United States Drug Patent 5,254,556: Claim Scope, Expiration, and Paliperidone Patent Landscape

US Patent 5,254,556 covers ester prodrugs of 9-hydroxyrisperidone, including paliperidone palmitate, together with antipsychotic compositions and treatment methods. The patent issued on October 19, 1993, and its 17-year pre-URAA term expired on October 19, 2010. It no longer creates a US patent barrier to generic paliperidone palmitate. Its commercial importance is historical: it claimed the active ester class later used in long-acting paliperidone products, while later patents addressed injectable suspensions, particle size, dosing regimens, and extended-duration formulations.

What drug does US Patent 5,254,556 cover?

The patent covers esters of the 9-hydroxy group of paliperidone, also known as 9-hydroxyrisperidone.

The relevant chemical structure is:

A 6-fluoro-1,2-benzisoxazole group
A piperidine ring
An ethyl linker
A tetrahydropyridopyrimidinone core
A 9-hydroxy substituent
Esterification of that hydroxyl group with a C2-C20 alkanoic acid

Paliperidone is the active 9-hydroxy metabolite of risperidone. US Patent 5,254,556 does not broadly claim free paliperidone. It claims esterified derivatives of the compound.

Paliperidone palmitate is the C16 ester of paliperidone and falls within the C2-C20 alkanoic acid scope of claim 1. It is the active ingredient in Invega Sustenna, Invega Trinza, and Invega Hafyera products.[1][2][3]

What compounds fall within claim 1?

Claim 1 covers three related categories:

A C2-C20 alkanoic acid ester of the specified 9-hydroxy compound.
A pharmaceutically acceptable acid addition salt of that ester.
An enantiomeric form of the ester or salt.

The claim is a composition-of-matter claim. It does not require a particular dosage form, route of administration, particle size, suspension vehicle, injection interval, or commercial formulation.

What does “C2-C20 alkanoic acid ester” include?

The language covers esters derived from alkanoic acids containing two through 20 carbon atoms. The carbon count is directed to the alkanoic acid portion.

Examples include:

Acid	Carbon count	Relationship to claim 1
Acetic acid	C2	Included
Butyric acid	C4	Included
Hexanoic acid	C6	Included
Octanoic acid	C8	Included
Decanoic acid	C10	Included
Dodecanoic acid	C12	Included
Tetradecanoic acid	C14	Included
Palmitic acid	C16	Included
Stearic acid	C18	Included
Eicosanoic acid	C20	Included

Paliperidone palmitate is the C16 palmitic acid ester. Claim 4 does not list palmitate, but claim 1 independently includes C16 esters.

How do the six claims divide patent protection?

The claims form a product, formulation, method, and species hierarchy.

Claim	Claim type	Scope
1	Composition of matter	C2-C20 paliperidone esters, salts, and enantiomeric forms
2	Pharmaceutical composition	An antipsychotic composition containing a claim 1 compound and inert carrier
3	Method of treatment	Treating psychotic disease in warm-blooded animals with a claim 1 compound
4	Narrow compound species	Octanoate, decanoate, dodecanoate, or tetradecanoate
5	Narrow composition species	Claims 2 compositions using the four listed acids
6	Narrow method species	Claims 3 methods using the four listed acids

Claims 4 through 6 are dependent claims. They narrow the acid component to C8, C10, C12, or C14 species.

Does claim 1 cover paliperidone palmitate?

Yes. Palmitic acid is a C16 alkanoic acid. C16 is within the C2-C20 range recited in claim 1.

The omission of palmitate from claims 4 through 6 does not remove it from claim 1. A C16 ester would be analyzed under claim 1, not under the narrower dependent claims.

Does the patent cover oral paliperidone?

Not as a free compound. The patent's central product claim requires esterification of the 9-hydroxy group.

Oral Invega contains paliperidone, generally formulated as an extended-release tablet. That product is chemically distinct from paliperidone palmitate. US Patent 5,254,556 therefore should not be treated as a patent on all paliperidone products.

Does the patent cover risperidone?

No. Risperidone lacks the claimed 9-hydroxy ester structure. Risperidone is the parent antipsychotic compound, whereas the patent claims ester derivatives of 9-hydroxyrisperidone.

