United States Patent 5,916,595: Claim Scope, Expiration, and Controlled-Release Statin Patent Landscape

U.S. Patent No. 5,916,595 covers a multilayer controlled-release tablet for statins and related alkyl esters of hydroxy-substituted naphthalene compounds. The broadest claim requires four technical elements: a compressed osmotic tablet core, a water-swellable polymer, an osmotic agent, and an outer coating combining a pH-sensitive polymer, a channeling agent, and a water-insoluble cellulosic polymer.

The patent issued on June 29, 1999. Based on its 1997 priority date, its nominal 20-year patent term ended in June 2017, subject to any patent-term adjustment. It no longer presents a current U.S. blocking patent for generic or reformulated statin products. The patent is directed to drug delivery architecture, not to the underlying statin molecules, which were already known compounds.

What does U.S. Patent 5,916,595 protect?

The patent protects a controlled-release dosage form using an osmotic and swelling mechanism combined with pH-responsive coating technology.[1]

The essential architecture is:

A compressed tablet core.
An alkyl ester of a hydroxy-substituted naphthalene compound.
A pharmaceutically acceptable water-swellable polymer.
An osmotic agent.
An outer coating completely covering the core.
A pH-sensitive coating agent.
A channeling agent.
A water-insoluble cellulosic polymer.
A specified polymer weight ratio of 0.1:1 to 0.75:1.
A combined coating weight of 0.5% to 5% by weight.

The claims focus on the interaction between the core and coating. A product containing lovastatin alone would not fall within claim 1. It would also need to include the specified controlled-release formulation structure.

What drug compounds are covered?

Claim 2 identifies four compounds:

Compound	Coverage under claim 2	U.S. commercial relevance
Mevastatin	Yes	Not broadly commercialized as a U.S. finished drug
Pravastatin	Yes	Pravachol and generic pravastatin
Simvastatin	Yes	Zocor and generic simvastatin
Lovastatin	Yes	Mevacor and generic lovastatin

The claims do not cover all statins. Atorvastatin, rosuvastatin, fluvastatin and pitavastatin are outside the express Markush group in claim 2. A product containing one of those molecules would not satisfy the compound limitation as written.

The phrase “alkyl ester of a hydroxy substituted naphthalene compound” is broader in claim 1 than the specific list in claim 2, but claim 1 still requires the compound to fit that chemical description and the dosage-form limitations.

How broad is independent claim 1?

Claim 1 is the principal broad claim. It covers a formulation rather than a method of treatment, manufacturing process or chemical compound.

Claim 1 limitation chart

Claim limitation	Scope and technical effect
Controlled-release formulation	Requires modified release rather than a conventional immediate-release tablet
Alkyl ester of hydroxy-substituted naphthalene compound	Defines the active pharmaceutical ingredient class
Compressed tablet core	Excludes capsules, multiparticulates and noncompressed dosage forms unless the accused product includes an equivalent claimed core
Water-swellable polymer	Supports hydration, swelling and controlled drug release
Osmotic agent	Creates osmotic driving force after water ingress
Outer coating completely covering the core	Requires a continuous external coating layer
pH-sensitive coating agent	Creates pH-dependent permeability or dissolution
Channeling agent	Produces channels or pores as the coating hydrates or dissolves
Water-insoluble cellulosic polymer	Provides structural control over the coating
Polymer ratio of 0.1:1 to 0.75:1	Creates a numerical composition limitation
Combined coating weight of 0.5% to 5%	Creates a second numerical limitation

The numerical limitations materially narrow the claim. A formulation with the same drug, polymer classes and release objective may avoid literal infringement if the relevant polymer ratio or total coating weight falls outside the claimed ranges.

The term “channeling agent” also creates a formulation-specific construction issue. The accused excipient must function as a channel-forming or pore-forming component, not merely be present as an inactive ingredient.

What dependent claims add to the patent scope?

Claims 3 through 10 narrow claim 2 by specifying additional ingredients or layers.

