# US Patent 8,436,185: Niraparib Tosylate Patent Scope, Expiration, Orange Book Status and Generic Risk
US Patent 8,436,185 protects niraparib tosylate monohydrate, the active pharmaceutical ingredient used in GSK’s Zejula product. The disclosed claim is narrow in chemical identity but commercially important because it covers the drug substance itself rather than only a formulation or method of treatment. The patent issued May 7, 2013, and has a nominal expiration date of March 21, 2028, subject to any applicable patent-term adjustment or extension recorded by the USPTO.
Niraparib is a PARP inhibitor approved by the FDA for maintenance treatment of certain patients with advanced ovarian, fallopian tube, and primary peritoneal cancers. The original rights were developed by Merck and licensed to Tesaro. GSK acquired Tesaro in 2019 and now commercializes Zejula.
What drug does US Patent 8,436,185 protect?
The claim identifies niraparib as the following salt and hydrate:
(3S)-3-{4-[7-(Aminocarbonyl)-2H-indazol-2-yl]phenyl}piperidinium 4-methylbenzenesulfonate monohydrate
The compound is commonly known as niraparib tosylate monohydrate. Niraparib’s free-base chemical name is commonly represented as 2-{4-[(3S)-piperidin-3-yl]phenyl}-2H-indazole-7-carboxamide.
| Feature |
Claim coverage |
| Core pharmacophore |
2H-indazole |
| Substituent |
7-carboxamide |
| Aryl linkage |
Para-substituted phenyl group |
| Basic side chain |
3-substituted piperidine |
| Stereochemistry |
Named (3S) configuration, with additional stereoisomer language |
| Counterion |
4-methylbenzenesulfonate, commonly called tosylate |
| Solid-state form |
Monohydrate |
| Commercial drug |
Niraparib, marketed as Zejula |
The claim is directed to a defined chemical compound. It does not rely on a therapeutic-use limitation, patient-selection limitation, dosage limitation, or formulation limitation.
How broad is claim 1 of US 8,436,185?
Claim 1 is chemically narrow but potentially strong against manufacture, importation, sale, or use of the claimed niraparib salt hydrate.
Its principal limitations are:
- The molecule must have the specified indazole-phenyl-piperidine structure.
- The indazole must carry a 7-aminocarbonyl substituent.
- The piperidine must be attached through the specified phenyl position.
- The salt must contain 4-methylbenzenesulfonate, or tosylate.
- The claimed material must be a monohydrate.
- The claim includes “a stereoisomer or tautomer thereof.”
The most commercially important element is that the claim covers a pharmaceutical salt hydrate of niraparib, not merely a research compound. A generic manufacturer that produces niraparib tosylate monohydrate as its active ingredient would face a direct infringement theory if the patent remained enforceable and the claim survived validity challenges.
Does the claim cover niraparib free base?
The claim expressly identifies the piperidinium tosylate monohydrate. Niraparib free base is not the same claimed chemical form.
A manufacturer using free-base niraparib could argue that it does not literally practice the salt and monohydrate limitations. That argument would not automatically eliminate infringement risk. The patent owner could assert infringement under the doctrine of equivalents, although the strength of that theory would depend on prosecution history, claim construction, the role of the salt and water molecule, and whether the claimed solid form was presented as materially distinct.
Does the claim cover other niraparib salts?
Other salts, such as hydrochloride, mesylate, fumarate, or free base, are outside the literal scope of the named tosylate claim. The doctrine of equivalents could remain relevant, but salt-selection claims are often evaluated closely because the counterion can affect crystallinity, stability, solubility, manufacturability, and bioavailability.
Does the claim cover anhydrous niraparib tosylate?
The claim specifies monohydrate. Anhydrous niraparib tosylate is not literally the claimed solid form. The infringement analysis would depend on whether the product converts to the monohydrate during manufacture, storage, dissolution, or administration and whether the relevant statutory act involves the claimed form.
When does US Patent 8,436,185 expire?
The patent’s principal term is reported to expire on March 21, 2028. The patent issued from a U.S. application claiming priority to an international development program directed to 2H-indazole compounds. The term calculation is based on the earliest relevant nonprovisional or international filing date, not the provisional priority date.
| Event |
Date |
| Priority development date |
March 21, 2008 |
| U.S. patent issuance |
May 7, 2013 |
| Nominal patent expiration |
March 21, 2028 |
| Expected post-expiration generic opportunity |
Subject to other listed patents, regulatory exclusivity, litigation and approval status |
The effective date can be affected by USPTO patent-term adjustment. Patent-term extension under 35 U.S.C. § 156 is generally limited to qualifying regulatory review periods and must be confirmed from the FDA and USPTO records. The Orange Book remains the controlling commercial reference for listed patent information and pediatric exclusivity.
What is the Orange Book status of niraparib and Zejula?
Zejula is an FDA-approved prescription drug marketed by GSK. The reference product contains niraparib tosylate and is supplied in oral dosage forms, including 100 mg capsules and tablet presentations introduced through later product development.
