United States Patent 6,268,489: Scope, Claims, and US Patent Landscape for Crystalline Azithromycin Dihydrate
What does US 6,268,489 claim in plain scope terms?
US 6,268,489 is centered on crystalline azithromycin dihydrate and processes that crystallize azithromycin into that dihydrate form from THF plus an aliphatic hydrocarbon using at least 2 molar equivalents of water.
Claim set (as provided)
Claim 1
- Crystalline azithromycin dihydrate (composition claim).
Claim 2
- Method of preparing crystalline azithromycin dihydrate by crystallizing amorphous azithromycin or azithromycin monohydrate from a mixture of:
- tetrahydrofuran (THF), and
- a (C5-C7) aliphatic hydrocarbon,
- in the presence of at least 2 molar equivalents of water.
Claim 3
- Claim 2 where the hydrocarbon is hexane.
What is the legal and technical scope of each claim?
H2: Claim 1 scope - crystalline azithromycin dihydrate
Claim 1 covers the product, not a process. Its practical boundaries are dictated by how “crystalline azithromycin dihydrate” is construed in enforcement:
- It is limited to azithromycin in dihydrate form and crystalline material (not an amorphous dihydrate, not a non-dihydrate salt, not the monohydrate, not an anhydrous polymorph).
- The claim text you provided does not include functional limitations (no particle size, no DSC profile, no XRD peaks listed here), so scope is controlled by form identification in claim construction and infringement testing.
Business implication: Claim 1 is potentially broad against any manufacturer selling or using the specific crystalline dihydrate even if they use a different solvent system, as long as the delivered solid is the claimed form.
H2: Claim 2 scope - process crystallization using THF + C5-C7 hydrocarbon + water
Claim 2 is a narrower process claim with several hard constraints.
Required process elements
- Starting material:
- amorphous azithromycin OR azithromycin monohydrate
- Crystallization medium:
- tetrahydrofuran (THF)
-
- (C5-C7) aliphatic hydrocarbon
- Water requirement:
- at least 2 molar equivalents of water
- Outcome:
- crystalline azithromycin dihydrate
Interpretation pressure points
- Water equivalency: “at least 2 molar equivalents” is likely construed as a stoichiometric relationship based on azithromycin (or the relevant charged amount in the mixture), which can drive disputes around how water is measured (added water vs. water content in solvents and hydrate sources).
- Solvent system: The mixture must include THF and a C5-C7 aliphatic hydrocarbon. If a process replaces THF or uses a different hydrocarbon range (C4, C8+), it does not literally meet the element as written.
- Starting form: Claim 2 is limited to crystallization from amorphous azithromycin or the monohydrate, not from other azithromycin polymorphs or pre-formed dihydrate.
Business implication: Claim 2 has clear “design-around” levers (solvent identity, hydrocarbon carbon range, and water level).
H2: Claim 3 scope - hexane embodiment
Claim 3 narrows Claim 2 to:
Business implication: Claim 3 is the most enforceable target for labs and process developers using hexane; it also provides a clear fallback position in claim charts.
How does the claim architecture affect enforcement and freedom-to-operate?
US 6,268,489 uses both:
- a product form claim (Claim 1) and
- process form claims (Claims 2 and 3).
That combination changes exposure:
Infringement surfaces
| Exposure path |
What triggers it |
Most likely defensive approach |
| Product infringement (Claim 1) |
Sale or use of crystalline azithromycin dihydrate |
Prove different polymorph or non-dihydrate solid, or non-crystalline form |
| Process infringement (Claim 2) |
Use of THF + C5-C7 aliphatic hydrocarbon + ≥2 equiv water to crystallize from amorphous or monohydrate into the dihydrate |
Change solvent system, hydrocarbon carbon range, or water equivalency; or start from a different precursor form |
| Process infringement (Claim 3) |
Same as Claim 2 but with hexane |
Switch hydrocarbon (e.g., heptane vs hexane) or change other elements |
What is the practical formulation of “process constraints” implied by Claim 2?
From the claim text, the critical independent variables are:
- Solvent identity
- Co-solvent carbon range
- C5-C7 aliphatic hydrocarbon is mandatory.
- Water loading
- water must be present at ≥2 molar equivalents.
- Precursor solid
- crystallization must start from amorphous azithromycin or azithromycin monohydrate.
- Target solid
- outcome must be crystalline dihydrate.
A crystallization recipe that deviates on any one of these elements can avoid literal infringement of the corresponding method claims.
What does this imply for the patent landscape (US) around azithromycin forms?
H2: How form patents typically cluster around azithromycin dihydrate
In azithromycin solid-state chemistry, the landscape is commonly built around:
- polymorphs (crystalline forms),
- hydrates (monohydrate/dihydrate),
- solvent-mediated crystallizations,
- and conversion pathways between amorphous and hydrate forms.