Claim	Added limitation
3	A first coating seals the tablet core
4	The core has an inner enteric coating
5	The dosage form has an enteric overcoat
6	The water-swellable polymer is polyethylene oxide
7	The osmotic agent is anhydrous lactose
8	The pH-sensitive agent is a methacrylic acid/methyl methacrylate copolymer
9	The core contains a surfactant
10	The surfactant is sodium lauryl sulfate

These claims create potential design-around routes. A competing product could use a different swellable polymer, osmotic agent, enteric system, surfactant or coating polymer. The limitations also allow an infringement analysis to distinguish between a product that has the general architecture of claim 1 and a product that includes the narrower lovastatin, polyethylene oxide, lactose or sodium lauryl sulfate combinations.

What does claim 11 specifically protect?

Claim 11 is a narrow combination claim directed to a lovastatin tablet. It requires:

Lovastatin in the compressed core;
A polyoxyethylene water-swellable polymer;
Anhydrous lactose; and
An outer coating containing a methacrylic acid/methyl methacrylate copolymer and a cellulose acetate polymer;
A coating-polymer weight ratio of 0.1:1 to 0.75:1.

Claim 11 is narrower than claim 1 because it identifies the active ingredient, core excipient classes and coating polymer classes. It may be easier to test analytically, but it also has more opportunities for a competing formulation to avoid literal infringement.

The references to polyoxyethylene and polyethylene oxide are technically related polymer descriptions, but claim construction would depend on the patent specification, prosecution history and the precise grade and molecular-weight characteristics used in the commercial product.

What does claim 12 protect?

Claim 12 covers a three-layer dosage form:

A compressed tablet core containing the active compound, swellable polymer and osmotic agent;
An inner coating containing a pH-sensitive coating agent; and
An outer coating containing a pH-sensitive agent, channeling agent and water-insoluble cellulosic polymer.

Claim 12 is important because it requires two coating layers with different structural functions. A formulation with only the claimed external coating may fall under claim 1 but not claim 12. Conversely, an inner enteric or pH-sensitive coating can create additional claim exposure if the external coating also meets the composition and ratio requirements.

When did U.S. Patent 5,916,595 lose exclusivity?

The patent’s nominal term ended in 2017, based on a 20-year term measured from its earliest effective nonprovisional filing date.[1][2]

Event	Date or status
Earliest priority period	1997, based on the patent record
U.S. patent issued	June 29, 1999
Nominal 20-year term	Ended in 2017
Current status	Expired by term
Current blocking effect	None for new U.S. launches

The exact terminal date depends on the recorded priority chain and any patent-term adjustment. Patent-term extension under 35 U.S.C. § 156 would generally be associated with regulatory review of an approved drug product. The patent’s formulation subject matter and the age of the covered statins do not indicate a current term-extension issue.

Expiration eliminates the enforceable exclusionary right. It does not erase the technical disclosure, claim history or potential relevance to validity, inventorship, prosecution or freedom-to-operate analyses involving related patents.

What is the Orange Book status of Patent 5,916,595?

The patent is not a current Orange Book barrier because its term has ended. Orange Book-listed patents are relevant to approved drug products only when they meet FDA listing requirements and remain legally operative.[3]

The patent record alone does not establish that U.S. Patent 5,916,595 was listed against a specific reference product. The patent covers a controlled-release formulation, while the major U.S. statin reference products were primarily associated with immediate-release tablets:

Drug	Reference product	Originator	General dosage-form profile
Lovastatin	Mevacor	Merck	Immediate-release tablet
Simvastatin	Zocor	Merck	Immediate-release tablet
Pravastatin	Pravachol	Bristol-Myers Squibb	Immediate-release tablet
Mevastatin	No established U.S. reference product	Not broadly commercialized in the U.S.	Not a major U.S. Orange Book product

A conventional immediate-release generic would not ordinarily practice the claimed controlled-release architecture. The patent therefore had greater relevance to a controlled-release or reformulated statin product than to standard ANDAs for immediate-release lovastatin, simvastatin or pravastatin.

