United States Drug Patent 6,589,959: Scope, Claims, Expiration, Litigation, and Rosuvastatin Patent Landscape

U.S. Patent No. 6,589,959 protects a specific hydrated crystalline form of rosuvastatin calcium, the active pharmaceutical ingredient in Crestor. Its principal claim is a solid-state, polymorph claim defined by an X-ray powder diffraction pattern. The patent does not broadly cover rosuvastatin, rosuvastatin calcium in every physical form, or all pharmaceutical uses.

The patent was granted to AstraZeneca and expired in 2021. It no longer creates a U.S. patent barrier to generic rosuvastatin calcium. Its historical importance was greater than its current blocking value because generic applicants could challenge whether their proposed product contained the claimed crystalline form.

What compound does U.S. Patent 6,589,959 protect?

The patent covers a hydrated crystalline calcium salt of rosuvastatin. The chemical entity is:

Rosuvastatin calcium
Also known as the calcium salt of rosuvastatin
A synthetic HMG-CoA reductase inhibitor
The active ingredient in Crestor
Used primarily to reduce LDL cholesterol and cardiovascular risk

The claim identifies the compound structurally as:

“bis[(E)-7-4-(4-fluorophenyl)-6-isopropyl-2-[methyl(methylsulfonyl)amino]pyrimidin-5-yl-3,5-dihydroxyhept-6-enoic acid]calcium salt.”

The patent is directed to the physical form of that compound rather than to the underlying pharmacological activity. U.S. Patent No. 6,589,959 is titled “Crystalline form of rosuvastatin calcium salt.” [1]

What are the claims of U.S. Patent 6,589,959?

The patent contains two claims.

Claim	Subject matter	Claim type
1	Hydrated crystalline rosuvastatin calcium having specified XRPD peaks	Product-by-characterization
2	Pharmaceutical composition containing the crystalline form and a pharmaceutically acceptable carrier	Composition

What does claim 1 require?

Claim 1 requires all of the following:

Rosuvastatin calcium.
A crystalline form.
Hydration.
The claimed XRPD peak profile.
Peaks at approximately:
- 4.92° 2θ
- 6.93° 2θ
- 9.35° 2θ
- 11.50° 2θ
- 18.76° 2θ
- 23.12° 2θ

The claim is therefore narrower than a claim to rosuvastatin calcium generally. A material that contains rosuvastatin calcium but lacks the claimed crystalline and hydrated characteristics would fall outside the literal scope of claim 1.

What does claim 2 require?

Claim 2 covers a pharmaceutical composition containing the crystalline material of claim 1 and a pharmaceutically acceptable carrier.

Typical carriers may include excipients used in oral tablets, such as fillers, binders, disintegrants, lubricants, coatings, and stabilizers. Claim 2 does not independently protect every rosuvastatin tablet. It requires the composition to contain the particular crystalline form covered by claim 1.

How does the XRPD limitation affect infringement?

The XRPD limitation is the central scope restriction.

An accused product generally would be evaluated by:

Powder X-ray diffraction
Hydration-state testing
Solid-state characterization
Moisture and water-content analysis
Comparison against the claimed peak positions
Assessment of peak intensity, relative position, and analytical variability

The claim does not state that the six peaks are the only peaks present. In pharmaceutical solid-state claims, a list of characteristic peaks ordinarily identifies a crystalline form through its diffraction signature. The complete pattern, sample preparation, instrument conditions, and accepted peak-position tolerance can affect the infringement analysis.

A generic manufacturer could avoid literal infringement if its process produces:

An amorphous form
A different rosuvastatin calcium polymorph
An anhydrous form
A hydrate with a materially different diffraction pattern
A different salt or free-acid form
A product in which the claimed form is absent or not present in the relevant drug substance

The presence of the same crystalline form in a finished tablet would create a different analysis from the presence of a different form in the active pharmaceutical ingredient. Claim 2 reaches a composition containing the claimed form, but it does not impose a particular tablet strength, dosage regimen, excipient system, or therapeutic indication.

What does U.S. Patent 6,589,959 not cover?

The patent does not, based on the quoted claims, cover the following subject matter independently:

Subject matter	Covered by the quoted claims?
Rosuvastatin free acid	No
All rosuvastatin calcium forms	No
Amorphous rosuvastatin calcium	No
Every rosuvastatin calcium hydrate	No
A different crystalline polymorph	No
Rosuvastatin manufacturing processes	No
Treatment of hypercholesterolemia	No
Cardiovascular-risk reduction methods	No
Specific tablet strengths	No
Specific excipient combinations	No
Combination therapy with other drugs	No
Pharmaceutical composition containing the claimed form	Yes, through claim 2

The patent is consequently a formulation and solid-state patent, not a broad active-ingredient, treatment-method, or manufacturing patent.