What is the legal scope of claim 1?

Claim 1 is broad at the ester-class level but chemically specific.

Structural limitations

A potentially infringing compound must contain:

The specified substituted benzisoxazole-piperidine pharmacophore;
The tetrahydro-9-hydroxy pyrido[1,2-a]pyrimidin-4-one core;
The methyl substituent;
An ester formed at the 9-hydroxy group;
An alkanoic acid residue containing between two and 20 carbon atoms.

A compound outside the specified core structure would not literally satisfy claim 1. A compound with an ester derived from an acid having more than 20 carbon atoms would also fall outside the express numerical range.

Salt limitation

The claim includes pharmaceutically acceptable acid addition salts. This language expands claim 1 beyond the neutral ester to qualifying salt forms.

It does not mean that every salt of every paliperidone-related molecule is covered. The salt must be associated with the claimed ester compound.

Enantiomer limitation

The claim expressly includes enantiomeric forms. This prevents an argument that only a particular stereochemical form is covered, although the patent's precise stereochemical disclosure and prosecution history remain relevant to claim construction.

Functional limitations

Claim 1 has no therapeutic or formulation limitation. It does not require proof that the compound is administered, injectable, sustained release, or clinically effective. Claims 2 and 3 introduce pharmaceutical and therapeutic context.

What formulations are protected by US Patent 5,254,556?

Claim 2 covers an antipsychotic composition containing:

A claim 1 compound; and
An inert carrier.

The claim is broad enough to encompass pharmaceutical preparations using the claimed ester, but it does not expressly require:

An aqueous vehicle;
A depot suspension;
Nanoparticles;
A specific excipient;
A defined particle-size distribution;
Intramuscular administration;
A particular concentration;
A monthly, three-month, or six-month dosing interval.

Those limitations became important in later paliperidone patents.

The patent therefore provides a foundational compound and broad composition claim. It is not the principal patent source for the technical characteristics of Invega Sustenna or later longer-acting products.

Does claim 2 cover Invega Sustenna?

Historically, paliperidone palmitate in an antipsychotic pharmaceutical composition would fall within the chemical and composition scope of claims 1 and 2. The patent was expired before Invega Sustenna became a major commercial product in the United States.

Current commercial protection for Invega Sustenna depended on later patents and regulatory exclusivity, not on an enforceable right under US Patent 5,254,556.[1][4]

When did US Patent 5,254,556 lose exclusivity?

US Patent 5,254,556 expired on October 19, 2010, based on the 17-year term applicable to the pre-URAA patent.

Event	Date
Patent issued	October 19, 1993
Statutory term	17 years from issue
Expiration	October 19, 2010
Current status	Expired
Current blocking effect	None

Because the patent expired more than a decade ago, it cannot support a present-day US infringement action against a generic manufacturer.

The patent's expiration does not establish freedom to launch every paliperidone palmitate product. Later patents may cover formulation, manufacturing, dosing, or product-specific uses.

What is the Orange Book status of US Patent 5,254,556?

US Patent 5,254,556 is not a current Orange Book barrier for Invega products.

The FDA Orange Book lists patents submitted by NDA holders for approved drug products. A patent that expired in 2010 cannot provide a current period of patent exclusivity. Current Orange Book analysis must be performed product by product, particularly for:

Invega oral extended-release tablets;
Invega Sustenna;
Invega Trinza;
Invega Hafyera.

The relevant later patents for paliperidone palmitate products have addressed injectable dosage forms, suspension properties, dosing schedules, and extended-release administration. The Orange Book remains the controlling source for current listed patents and expiry dates.[4]

Which later patents matter for paliperidone palmitate?

The commercial patent landscape divides into several layers.

Foundational compound patents

US Patent 5,254,556 is the foundational ester patent. It claimed the paliperidone ester class, including C16 palmitate.

Its expiration removed the original composition-of-matter barrier.

Long-acting injectable formulation patents

Later Janssen patents addressed technical features of paliperidone palmitate injections, including:

Aqueous suspensions;
Poorly soluble paliperidone ester particles;
Particle-size ranges;
Injectable concentrations;
Vehicle composition;
Stabilizers and excipients;
Controlled dissolution and release.

