United States Patent 5,900,424: Omeprazole Magnesium Scope, Claims, Expiration and Patent Landscape

U.S. Patent No. 5,900,424 protects a defined crystalline form of omeprazole magnesium and processes for making it. The core product claim requires crystallinity above 70% by X-ray powder diffraction. Dependent claims add particle size, density, water content, residual solvent, and hygroscopicity limits. Separate claims cover manufacture, purification, drying, and therapeutic use.

The patent is no longer an active exclusion right. Its commercial importance is historical and analytical: it established a quality and manufacturing specification for omeprazole magnesium associated with delayed-release omeprazole products. Current generic or branded-product risk depends primarily on later formulation, coating, regulatory, and manufacturing patents.

What does U.S. Patent 5,900,424 protect?

The patent protects two related subject matter groups:

A crystalline omeprazole magnesium material with specified physical and chemical properties.
Processes for manufacturing that material by reacting omeprazole or an omeprazole salt with a magnesium alcoholate, removing inorganic salts, crystallizing with water, and isolating the crystals.

The principal claim is Claim 1:

“An omeprazole magnesium salt having a degree of crystallinity which is higher than 70% as determined by x-ray powder diffraction.”

This is a product claim defined by measurable characteristics rather than by a chemical formula alone. Omeprazole magnesium that falls within the claimed physical-property profile could potentially implicate Claim 1 regardless of whether it was made by the patented process.

The patent also includes method-of-use claims for inhibiting gastric acid secretion and treating gastric-acid-related diseases.

What are the independent claims in Patent 5,900,424?

Claim	Category	Scope
1	Product	Omeprazole magnesium with crystallinity above 70%
11	Manufacturing process	Reaction with magnesium alcoholate, inorganic-salt separation, water crystallization and isolation
20	Improved manufacturing process	Separation of inorganic salts before crystallization by water addition
21	Treatment method	Administration for inhibiting gastric acid secretion
22	Treatment method	Administration for gastric-acid-related diseases

Claims 2 through 10 narrow Claim 1 by adding product specifications. Claims 12 through 19 narrow or elaborate Claim 11. Claims 21 and 22 incorporate selected product claims, but not every dependent claim.

How broad is the crystalline omeprazole magnesium product claim?

Claim 1 is materially broader than the dependent product claims because it requires only crystallinity above 70%. It does not expressly require:

A particle diameter below 30 micrometers;
A density between 1.33 and 1.35 g/cm³;
Water content between 5% and 10%;
Methanol or other solvent below a specified threshold;
Hygroscopicity below a specified level.

A product meeting the crystallinity threshold but failing the particle-size or density limitations could still fall within Claim 1 if the crystallinity measurement is valid and reproducible.

Claim 1 is not unlimited. The accused material must be:

Omeprazole magnesium;
A salt rather than unneutralized omeprazole;
More than 70% crystalline under the patent’s X-ray powder diffraction methodology.

The phrase “degree of crystallinity” creates an evidentiary issue. In a dispute, the parties would likely contest the reference standard, sample preparation, instrument settings, peak integration, amorphous baseline, and reproducibility of the X-ray method. A result close to 70% would carry greater litigation risk than a result materially below or above the threshold.

What additional product properties are covered by Claims 2 through 10?

Claim	Limitation
2	Crystallinity above 75%
3	Mean particle diameter below 30 µm, preferably below 20 µm
4	Density from 1.33 to 1.35 g/cm³
5	Water content from 5% to 10% by weight
6	Solvent content below 0.1% by weight
7	Solvent content below 0.05% by weight
8	Claims 6 or 7 where the solvent is an aqueous alcohol
9	Claims 6 or 7 where the solvent is methanol
10	Hygroscopicity below 2% weight increase after one month at up to 94% relative humidity

Claim 2 is a straightforward crystallinity refinement. Claim 3 addresses particle engineering, which can affect dissolution, suspension behavior, content uniformity, processing, and dosage-form performance.

Claim 4 covers a narrow density range. Because density measurements can vary with powder packing and instrument conditions, the powder-pycnometer methodology is important. Claim 5 covers a relatively high water-content range, consistent with a hydrated or water-associated crystalline material rather than a fully anhydrous solid.