When did U.S. Patent 6,589,959 expire?

The patent was granted on July 8, 2003. Its 20-year U.S. patent term ran from the relevant nonprovisional filing date and expired in 2021. The principal term is generally reported as May 18, 2021. [1]

Event	Date
U.S. filing	May 18, 2001
Patent grant	July 8, 2003
Expected patent expiration	May 18, 2021
Current status	Expired
Current blocking value	None in the United States

The patent’s expiration removed the direct patent restriction associated with the claimed crystalline form. Any pediatric exclusivity associated with an FDA product could have extended regulatory protection for a limited period, but it would not revive the expired patent or create a new patent right.

What was the Orange Book status of rosuvastatin calcium?

FDA’s Orange Book historically listed patents associated with Crestor and rosuvastatin calcium products. Orange Book listings can include patents covering:

The active ingredient
A salt or chemical form
A formulation
A method of use
Other patent rights submitted by the NDA holder

U.S. Patent No. 6,589,959 was relevant to the historical Crestor patent estate because it covered the crystalline rosuvastatin calcium form used in commercial drug products. The listing did not mean that every generic rosuvastatin calcium product necessarily infringed the patent. In an ANDA case, the applicant’s formulation, drug-substance form, certifications, and proposed labeling would control the analysis. [2]

After expiration, the patent no longer supports a current Paragraph IV enforcement action in the ordinary sense. Historical Orange Book presence remains relevant to understanding the timing of generic entry and earlier litigation.

Which companies challenged the Crestor patent estate?

AstraZeneca faced generic challenges to the Crestor patent estate from multiple generic manufacturers, including Apotex and other major ANDA applicants. The most significant reported appellate litigation involving AstraZeneca’s rosuvastatin patents included AstraZeneca LP v. Apotex, Inc., 633 F.3d 1042 (Fed. Cir. 2010). [3]

The litigation concerned AstraZeneca patents covering rosuvastatin calcium and related subject matter. The case illustrates the principal generic strategy:

File an ANDA with a Paragraph IV certification.
Assert that the relevant patent is invalid, unenforceable, or not infringed.
Force an infringement action under the Hatch-Waxman framework.
Seek approval or launch rights based on litigation results or settlement terms.

The precise scope of each case depended on the patents asserted and the generic applicant’s proposed product. A Paragraph IV challenge to a formulation or crystalline-form patent does not necessarily challenge the entire rosuvastatin patent estate.

How strong was the patent estate for rosuvastatin?

The estate was layered rather than dependent on one patent.

Core compound protection

The earlier rosuvastatin compound patents protected the active molecule and related chemical subject matter. Those rights were more important to the initial market exclusivity period but expired before or around the period when generic rosuvastatin became commercially available.

Salt and product-form protection

Rosuvastatin calcium patents protected the commercially selected salt and related product characteristics. These patents could create a more direct barrier to a generic product using rosuvastatin calcium.

Crystalline-form protection

U.S. Patent No. 6,589,959 occupied this category. Its value depended on whether the commercial drug substance used the claimed hydrate and whether a generic applicant could use another form without losing product performance, stability, manufacturability, or regulatory comparability.

Process protection

Separate patents and applications relating to rosuvastatin manufacturing could create process risks even after a product patent expired. Process patents generally require proof that the accused manufacturer uses the claimed process. They do not automatically block a product made by a non-infringing route.

Regulatory exclusivity

FDA exclusivity associated with the original NDA operated separately from the patent term. Crestor received FDA approval in 2003 under NDA 21-366. [4] Regulatory exclusivity delayed certain generic approvals during the early commercial period, but it did not extend the life of U.S. Patent No. 6,589,959.

What generic entry risks existed for rosuvastatin?

Before expiration, the main risks were:

A Paragraph IV challenge based on noninfringement
Invalidity arguments directed to obviousness or claim construction
Use of a different polymorph or anhydrous form
Use of an amorphous drug substance
A product-by-process distinction
A formulation designed to avoid claim 2
Litigation settlements allowing an agreed launch date
Regulatory approval after expiration of the listed patents

After expiration, the patent-specific risk was substantially reduced. Commercial barriers shifted toward:

API manufacturing scale
Bioequivalence
FDA approval timing
Supply agreements
Pricing
Distribution access
Manufacturing know-how
Other unexpired patents, if any
Market concentration among generic suppliers

For a current generic entrant, U.S. Patent No. 6,589,959 is primarily a historical freedom-to-operate issue. It is not a live patent obstacle.

Did the patent create biosimilar risk?

