:
- changing norfloxacin loading outside 80–85%, or
- changing croscarmellose sodium outside 1–4.5%.
Sources (APA):
[1] United States Patent No. 4,639,458.