Claims 6 through 9 target residual solvents. Claim 7 is narrower than Claim 6. Claim 9 is narrower than Claim 8 because it specifies methanol. Claim 10 addresses storage stability and moisture uptake.

The claims do not expressly require that all listed properties be present simultaneously. Each dependent claim narrows the claim from which it depends. A product may infringe Claim 1 without meeting Claims 3, 4, 5, 6, 7, 8, 9, or 10.

What manufacturing processes are protected?

Claims 11 through 20 protect a crystallization process built around magnesium alcoholate chemistry.

The principal process sequence is:

Treat omeprazole or an omeprazole salt with magnesium alcoholate in solution.
Separate inorganic salts from the reaction mixture.
Crystallize magnesium omeprazole by adding water.
Isolate the crystalline product.

Claim 11 requires the sequence in “consecutive steps.” That sequencing language may limit the claim if a process performs the operations in a materially different order.

Claim 12 specifies magnesium methyl alcoholate. Claim 13 specifies methanol as the solvent. Claims 14 and 15 cover alternative isolation methods:

Centrifugal separation of crystals; or
Crystallization followed by filtration.

Claims 16 through 19 address post-crystallization operations:

Purification and drying;
Washing with a solution of polar solvents;
Drying under reduced pressure;
Heating to evaporate remaining solvent.

These process claims are narrower than the product claim because they require performance of each specified operation. A manufacturer can avoid literal infringement of Claim 11 if it produces omeprazole magnesium through a materially different route, such as a different magnesium reagent, a different solvent system, or a crystallization sequence that does not separate inorganic salts before water-induced crystallization.

What does Claim 20 add to the patent?

Claim 20 is an improvement claim. It addresses a process for making crystalline magnesium omeprazole in which inorganic salts are separated from the reaction mixture before the crystallization step.

Its practical purpose is process control. Removing inorganic salts before crystallization can improve:

Crystal purity;
Crystallinity;
Residual-solvent performance;
Filtration or centrifugation;
Batch consistency;
Physical stability.

Claim 20 does not require every limitation of Claim 11 in the same form. It recites a process for manufacturing a crystalline magnesium salt and identifies the improved operation as separating inorganic salts before crystallization by adding water. Its interpretation would depend on the exact prosecution history and claim construction.

What do the method-of-use claims cover?

Claim 21 covers administering a therapeutically effective dose of magnesium omeprazole falling within selected product claims to inhibit gastric acid secretion.

Claim 22 covers administering the specified magnesium omeprazole for gastric-acid-related diseases.

The claims are limited by both:

The identity and physical characteristics of the magnesium omeprazole; and
The therapeutic purpose.

They do not expressly cover every proton-pump-inhibitor use. They are directed to gastric acid inhibition and gastric-acid-related disease treatment.

The method claims are less commercially significant after patent expiration. Before expiration, they could have created a separate infringement theory against a marketed product or labeled use, although enforcement would require proof concerning the claimed product characteristics and the accused indication.

When did Patent 5,900,424 lose exclusivity?

U.S. Patent No. 5,900,424 issued on May 4, 1999. Its term was governed by the 20-year patent-term framework applicable to the relevant filing or international filing date, subject to any patent-term adjustment or terminal disclaimer recorded by the USPTO.[1]

The patent is expired and cannot currently block manufacture, sale, or use of omeprazole magnesium on the basis of its original patent claims. Patent expiration does not invalidate the technical disclosure. It ends the enforceable exclusion right.

The expiration analysis should be separated from regulatory exclusivity:

Right	Status
Patent 5,900,424	Expired
Crystalline omeprazole magnesium claims	Public-domain subject matter, subject to later patents
Process claims	Expired
Method-of-use claims	Expired
FDA approval exclusivity	Separate NDA-specific inquiry
Later formulation patents	Must be assessed independently
Trade secrets and know-how	May remain relevant after patent expiration

What is the Orange Book status of Patent 5,900,424?