US Patent 6,577,563 is widely associated with long-acting injectable formulations of 9-hydroxyrisperidone and was commercially relevant to Invega Sustenna patent disputes.[5]

These patents can create a separate infringement risk even when the foundational compound patent has expired.

Dosing-regimen patents

Later patents addressed:

Initial loading regimens;
Deltoid versus gluteal administration;
Maintenance intervals;
Dose conversion from oral paliperidone or risperidone;
Three-month administration;
Six-month administration.

A generic product can avoid a method-of-use patent by omitting patented indications or dosing instructions from its label, subject to induced-infringement and skinny-label analysis.

Manufacturing patents

Manufacturing and process claims may cover:

Crystallization of paliperidone palmitate;
Control of polymorphic form;
Particle engineering;
Milling or micronization;
Sterile suspension preparation;
Control of residual solvents and impurities.

These rights can affect launch strategy even where a generic developer uses the same active ester but a different manufacturing route.

What patent litigation affects generic paliperidone palmitate?

Generic litigation has centered on later formulation and regimen patents, rather than the expired US Patent 5,254,556.

The principal legal mechanisms are:

An ANDA applicant files a Paragraph IV certification against listed patents.
The NDA holder may sue within 45 days.
The lawsuit can trigger a 30-month stay of FDA approval under Hatch-Waxman.
Settlement terms may establish a licensed or agreed generic entry date.
The precise launch date depends on patent expiry, pediatric exclusivity, court rulings, settlement terms, and FDA approval status.

The expired 5,254,556 patent cannot trigger a current 30-month stay. A Paragraph IV challenge directed solely to that patent would have no practical blocking effect because the patent is no longer enforceable.

What does a Paragraph IV challenge need to address?

A generic paliperidone palmitate applicant would typically assess:

Whether the proposed ester is within a still-live composition claim;
Whether the formulation practices a live injectable-suspension claim;
Whether the proposed label induces infringement of method claims;
Whether a process patent is implicated;
Whether the listed patent is invalid, unenforceable, or not infringed;
Whether a non-infringing formulation or manufacturing process is available.

The 5,254,556 patent would generally be relevant as expired prior art and historical patent-family evidence, not as a current Paragraph IV obstacle.

How strong is the patent estate for paliperidone palmitate?

The estate was strongest when layered:

Protection layer	Historical strength	Current relevance
Paliperidone ester composition	High	Expired
Broad antipsychotic composition	High	Expired
Treatment method	Moderate to high	Expired under 5,254,556
Injectable suspension	High for conforming formulations	Depends on later patent status
Particle size and physical properties	High for narrowly defined products	Product-specific
Dosing regimen	Variable	Label and jurisdiction dependent
Manufacturing process	Variable	Depends on process overlap
Regulatory exclusivity	Time-limited	Separate from patent term

The foundational patent was broad because it covered the chemical class rather than only one commercial ester. The later estate was narrower but more directly tied to the commercial product and delivery system.

How does paliperidone palmitate compare with competing antipsychotics?

Product	Active ingredient	Delivery	Relationship to US 5,254,556
Invega oral	Paliperidone	Extended-release tablet	Free paliperidone, not the claimed ester
Invega Sustenna	Paliperidone palmitate	Monthly injection	C16 ester within claim 1
Invega Trinza	Paliperidone palmitate	Three-month injection	Same active ester, later regimen/formulation issues
Invega Hafyera	Paliperidone palmitate	Six-month injection	Same active ester, later regimen/formulation issues
Risperdal Consta	Risperidone	Long-acting microsphere injection	Different active ingredient
Abilify Maintena	Aripiprazole	Monthly injection	Different chemical and patent estate
Aristada	Aripiprazole lauroxil	Long-acting injection	Different prodrug and patent estate

The patent does not cover competing active ingredients such as aripiprazole, olanzapine, or risperidone.

What generic launch risks exist after expiration?

Expiration of US Patent 5,254,556 removes the foundational chemical barrier but does not eliminate all launch risk.

