U.S. Patent 6,080,756: Claim Scope, Expiration, Litigation and Patent Landscape for Trovafloxacin Prodrug Polymorphs
U.S. Patent 6,080,756 protects a specific monohydrate polymorph of a trovafloxacin prodrug, its preparation from other polymorphs, and pharmaceutical and therapeutic uses. The patent is a solid-form and manufacturing patent, not a broad composition-of-matter patent covering trovafloxacin itself. Its ordinary patent term has expired, eliminating current U.S. patent exclusivity based on this patent.
What does U.S. Patent 6,080,756 protect?
The patent covers polymorph PII.M, described as a monohydrate of a trovafloxacin prodrug. Claim 1 defines the protected solid form through two elements:
- The chemical structure shown in the patent; and
- A specified X-ray powder diffraction pattern using Cu radiation.
The principal diffraction peaks recited in claim 1 are:
| Peak |
2θ, degrees |
d-spacing, Å |
| 1 |
3.6 |
24.2 |
| 2 |
7.3 |
12.2 |
| 3 |
13.7 |
6.5 |
| 4 |
14.5 |
6.1 |
| 5 |
17.1 |
5.2 |
| 6 |
21.0 |
4.2 |
| 7 |
23.6 |
3.8 |
| 8 |
26.7 |
3.3 |
The claims identify the material as a monohydrate. Claim 10 further narrows the product to a material having approximately 2.7% water content.
The patent is therefore directed to a particular crystalline form rather than every physical form of the prodrug. A product containing the same active chemical entity but having a different crystal structure, amorphous structure, solvate state, or water content would not necessarily fall within claim 1.
The patented prodrug is associated with alatrofloxacin, the injectable prodrug of trovafloxacin. The exact chemical formula and salt state must be determined from the structural drawing and specification of the issued patent because the structural image is not reproduced in the supplied claim text. [1]
How are the claims structured?
Product claim
Claim 1 is the principal product claim. It uses X-ray powder diffraction data as a defining limitation. In an infringement analysis, the accused material would generally need to satisfy both:
- The claimed chemical identity; and
- The claimed crystalline-form characteristics.
The peak list is not merely descriptive background. It is part of the claim definition. Differences in peak positions, relative intensities, hydration state, or solid-form identity could affect infringement analysis.
Claim 10 is narrower than claim 1 because it requires water content of approximately 2.7%. It may be difficult to apply as a standalone commercial screen because water content can vary with humidity, drying conditions, storage, analytical method, and sample history.
Process claims
Claims 2 through 7 protect processes that convert an earlier polymorph into PII.M.
The relevant polymorphs are:
- PI, the starting polymorph;
- PII, an intermediate polymorph; and
- PII.M, the monohydrate end product.
The patent identifies PII by a separate diffraction pattern:
| Peak |
2θ, degrees |
d-spacing, Å |
| 1 |
3.4 |
26.0 |
| 2 |
6.8 |
13.1 |
| 3 |
13.5 |
6.6 |
| 4 |
16.8 |
5.3 |
| 5 |
19.6 |
4.5 |
| 6 |
20.3 |
4.4 |
| 7 |
23.1 |
3.8 |
| 8 |
25.7 |
3.5 |
| 9 |
27.8 |
3.2 |
Claim 5 separately describes conversion of PI directly into PII.M using an organic solvent containing water. Claims 3, 4, 6 and 7 narrow the solvent conditions. The specifically claimed solvent class includes:
- C1-C6 alkyl esters of C1-C6 alkanoic acids;
- C1-C6 alkanols; and
- Ethyl acetate as the expressly preferred solvent.
The process claims are important because they may reach manufacturing conduct even where the final product is not sold under a process label. Their practical value depends on whether the accused process uses the claimed polymorph sequence and solvent conditions.
What formulations and methods of use are protected?
Pharmaceutical composition
Claim 9 covers a pharmaceutical composition containing:
- A bacterial-infection-treating amount of PII.M; and
- A pharmaceutically acceptable carrier.
The claim is broad as to the carrier but narrow as to the active solid form. It does not expressly limit the dosage form to tablets, capsules, injectables, or any other particular presentation.
Therapeutic method
Claim 8 covers administration of the claimed prodrug to a mammal to treat bacterial infection. The claim is not limited to a named bacterial species, dosing schedule, route of administration, or particular infection site in the supplied text.
The method claim is narrower in practice than a broad trovafloxacin composition claim because it requires administration of the claimed polymorph. A product using the same active molecule in a different form could raise a separate chemical-equivalence issue but would not automatically satisfy the polymorph limitation.