The Orange Book listing question is product-specific. A patent is not “Orange Book protected” in the abstract. FDA listing depends on whether the patent was submitted for a specific approved drug application and whether FDA accepted it for publication under the statutory listing categories.[2]

Patent 5,900,424 has been associated with the omeprazole magnesium product and formulation patent landscape, including products using omeprazole magnesium as the active ingredient. A current Orange Book assessment must distinguish:

The original prescription Prilosec products;
Omeprazole magnesium delayed-release products;
Over-the-counter omeprazole products;
Later abbreviated new drug applications;
Patents listed against the active ingredient, formulation, method of use, or drug-delivery system.

The patent’s expiration means it does not create a current Orange Book blocking right even if it was historically listed. A current Paragraph IV analysis must review the FDA’s active listing data and any later patents associated with the relevant NDA.[2]

Were Paragraph IV challenges or generic litigation tied to this patent?

A Paragraph IV certification is made against an Orange Book-listed patent in an ANDA. The applicant asserts that the patent is invalid, unenforceable, or will not be infringed.[3]

Because Patent 5,900,424 is expired, it is no longer a practical basis for a new Paragraph IV dispute. Historical ANDA litigation may have involved this patent or related omeprazole formulation patents, but the commercially material question today is whether later, unexpired patents cover:

Delayed-release pellets;
Enteric coatings;
Specific excipient systems;
Capsule or tablet architecture;
Dosing regimens;
OTC labeling;
Manufacturing processes;
Alternative salt or polymorph forms.

The patent itself should not be treated as a current litigation barrier merely because it appears in historical patent records.

How strong was the patent estate for omeprazole magnesium?

Patent 5,900,424 was strongest against manufacturers that used the claimed crystalline material and the specified manufacturing route. Its strength came from the combination of:

A broad crystalline-product claim;
Objective analytical thresholds;
A process claim focused on salt removal and water crystallization;
Narrower claims covering commercially relevant material properties.

Its weaknesses included:

Dependence on analytical measurement;
Potential variability in crystallinity testing;
A narrow process sequence;
The ability to design around the magnesium alcoholate route;
Limited relevance after expiration;
The possibility that a later product could use a different solid form or formulation architecture.

The patent was stronger as a quality- and manufacturing-specification patent than as a comprehensive drug-product patent. It did not, by itself, protect every omeprazole dosage form, every enteric coating, or every commercial formulation containing omeprazole magnesium.

What generic entry risks exist for omeprazole magnesium?

After expiration, the main risks shift from this patent to later rights and regulatory requirements.

Risk area	Relevance
Active pharmaceutical ingredient	Low risk from Patent 5,900,424
Crystalline form	Low risk from this expired patent; later polymorph patents require review
Manufacturing route	Low risk from this expired patent
Enteric coating	Potentially material under later formulation patents
Delayed-release pellets	Potentially material
Capsule or tablet composition	Product-specific
Labeling and indication	Method-of-use patent dependent
FDA bioequivalence	Commercial and regulatory risk
CMC reproducibility	Material because the product has dissolution and stability specifications
Residual solvent and moisture control	Important for approval, but not independently blocking after expiration

A generic applicant that uses omeprazole magnesium should still characterize crystallinity, water, solvent, density, particle size, and hygroscopicity. Those tests may support CMC control even though the patent claims are expired.

How does Patent 5,900,424 compare with formulation patents?

Patent 5,900,424 focuses primarily on the active pharmaceutical ingredient and its manufacture. Formulation patents generally focus on the finished dosage form.

Patent type	Typical protected subject matter	Relevance to 5,900,424
Solid-form patent	Crystallinity, polymorph, hydrate, salt	Directly aligned
API process patent	Reaction, purification, crystallization	Directly aligned
Pellet patent	Inert core, drug layer, enteric coat	Separate
Enteric-coating patent	Polymer, plasticizer, coating sequence	Separate
Dosage-form patent	Capsule, tablet, suspension	Separate
Method patent	Disease, dose, administration schedule	Partly aligned
Manufacturing trade secret	Operating parameters and scale-up	Separate from patent term

A complete freedom-to-operate review must therefore examine the entire product architecture, not only the active ingredient patent.

What geographic coverage did the patent have?