Were Paragraph IV challenges relevant?

Paragraph IV litigation would have been relevant only while the patent was listed, unexpired and tied to an approved product or an ANDA-relevant formulation.

Because the patent expired in 2017:

A new ANDA applicant does not need to make a Paragraph IV challenge to this patent as a live blocking right.
A certification strategy for any historical ANDA would depend on the patent’s Orange Book listing and the specific reference product.
The patent’s expiration removes the need to await patent expiry for a current U.S. launch.
A generic applicant could still need to address other formulation, method-of-use or manufacturing patents associated with the relevant product.

No current Paragraph IV barrier arises from U.S. Patent 5,916,595 itself.

Which companies challenged the patent?

The patent’s expiration means that current generic competition does not depend on a surviving challenge to this patent. A reliable attribution of historical Paragraph IV filers, settlements or district-court actions requires a case-level review of FDA ANDA records, PACER and the patent’s prosecution and litigation databases. The patent number and claim text alone do not establish a particular challenger or settlement.

The absence of a current enforceable term also limits the commercial importance of any historical litigation. A settlement involving this patent would not extend exclusivity beyond the statutory patent term unless separate, valid rights were involved.

How strong is the patent estate for a competing statin formulation?

The patent had moderate technical specificity but limited current commercial strength.

Strengths

It claims a complete dosage-form architecture.
It combines core composition and coating composition limitations.
The polymer ratio and coating-weight ranges may have provided formulation-specific protection.
Claims 11 and 12 target identifiable lovastatin and multilayer embodiments.
The claims could have created litigation leverage against a product deliberately designed to reproduce the disclosed release system.

Weaknesses

The patent does not cover the statin molecules themselves.
The claims require a narrow set of excipient and coating features.
Numerical ranges provide straightforward design-around options.
Immediate-release statin products are outside the principal controlled-release concept.
The patent term has expired.
The specification’s disclosure would face prior-art scrutiny from earlier osmotic, enteric and controlled-release tablet patents.

For present-day diligence, the patent should be treated as an expired formulation reference, not as an active exclusionary right.

What formulation patents compete with this patent?

The relevant prior-art and competitive landscape includes several technology groups:

Technology group	Relevance to U.S. 5,916,595
Osmotic pump tablets	Relevant to the swellable core and osmotic-agent limitations
Enteric-coated tablets	Relevant to the inner or outer pH-sensitive layers
Cellulose acetate semipermeable coatings	Relevant to the water-insoluble cellulosic polymer limitation
Methacrylate copolymer coatings	Relevant to the pH-sensitive coating limitation
Polyethylene oxide matrices	Relevant to the swelling and release-control mechanism
Statin immediate-release tablets	Commercially important but generally outside the claimed architecture
Multiparticulate and pellet systems	Potential design-around formats
Extended-release capsules	Potential design-around if no compressed tablet core is used

A competitive product could reduce infringement risk by changing the dosage form, removing the osmotic agent, replacing polyethylene oxide, using a different enteric polymer, changing the coating ratio or using a noncellulosic rate-controlling membrane.

Are biosimilar risks relevant?

No. Lovastatin, simvastatin, pravastatin and mevastatin are small molecules, not biologics. The FDA biosimilar pathway under the Public Health Service Act does not apply.[4]

The relevant competitive pathways are:

ANDA approval for pharmaceutically equivalent generic products;
505(b)(2) approval for reformulated or modified-release products; and
Conventional NDA development for a new controlled-release statin product.

The patent could historically have affected a 505(b)(2) formulation more directly than a conventional immediate-release ANDA because the claimed subject matter is the delivery system.

What generic launch risks remain?

The patent itself creates no current launch delay. Residual risk would come from other rights or regulatory requirements.