No. Rosuvastatin is a chemically synthesized small molecule, not a biologic. The relevant FDA pathway is an abbreviated new drug application, not a biosimilar application under the Public Health Service Act.

The appropriate competitive products are generic rosuvastatin calcium products. Biosimilar concepts such as reference-product exclusivity, interchangeability, and patent dance procedures do not apply to this product.

What manufacturing and intellectual-property barriers remain?

The patent’s expiry does not eliminate all technical barriers. A generic manufacturer still must control:

Polymorph selection
Hydration state
Particle-size distribution
Crystallization conditions
Impurity profile
Residual solvents
Stability under storage
Tablet dissolution
Bioequivalence
Batch-to-batch solid-state consistency

The claimed XRPD form may remain commercially useful even without patent protection because it can provide reproducible processing and stability characteristics. That is a manufacturing advantage, not an enforceable exclusion right.

A manufacturer using the same form after patent expiry does not face infringement liability under this patent. It may still need to protect its own process improvements, impurity-control methods, crystallization conditions, or formulation technology through separate patents or trade secrets.

How does this patent compare with broader rosuvastatin patents?

Patent category	Typical protection	Breadth relative to U.S. 6,589,959
Rosuvastatin compound patent	Active molecule and chemical analogs	Broader chemical scope
Rosuvastatin calcium patent	Calcium salt or pharmaceutical product	Broader salt/product scope
Crystalline-form patent	Specific hydrate or polymorph	Narrower, but potentially easier to test analytically
Formulation patent	Tablet composition or release profile	Narrower formulation scope
Method-of-use patent	Treatment of lipid disorders	Narrower use scope
Process patent	Manufacturing route or intermediate	Different infringement theory

U.S. Patent No. 6,589,959 was strongest when the commercial rosuvastatin calcium product used the claimed hydrate and when generic applicants had limited ability to qualify a different solid form. Its weakness was claim dependency on a readily testable physical characteristic. Once the patent expired, that limitation ceased to have exclusionary force.

Key Takeaways

U.S. Patent No. 6,589,959 covers a hydrated crystalline form of rosuvastatin calcium.
Claim 1 is defined by a six-peak XRPD profile at specified 2θ values.
Claim 2 covers pharmaceutical compositions containing that crystalline form.
The patent does not broadly cover rosuvastatin, all rosuvastatin calcium forms, methods of treatment, or manufacturing processes.
The patent expired in 2021, with the principal expiration date reported as May 18, 2021.
It is no longer a live U.S. patent barrier to generic rosuvastatin calcium.
Historical litigation included AstraZeneca’s enforcement activity against generic applicants, including Apotex.
The patent was part of a layered Crestor estate that included compound, salt, formulation, method, and process rights.
Rosuvastatin is a small molecule, so generic competition proceeds through ANDAs rather than biosimilar applications.
Current commercial barriers are primarily regulatory, manufacturing, quality, supply, and pricing barriers.

FAQs About U.S. Patent 6,589,959

Does U.S. Patent 6,589,959 cover Crestor itself?

It covered the hydrated crystalline rosuvastatin calcium form used in the commercial product, not every possible rosuvastatin formulation or physical form.

Can a generic manufacturer use the same rosuvastatin calcium crystal form now?

Yes, the patent expired in 2021. Other patents, regulatory requirements, or contractual restrictions must be analyzed separately.

Is claim 1 a polymorph claim?

Yes. It is a crystalline-form claim defined by hydration and an XRPD diffraction pattern.

Does claim 2 protect a particular Crestor tablet formulation?

No. Claim 2 broadly requires a pharmaceutical composition containing the claimed crystalline form and a pharmaceutically acceptable carrier. It does not recite a specific excipient combination or dosage strength.

Was a Paragraph IV certification relevant to this patent?

Yes. Before expiration, an ANDA applicant could use a Paragraph IV certification to challenge validity or infringement of an Orange Book-listed patent, potentially triggering Hatch-Waxman litigation.

References

United States Patent and Trademark Office. (2003). U.S. Patent No. 6,589,959: Crystalline form of rosuvastatin calcium salt.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, Orange Book.
AstraZeneca LP v. Apotex, Inc., 633 F.3d 1042 (Fed. Cir. 2010).
U.S. Food and Drug Administration. (2003). Crestor prescribing information, NDA 21-366.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9900339	Jan 09, 1999

PCT Information
PCT Filed	December 23, 1999	PCT Application Number:	PCT/GB99/04439
PCT Publication Date:	July 20, 2000	PCT Publication Number:	WO00/42024

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	282027	⤷ Start Trial
Australia	1882600	⤷ Start Trial
Australia	762909	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,589,959

Summary for Patent: 6,589,959