The Orange Book historically identified US 8,436,185 as a compound patent associated with Zejula. Later patents have been listed for methods of use, formulations, dosage forms, or other aspects of niraparib treatment. A generic applicant must evaluate the complete Orange Book listing, not only the compound patent.
| Regulatory issue |
Relevance |
| Reference product |
Zejula |
| Active ingredient |
Niraparib |
| FDA pathway for generics |
ANDA |
| Patent certification |
Paragraph I, II, III or IV, depending on each listed patent |
| Compound patent |
US 8,436,185 |
| Core market issue |
Whether a generic can launch before or after March 2028 |
| Additional barriers |
Method-of-use patents, formulation patents, regulatory exclusivity and litigation |
A Paragraph IV certification would assert that a listed patent is invalid, unenforceable, or not infringed. GSK could file an infringement action under the Hatch-Waxman framework. A timely suit generally triggers a 30-month stay of ANDA approval, subject to statutory exceptions and court action.
What other patents protect niraparib?
The niraparib estate extends beyond US 8,436,185. The relevant categories are compound, formulation, solid-state, dosage, and method-of-use protection.
Compound patents
US 8,436,185 is the foundational compound patent for niraparib tosylate monohydrate. Its value comes from covering the active pharmaceutical ingredient used in the commercial product.
Method-of-use patents
Later patents have addressed treatment of cancer using niraparib, including maintenance treatment in patients with ovarian, fallopian tube, or primary peritoneal cancer. Some method claims may identify:
- Platinum-sensitive or platinum-resistant disease.
- Patients responding to platinum-based therapy.
- BRCA-mutated or homologous-recombination-deficient tumors.
- Specific maintenance-treatment schedules.
- Dose reductions or patient-management protocols.
Method-of-use claims can be commercially significant after expiration of a compound patent, particularly where an ANDA applicant must use a skinny label to omit patented indications. Their strength depends on whether the generic label, promotional conduct, physician prescribing behavior, or product instructions induce infringement.
Formulation and solid-state patents
Later filings may protect:
- Niraparib tosylate monohydrate.
- Crystalline or polymorphic forms.
- Particle-size distributions.
- Oral capsules or tablets.
- Excipients and dissolution profiles.
- Manufacturing or isolation processes.
A formulation or solid-state patent can create a separate launch barrier even if a generic avoids literal infringement of the original compound claim.
How strong is the patent estate for niraparib?
US 8,436,185 has high commercial relevance because it claims the active drug substance in a defined salt-hydrate form. Its principal limitation is its chemical specificity. The claim does not cover every form of niraparib and does not independently claim every use of niraparib.
| Strength factor |
Assessment |
| Product relevance |
High; the claim maps directly to the commercial active ingredient |
| Chemical breadth |
Limited; it requires a particular tosylate monohydrate |
| Design-around potential |
Moderate; alternatives include free base, other salts and nonmonohydrate forms |
| Litigation leverage |
High before expiration if the generic uses the claimed API form |
| Formulation protection |
Not established by the supplied claim |
| Method protection |
Not established by the supplied claim |
| Post-2028 durability |
Dependent on later patents and regulatory exclusivity |
| Validity exposure |
Typical risks include written description, enablement, obviousness, anticipation and claim-construction disputes |
The stereoisomer and tautomer language increases the textual reach of the claim. The effect is limited by the requirement that the resulting entity remain the specified compound or a legally recognized stereoisomer or tautomer. It does not convert the claim into a broad genus covering unrelated PARP inhibitors.
What patent challenges and litigation affect Zejula?
Generic applicants seeking approval for niraparib can challenge listed patents through Paragraph IV certifications. The likely dispute points are:
- Whether the proposed generic contains niraparib tosylate monohydrate.
- Whether the commercial manufacturing process produces the claimed hydrate.
- Whether the claim is anticipated or obvious in view of earlier indazole PARP inhibitors.
- Whether the specification adequately supports the precise salt and hydrate.
- Whether later use patents are infringed by the proposed label.
- Whether a generic can omit protected indications through a section viii statement.
A Paragraph IV challenge to US 8,436,185 would likely focus on obviousness and the distinction between the claimed salt hydrate and previously disclosed niraparib free base, salts, or crystalline forms. The challenger could argue that selection of tosylate and hydration was routine. GSK would likely rely on selection, stability, crystallinity, pharmaceutical performance, and the absence of a predictable motivation to make the claimed form.
No final adjudication invalidating the supplied claim is identified in the patent record cited here. The practical status of any current ANDA litigation must be determined from the latest FDA Orange Book, Delaware district court docket, and Federal Circuit decisions.
What generic launch scenarios exist for niraparib?
Launch after the compound patent expires
A generic using the same niraparib tosylate monohydrate could launch after the effective expiration of US 8,436,185 if no later patent or regulatory stay blocks approval.