In that context, US 6,268,489 sits squarely in the “hydrate form by crystallization from THF + hydrocarbon with controlled water” cluster because:
- it explicitly locks a solvent pair (THF + C5-C7 hydrocarbon),
- a water equivalence threshold, and
- a starting solid condition (amorphous or monohydrate).
H2: Where this patent is most likely to overlap other US filings
Even without pulling the full prosecution history or related family members, the overlap risk concentrates in the following US claim patterns:
- Crystallization of azithromycin dihydrate from mixed solvent systems using THF.
- Hydrate control methods that specify water equivalents or water content.
- Embodiments specifying hexane as co-solvent.
- Claims that relate to transforming amorphous azithromycin or monohydrate into dihydrate by adding controlled water in a defined solvent mixture.
Scope map: which activities are most likely covered?
H2: Likely covered activities
| Activity |
Coverage likelihood under provided claims |
| Selling isolating crystalline azithromycin dihydrate |
High for Claim 1 if product matches form |
| Manufacturing dihydrate via crystallization using THF + hexane + water ≥2 equiv |
High for Claims 2 and 3 |
| Converting monohydrate or amorphous to dihydrate using THF + C5-C7 hydrocarbon + water ≥2 equiv |
High for Claim 2 |
| Producing dihydrate using THF but co-solvent outside C5-C7 |
Not literal for Claim 2 |
| Producing dihydrate using a C5-C7 hydrocarbon but without THF |
Not literal for Claim 2 |
| Producing dihydrate with insufficient water (<2 equiv) |
Not literal for Claim 2 |
What design-arounds are structurally suggested by the claim language?
H2: Solvent and water design-around levers
| Claim element |
Design-around direction |
Impact |
| THF required (Claim 2) |
Replace THF with another primary solvent |
Breaks literal solvent element |
| Co-solvent range C5-C7 (Claim 2) |
Use C4 or C8+ aliphatic hydrocarbon |
Breaks literal carbon-range element |
| Water ≥2 molar equivalents (Claim 2) |
Reduce water to <2 equiv or use water-binding strategy |
Breaks water-equivalency element |
| Starting from amorphous or monohydrate (Claim 2) |
Start from another solid form not covered |
Breaks precursor limitation |
| Hexane specific (Claim 3) |
Use heptane or pentane instead |
Avoids Claim 3 literal embodiment |
Key patent landscape takeaways for US 6,268,489 (actionable)
H2: Risk drivers and due diligence priorities
- Product-form risk (Claim 1): if the final API solid is crystalline azithromycin dihydrate, it becomes the enforcement focal point regardless of upstream processing.
- Process risk (Claims 2-3): if internal or supplier crystallization steps match the solvent system and water loading, method claims create exposure even if the end-user is only repackaging or downstream processing.
- Most sensitive technical point: the water equivalency threshold and the use of THF with C5-C7 hydrocarbon.
Key Takeaways
- US 6,268,489 claims crystalline azithromycin dihydrate (Claim 1) and its crystallization from amorphous azithromycin or the monohydrate using a THF + (C5-C7 aliphatic hydrocarbon) solvent system with ≥2 molar equivalents of water (Claims 2-3).
- Claim 2 has multiple hard constraints that create clear literal design-around paths: remove THF, change hydrocarbon carbon range, drop water below 2 equivalents, or use a different precursor form.
- Claim 3 locks the process embodiment to hexane, making hexane-based THF crystallizations with controlled water the most direct match for method infringement risk.
- Landscape overlap risk is concentrated in US filings that also claim hydrate formation of azithromycin dihydrate via THF-mediated crystallization with controlled water.
FAQs
H2: What is the main difference between Claim 1 and Claims 2?
Claim 1 covers the crystalline azithromycin dihydrate product. Claim 2 covers a specific crystallization method (THF + C5-C7 hydrocarbon + ≥2 molar equivalents water, starting from amorphous or monohydrate).
H2: Does Claim 2 require hexane?
No. Claim 2 requires a (C5-C7) aliphatic hydrocarbon. Hexane is specifically required only in Claim 3.
H2: What is the most limiting parameter in Claim 2?
The water requirement: the method must use at least 2 molar equivalents of water.
H2: Can a process that uses THF but no C5-C7 hydrocarbon avoid Claim 2?
Yes, it does not satisfy the “THF and a (C5-C7) aliphatic hydrocarbon” element as written.
H2: If a supplier delivers crystalline azithromycin dihydrate made by a different method, is it still covered?
Claim 1 can still apply if the delivered solid is crystalline azithromycin dihydrate, since Claim 1 is a product/form claim.
References
- US Patent No. 6,268,489 (claims provided by user).