A generic developer must separately evaluate:

Current Orange Book-listed patents;
Formulation and suspension patents;
Particle-size limitations;
Dosing-regimen claims;
Process patents;
FDA requirements for complex injectable products;
Bioequivalence and therapeutic-equivalence standards;
Device or administration-system rights;
Patent settlements and agreed entry dates;
State-law and induced-infringement exposure.

Paliperidone palmitate is a complex injectable suspension rather than a conventional immediate-release tablet. Manufacturing reproducibility, particle characteristics, sterility, syringeability, and release behavior can create practical barriers independent of the expired composition patent.

What geographic coverage did US Patent 5,254,556 provide?

The patent provided rights only in the United States. Corresponding foreign patent rights would require separate analysis by jurisdiction, including:

European Patent Convention states;
Canada;
Japan;
Australia;
South Korea;
Brazil;
China;
India.

Foreign family members could have different claim scope, expiration dates, prosecution histories, supplementary protection certificates, and validity outcomes. US expiration on October 19, 2010 did not establish simultaneous global expiration.

Key Takeaways

US Patent 5,254,556 claims C2-C20 esters of 9-hydroxyrisperidone, including paliperidone palmitate.
Claim 1 is the key composition-of-matter claim.
Paliperidone palmitate is a C16 ester and falls within claim 1 even though it is not listed in dependent claims 4 through 6.
Claims 2 and 3 cover antipsychotic compositions and treatment methods using the claimed ester.
Claims 4 through 6 narrow the acid component to octanoate, decanoate, dodecanoate, and tetradecanoate.
The patent expired on October 19, 2010.
It is no longer a current US patent barrier and cannot support a present Paragraph IV stay.
Later patents, particularly those covering long-acting injectable suspensions, particle properties, dosing regimens, and manufacturing, are more relevant to current generic launch analysis.
The patent does not broadly cover free paliperidone, risperidone, or competing antipsychotic products.
Expiration of the foundational patent does not eliminate formulation, process, regulatory, or label-based launch risks.

FAQs

Is paliperidone palmitate literally covered by claim 1 of US 5,254,556?

Yes. Paliperidone palmitate is the C16 palmitic acid ester of paliperidone, and claim 1 covers C2-C20 alkanoic acid esters.

Did US Patent 5,254,556 cover Invega Trinza and Invega Hafyera?

Historically, the active paliperidone palmitate in those products falls within the chemical scope of claim 1. The patent expired before those products became current commercial products, so later formulation and dosing patents control present-day patent analysis.

Can an expired patent be used in a Paragraph IV certification?

A generic applicant can address an expired patent in an ANDA certification framework, but the expired patent cannot block FDA approval through a current 30-month stay or support enforceable infringement relief.

Does the patent cover a paliperidone palmitate manufacturing process?

Not expressly based on the claims provided. The claims are directed to the compound, compositions, and treatment methods. A separate process must be claimed in the patent specification or in later patents.

Does claim 1 cover every long-acting antipsychotic injection?

No. It covers specified esters of 9-hydroxyrisperidone. Aripiprazole, risperidone, olanzapine, and other long-acting antipsychotics are outside the claim unless they have the required chemical structure.

References

Janssen Pharmaceutica N.V. (1993). US Patent No. 5,254,556, Esters of 9-hydroxy-risperidone. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2009). Invega Sustenna (paliperidone palmitate) prescribing information. FDA.
U.S. Food and Drug Administration. (2021). Invega Hafyera (paliperidone palmitate) prescribing information. FDA.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
Janssen Pharmaceutica N.V. (2003). US Patent No. 6,577,563, Long-acting injectable formulations of 9-hydroxyrisperidone. United States Patent and Trademark Office.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0368388	⤷ Start Trial	91362	Luxembourg	⤷ Start Trial
European Patent Office	0368388	⤷ Start Trial	07C0044	France	⤷ Start Trial
European Patent Office	0368388	⤷ Start Trial	SPC/GB07/065	United Kingdom	⤷ Start Trial
European Patent Office	0368388	⤷ Start Trial	C300298	Netherlands	⤷ Start Trial
European Patent Office	0368388	⤷ Start Trial	78/2007	Austria	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 5,254,556