Launch after settlement
GSK and an ANDA applicant could settle by agreeing to a launch date before or after March 2028. Settlement terms may include a license, supply arrangement, delayed entry, or restrictions tied to formulation and indications. Such agreements can materially change the practical launch date without changing the patent expiration date.
Skinny-label launch
A generic may seek approval for unpatented indications while carving out patented uses. This strategy is more relevant to later method-of-use patents than to the compound patent. It cannot avoid the compound patent if the proposed product contains the claimed niraparib tosylate monohydrate during the enforceable term.
Alternative-form launch
A generic could pursue free-base niraparib or a different salt or solid form. This approach faces pharmaceutical-development and regulatory risks because the alternative must demonstrate appropriate quality, bioequivalence, manufacturability, stability and dissolution performance.
How does niraparib patent protection compare with competing PARP inhibitors?
| Drug |
Brand |
Company |
Core patent risk profile |
| Niraparib |
Zejula |
GSK |
Compound salt-hydrate patent plus method and formulation estate |
| Olaparib |
Lynparza |
AstraZeneca/Merck |
Extensive compound, formulation and method-of-use protection |
| Rucaparib |
Rubraca |
Clovis/Rigel |
Compound and treatment-method protection, with commercial erosion risk |
| Talazoparib |
Talzenna |
Pfizer |
Compound and method patents, with a more targeted oncology market |
Niraparib’s primary patent advantage is the direct coverage of the marketed salt hydrate. Its primary vulnerability is that the claim does not cover all possible chemical forms of niraparib. The competitive landscape also reduces the commercial value of any single patent because physicians and payers can substitute among PARP inhibitors when clinical labeling and reimbursement permit.
What revenue exposure is tied to US 8,436,185?
The patent protects the active ingredient in Zejula, so its commercial relevance is substantially greater than a patent covering a secondary formulation or narrow dosing method. Revenue exposure includes:
- U.S. sales of Zejula capsules and tablets.
- Maintenance treatment in ovarian, fallopian tube and primary peritoneal cancer.
- Ongoing use under approved labeling before generic entry.
- Price erosion after the first therapeutically equivalent generic.
- Spillover effects on international markets where corresponding family patents expire at different times.
The first approved generic can produce rapid net-price erosion, although the magnitude depends on the number of entrants, payer contracting, authorized generic activity, inventory levels, and the survival of later formulation or use patents.
Geographic coverage and international patent families
US 8,436,185 provides protection only in the United States. Parallel rights may exist in Europe, Japan, Canada, Australia and other jurisdictions through the related international patent family. Each jurisdiction applies separate novelty, inventive-step, sufficiency, patent-term and litigation standards.
International diligence should compare:
- Priority and national-phase filings.
- Granted claims in each market.
- Supplementary protection certificates in Europe.
- Patent-term extensions.
- Opposition or invalidity proceedings.
- Local product approvals.
- Generic filing and launch rules.
A U.S. expiration date cannot be used as a proxy for the international loss-of-exclusivity date.
Key Takeaways
- US 8,436,185 claims niraparib tosylate monohydrate, the active drug substance associated with Zejula.
- The supplied claim is narrow in structure but commercially powerful because it targets the pharmaceutical ingredient itself.
- The claim does not expressly cover every niraparib salt, the free base, every formulation, or every therapeutic use.
- The nominal expiration date is March 21, 2028.
- Generic applicants using the same tosylate monohydrate would face direct infringement risk before expiration.
- Free-base, alternative-salt and nonmonohydrate strategies may offer design-around theories but create regulatory and technical risks.
- Later method-of-use, formulation and solid-state patents may extend practical market protection beyond the compound patent.
- Paragraph IV litigation, settlements, skinny-label strategies and later Orange Book listings will determine the actual generic launch timetable.
- GSK’s control of the Tesaro-originated niraparib program gives it the commercial position associated with the patent estate.
FAQs About US Patent 8,436,185 and Niraparib
Is US 8,436,185 a formulation patent?
No. The supplied claim is a composition-of-matter claim to niraparib tosylate monohydrate. It does not claim a capsule, tablet, excipient system or dissolution profile.
Can a generic avoid US 8,436,185 by using niraparib free base?
Potentially, because free base does not literally contain the claimed tosylate counterion or monohydrate. The generic would still need to address equivalence theories, regulatory requirements and other niraparib patents.
Does US 8,436,185 cover the 3R enantiomer?
The claim identifies the 3S compound and then recites a stereoisomer-or-tautomer alternative. The precise reach depends on claim construction, but the language is broader than a claim limited solely to one expressly named stereochemical form.
What is the most important validity challenge to the patent?
Obviousness is likely to be the central technical challenge. A challenger would compare earlier 2H-indazole PARP inhibitors and known pharmaceutical salt or hydrate-selection techniques against the claimed compound and its demonstrated properties.
Will generic niraparib launch immediately after March 21, 2028?
Not necessarily. Launch depends on the effective patent term, any remaining Orange Book patents, regulatory exclusivity, Paragraph IV litigation, settlements, regulatory approval timing and the generic’s selected salt or formulation.