U.S. Patent 5,900,424 provided rights only in the United States. Related patent families may have covered Europe, Canada, Japan, Australia, and other jurisdictions, but each national patent required a separate term, prosecution history, and legal-status review.

The U.S. expiration did not automatically terminate foreign counterparts. Conversely, expiration or lapse of a foreign counterpart did not affect U.S. rights. International coverage should be mapped by:

Priority application;
PCT publication;
National-phase filings;
Granted patent number;
Expiration date;
Supplementary protection certificate or patent-term extension;
Abandonment, lapse, or annuity status.

What manufacturing barriers remain after patent expiration?

Patent expiration removes the principal legal barrier created by this patent. Manufacturing barriers can remain in practice:

Reproducible crystallization at commercial scale;
Control of particle-size distribution;
Removal of inorganic salts;
Low residual methanol or aqueous-alcohol content;
Moisture control;
Stability under high humidity;
Consistent delayed-release dissolution;
Regulatory comparability;
Validated analytical methods.

These are technical and regulatory barriers, not continuing rights under Patent 5,900,424. Process know-how that was not disclosed in the patent may remain protected as a trade secret if it was kept confidential and meets applicable trade-secret requirements.

Key Takeaways

Patent 5,900,424 covers crystalline omeprazole magnesium, beginning with a crystallinity threshold above 70%.
The dependent product claims add limits for crystallinity, particle size, density, water, residual solvent, and hygroscopicity.
Claims 11 through 20 cover magnesium-alcoholate manufacturing, inorganic-salt separation, water crystallization, isolation, purification, and drying.
Claims 21 and 22 cover therapeutic administration for acid inhibition and gastric-acid-related diseases.
The patent is expired and is not a current blocking right.
Historical Orange Book relevance does not create current enforceability after expiration.
Current generic-entry risk is more likely to arise from later delayed-release, enteric-coating, dosage-form, method-of-use, or manufacturing patents.
Product-by-property enforcement would depend heavily on validated X-ray diffraction, particle-size, density, moisture, solvent, and hygroscopicity measurements.
The patent was technically important for crystalline API quality and manufacturing but did not comprehensively protect every omeprazole magnesium formulation.

FAQs

Is omeprazole magnesium protected by Patent 5,900,424 today?

No. The patent has expired. Later patents covering a particular formulation, coating, polymorph, use, or manufacturing process may still require separate analysis.

Does every omeprazole magnesium product infringe Claim 1?

No. Claim 1 requires omeprazole magnesium with crystallinity above 70% as determined by X-ray powder diffraction. The chemical identity alone is insufficient.

Can a manufacturer avoid the process claims by using a different magnesium reagent?

Potentially. Claims 11 through 20 require specified operations, including magnesium alcoholate treatment and inorganic-salt separation before crystallization. A materially different process may avoid literal infringement, subject to claim construction and equivalents analysis.

Are the water-content and residual-solvent limits mandatory for all claims?

No. They appear in dependent claims. A product may fall within Claim 1 without meeting Claims 5 through 9.

Does patent expiration eliminate FDA approval requirements for omeprazole magnesium?

No. Expiration removes the patent exclusion right. FDA approval, bioequivalence, chemistry-manufacturing-controls, stability, labeling, and applicable Orange Book requirements remain separate regulatory obligations.

References

United States Patent and Trademark Office. (1999). U.S. Patent No. 5,900,424, crystalline form of omeprazole magnesium.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
United States Code. (2023). 21 U.S.C. § 355(j): Abbreviated applications and patent certifications.
United States Code. (2023). 35 U.S.C. § 154: Contents and term of patent; provisional rights.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Sweden	9302396	Jul 09, 1993

PCT Information
PCT Filed	July 08, 1994	PCT Application Number:	PCT/SE94/00680
PCT Publication Date:	January 19, 1995	PCT Publication Number:	WO95/01977

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	212628	⤷ Start Trial
Australia	679766	⤷ Start Trial
Australia	7198194	⤷ Start Trial
Brazil	9406940	⤷ Start Trial
Canada	2166794	⤷ Start Trial
China	1064680	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,900,424

Summary for Patent: 5,900,424