How many patents cover this polymorph?
The supplied record establishes one directly relevant U.S. patent: U.S. Patent 6,080,756. Its claim set is concentrated around the PII.M monohydrate and its manufacture.
| Patent |
Subject matter |
Key claims |
Status |
| U.S. 6,080,756 |
Trovafloxacin prodrug polymorph PII.M |
Solid form, conversion processes, composition, treatment method |
Expired |
The patent should be separated from earlier or unrelated patents that may cover:
- The trovafloxacin parent molecule;
- Other quinolone compounds;
- The alatrofloxacin prodrug generally;
- Salts or solvates other than PII.M;
- Injectable formulations;
- Broad antibacterial methods;
- Manufacturing intermediates.
Those rights, if any, would not be established by the claims supplied for U.S. 6,080,756.
When did U.S. Patent 6,080,756 lose exclusivity?
The patent was issued on June 27, 2000. [1] Its ordinary U.S. term was governed by the post-1995 patent-term regime, under which the term generally runs 20 years from the earliest effective U.S. nonprovisional filing date, subject to patent-term adjustment and any applicable extension.
The ordinary term endpoint associated with the patent is in 2018. No current enforceable exclusivity under U.S. Patent 6,080,756 remains in 2026.
| Event |
Date or period |
| Patent issued |
June 27, 2000 |
| Ordinary 20-year term endpoint |
2018 period |
| Current status |
Expired |
| Remaining U.S. patent term in 2026 |
None |
Patent expiration does not invalidate historical infringement claims arising during the enforceable term. It does, however, prevent the patent owner from using this patent to block a new U.S. launch today.
What is the Orange Book status of the patent?
Trovafloxacin was marketed in the United States under the brand Trovan. Alatrofloxacin was the injectable prodrug associated with the intravenous product. The FDA later restricted and withdrew trovafloxacin-related products because of serious hepatic toxicity concerns. [2][3]
U.S. Patent 6,080,756 is not a current source of Orange Book exclusivity. Orange Book listing and patent enforceability are separate issues:
- A patent may be listed while still subject to later expiration.
- Expiration removes the patent barrier even if historical listing data remains.
- A withdrawn or discontinued reference product can create separate regulatory barriers for an ANDA applicant.
- A patent covering a polymorph does not establish that FDA would accept a generic application for the same product.
The commercial and regulatory status of Trovan materially reduces the practical value of this patent landscape. The FDA’s withdrawal history is more significant for a potential entrant than the expired polymorph patent. [2][3]
Were there Paragraph IV challenges or patent settlements?
No Paragraph IV challenge, Hatch-Waxman settlement, or U.S. patent litigation outcome is established by the supplied patent record.
Because U.S. Patent 6,080,756 has expired, a current Paragraph IV certification directed solely to this patent would not create a meaningful patent challenge. A Paragraph IV strategy would instead need to address any other unexpired patents listed for the reference product, if any, as well as FDA requirements for an ANDA or other application pathway.
A historical Paragraph IV filing against a different trovafloxacin or alatrofloxacin patent would not establish a challenge to U.S. Patent 6,080,756.
How strong is the patent estate?
Claim-strength assessment
| Issue |
Assessment |
| Chemical scope |
Narrow; limited to the claimed prodrug structure |
| Solid-form scope |
Narrow; tied to PII.M and specified XRPD characteristics |
| Process scope |
Moderate where the PI-to-PII.M pathway and solvent conditions are used |
| Formulation scope |
Moderate but dependent on use of PII.M |
| Method-of-use scope |
Broad treatment language, but dependent on the claimed polymorph |
| Current enforceability |
None because the patent has expired |
| Historical design-around risk |
Meaningful for alternative polymorphs, amorphous material, or different hydration states |
The strongest historical protection was against a manufacturer using the same prodrug in PII.M form or converting PI through the claimed solvent-mediated process. The weakest area was broad commercial exclusivity for trovafloxacin therapy, because the patent did not claim all forms of trovafloxacin or all forms of its prodrug.
What generic-entry risks existed?
During the patent term, a generic or follow-on manufacturer could have pursued several design-around strategies:
- Use a different polymorph.
- Use an amorphous form.
- Use a different hydrate or solvate.
- Use a salt or crystalline form outside the claimed chemical identity.
- Use a manufacturing process that avoids the claimed PI-to-PII.M conversion.
- Challenge whether the accused material satisfies the XRPD limitations.
- Challenge the definiteness, written description, enablement, or inherent-characteristics interpretation of the polymorph claims.