Risk category	Current assessment
U.S. 5,916,595 term	No live risk after expiration
Immediate-release generic statin	Low relevance from this patent
Controlled-release statin	Technical relevance, but no enforceable term
Other formulation patents	Must be reviewed separately
Method-of-use patents	Product-specific and indication-specific
Manufacturing patents	Potentially relevant if process claims remain active
FDA exclusivity	Depends on the specific reference product and approval history
505(b)(2) pathway	Possible route for modified-release products
Orange Book patent listing	No current blocking effect from this expired patent

What manufacturing and geographic barriers exist?

The patent was a U.S. right. Its expired U.S. claims do not establish current protection in Europe, Japan, China, Canada or other jurisdictions.

Foreign risk would depend on corresponding national patents, national-phase applications, divisional patents, continuations and separate formulation families. Patent expiration dates could differ by country because of filing dates, patent-term adjustments, supplementary protection certificates and local prosecution events.

Manufacturing know-how may still create practical barriers. The relevant development work includes coating uniformity, pore formation, release testing across pH conditions, polymer molecular weight, tablet hardness, osmotic-agent loading and stability. Those factors can affect product development even when no enforceable patent remains.

What is the commercial and revenue exposure?

The patent’s direct revenue exposure is now zero as an exclusionary right because it has expired. Historical exposure was concentrated in a controlled-release statin product, not in the larger market for standard immediate-release statin tablets.

The largest commercial statin markets were associated with genericized products such as simvastatin, pravastatin and lovastatin. Those markets could be entered through conventional immediate-release products without reproducing the claimed formulation. A company evaluating a controlled-release statin would therefore need to analyze the commercial value of modified release separately from the market value of the underlying active ingredient.

Key Takeaways

U.S. Patent 5,916,595 claims a controlled-release tablet combining an osmotic, swellable core with a pH-sensitive, channel-forming outer coating.
Claim 1 is the broadest claim and requires specific core, coating, ratio and coating-weight limitations.
Claim 11 is a narrow lovastatin formulation claim involving polyoxyethylene polymer, anhydrous lactose and specified coating polymers.
Claim 12 covers a multilayer dosage form with inner and outer pH-sensitive coatings.
The patent does not cover statins generally and does not cover atorvastatin, rosuvastatin, fluvastatin or pitavastatin under the express claims provided.
The patent’s nominal term ended in 2017.
It is not a current Paragraph IV or Orange Book barrier.
Biosimilar analysis is irrelevant because the covered products are small molecules.
Current launch risk would come from other patents, regulatory exclusivity, manufacturing rights or foreign counterparts.
The patent remains relevant as a formulation and prior-art reference, but not as an active U.S. exclusionary right.

FAQs

Can a generic lovastatin tablet infringe U.S. Patent 5,916,595?

A conventional immediate-release lovastatin tablet would generally not satisfy the controlled-release, osmotic-core and multilayer-coating limitations. The patent has also expired.

Does the patent cover simvastatin extended-release tablets?

Claim 2 expressly includes simvastatin, but the product must also satisfy the formulation requirements inherited from claim 1, including the swellable polymer, osmotic agent and specified outer coating.

Could a capsule avoid the patent claims?

A capsule may avoid the “compressed tablet core” limitation, although infringement would depend on the complete product structure and any applicable equivalents analysis.

Does expired patent 5,916,595 prevent a 505(b)(2) statin launch?

No. The expired patent does not independently prevent a 505(b)(2) launch. Other patents, FDA exclusivity and product-specific regulatory requirements may remain relevant.

Is the patent relevant to modern statins such as atorvastatin or rosuvastatin?

Not under the claims provided. The express compound group identifies mevastatin, pravastatin, simvastatin and lovastatin, rather than the newer commercial statins.

References

[1] U.S. Patent No. 5,916,595. (1999). Controlled release formulation. United States Patent and Trademark Office.

[2] United States Code, 35 U.S.C. § 154. (2023). Contents and term of patent; provisional rights.

[3] U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA.

[4] U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	307572	⤷ Start Trial
Australia	1360701	⤷ Start Trial
Australia	1627599	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,916,595

Summary for Patent: 5,916,595