The process claims could have narrowed some design-around routes if PII.M was the commercially preferred form. A manufacturer that used PII.M but produced it through a different process would face product-claim exposure under claim 1 even if it avoided claims 2 through 7.
Today, the patent-expiration risk is no longer material. Regulatory and safety barriers dominate any generic-launch analysis.
Are biosimilar issues relevant?
No. Trovafloxacin and alatrofloxacin are small-molecule antibacterial products, not biologics. The relevant regulatory pathway would be an ANDA or another small-molecule pathway, not a biosimilar application under the Public Health Service Act.
The primary technical issues would be pharmaceutical equivalence, bioequivalence, solid-form identity, impurity profile, manufacturing controls, and FDA acceptability of the reference product. A biosimilar analysis is not applicable to this patent.
Were there licensing deals involving the patent?
The patent was assigned to Pfizer or a Pfizer-related entity in the original patent record. [1] No licensing transaction is established by the supplied patent information. Pfizer commercialized Trovan and related trovafloxacin products, but commercialization does not by itself demonstrate a third-party license.
What manufacturing and geographic barriers remain?
U.S. patent protection under U.S. 6,080,756 has expired. The patent does not create current U.S. manufacturing or importation barriers.
Geographic analysis must be conducted jurisdiction by jurisdiction. A U.S. expiration does not establish the status of:
- Foreign counterparts;
- European patents;
- Canadian patents;
- Asian national-phase patents;
- Supplementary protection certificates;
- National patent-term adjustments or extensions.
A foreign counterpart could have had a different expiration date, claim set, opposition history, or legal status. U.S. Patent 6,080,756 alone cannot establish worldwide freedom to operate.
What is the commercial exposure?
The commercial exposure associated with this patent is effectively zero today because:
- The patent has expired;
- Trovan-related products faced serious safety restrictions;
- FDA action reduced or eliminated the normal commercial value of the reference product;
- No active biosimilar market exists; and
- A generic entrant would face regulatory and commercial hurdles unrelated to this expired patent.
Historically, the patent had value as a lifecycle-management asset for a preferred injectable prodrug solid form. Its value would have depended on whether PII.M improved stability, manufacturability, solubility, handling, or product consistency compared with PI or other forms.
Key Takeaways
- U.S. Patent 6,080,756 is a polymorph and process patent for PII.M, a monohydrate of a trovafloxacin prodrug associated with alatrofloxacin.
- Claim 1 is defined by chemical identity and a specific XRPD pattern.
- Claim 10 narrows the product to approximately 2.7% water content.
- Claims 2 through 7 cover solvent-mediated conversion from PI, through PII in some embodiments, to PII.M.
- Claims 8 and 9 cover treatment of bacterial infection and pharmaceutical compositions containing PII.M.
- The patent is not a broad patent on trovafloxacin itself.
- The patent’s U.S. term expired in the 2018 period.
- No current U.S. exclusivity, Paragraph IV barrier, or biosimilar issue arises from this patent.
- FDA safety and product-withdrawal history are more important than patent protection for any current commercial assessment.
- Foreign counterpart status must be assessed separately.
FAQs
Is PII.M the same as trovafloxacin?
No. PII.M is a monohydrate polymorph of a prodrug associated with trovafloxacin. It is not the parent trovafloxacin molecule itself.
Can a different alatrofloxacin polymorph avoid claim 1?
Potentially. Claim 1 is limited to the claimed chemical entity and PII.M XRPD characteristics. A distinct polymorph, amorphous form, hydrate, or solvate would require separate claim analysis.
Does patent expiration permit immediate marketing of a trovafloxacin product?
No. Patent expiration removes one intellectual-property barrier. FDA approval, product safety, reference-product status, manufacturing controls, and applicable regulatory exclusivities remain separate requirements.
Does claim 9 cover an injectable formulation?
It can potentially cover a pharmaceutical composition containing the claimed PII.M prodrug and a pharmaceutically acceptable carrier. The claim is not expressly limited to injection in the supplied text.
Is an XRPD peak mismatch enough to avoid infringement?
Not necessarily. Infringement depends on the complete claim construction, analytical method, measurement tolerances, chemical identity, and whether the accused material meets the claim limitations under applicable law.
References
-
U.S. Patent No. 6,080,756. (2000). Polymorph of a prodrug of trovafloxacin. U.S. Patent and Trademark Office.
-
U.S. Food and Drug Administration. (1999). Trovan (trovafloxacin mesylate) prescribing information. FDA.
-
U.S. Food and Drug Administration. (2004). FDA announces withdrawal of Trovan from the market. FDA.
