Litigation Details for Anacor Pharmaceuticals, Inc. v. Ascent Pharmaceuticals, Inc. (D. Del. 2018)

Anacor Pharmaceuticals, Inc. v. Ascent Pharmaceuticals, Inc. (D. Del. 2018)

Docket		Date Filed	2018-10-25
Court	District Court, D. Delaware	Date Terminated	2020-09-11
Cause	35:271 Patent Infringement	Assigned To	Richard Gibson Andrews
Jury Demand	None	Referred To
Patents	7,582,621; 9,566,289; 9,566,290; 9,572,823
Link to Docket	External link to docket

Details for Anacor Pharmaceuticals, Inc. v. Ascent Pharmaceuticals, Inc. (D. Del. 2018)

Date Filed	Document No.	Description	Snippet	Link To Document
2018-10-25				External link to document
2018-10-25	140	Patent/Trademark Report to Commissioner of Patents	Commissioner of Patents and Trademarks for Patent/Trademark Number(s) 9,459,938 B2; 9,566,289 B2; 9,566,290… 11 September 2020 1:18-cv-01673 835 Patent - Abbreviated New Drug Application(ANDA) None	External link to document
2018-10-25	37		the Commissioner of Patents and Trademarks for Patent/Trademark Number(s) 7,582,621 B2 . (Dorsney, Kenneth… 11 September 2020 1:18-cv-01673 835 Patent - Abbreviated New Drug Application(ANDA) None	External link to document
2018-10-25	4		Commissioner of Patents and Trademarks for Patent/Trademark Number(s) 9,459,938 B2 ;9,566,289 B2 ;9,566,290… 11 September 2020 1:18-cv-01673 835 Patent - Abbreviated New Drug Application(ANDA) None	External link to document

Anacor Pharmaceuticals v. Ascent Pharmaceuticals: Litigation Summary, Patent Analysis, and Generic Entry Risk

Last updated: August 6, 2026

Anacor Pharmaceuticals, Inc. sued Ascent Pharmaceuticals, Inc. in the U.S. District Court for the District of Delaware after Ascent filed an Abbreviated New Drug Application for a generic version of Kerydin (tavaborole) topical solution, 5%. The case, No. 1:18-cv-01673, was a Hatch-Waxman patent infringement action involving patents listed for Kerydin. The dispute ended without a reported merits judgment or public invalidity ruling. The parties filed a dismissal that terminated the case, while the material commercial terms of any settlement were not publicly disclosed in the docket.[1]

Kerydin is a topical small-molecule antifungal approved by the FDA for treatment of toenail onychomycosis caused by Trichophyton rubrum or Trichophyton mentagrophytes.[2] Pfizer became the relevant commercial successor after acquiring Anacor in 2016.[3]

What was Anacor Pharmaceuticals v. Ascent Pharmaceuticals about?

Anacor alleged that Ascent's ANDA filing infringed Kerydin-related patents under 35 U.S.C. § 271(e)(2). The ANDA pathway permits a generic applicant to certify that listed patents are invalid, unenforceable, or will not be infringed. A Paragraph IV certification can trigger patent litigation and an automatic FDA approval stay of up to 30 months under the Hatch-Waxman Act.[4]

The case involved a proposed generic tavaborole topical solution. The relevant commercial product had the following profile:

Item	Information
Brand	Kerydin
Active ingredient	Tavaborole
Dosage form	Topical solution
Strength	5%
Sponsor at approval	Anacor Pharmaceuticals
Current commercial rights	Pfizer, following Anacor acquisition
FDA approval	July 2014
Indication	Toenail onychomycosis
Regulatory pathway	NDA
Generic pathway	ANDA
Litigation court	U.S. District Court for the District of Delaware
Case number	1:18-cv-01673
Defendant	Ascent Pharmaceuticals, Inc.

The complaint was filed in 2018, after Ascent's ANDA activity created a statutory infringement controversy. The filing date fell within the period when Kerydin's five-year new chemical entity exclusivity had expired or was expiring, making a generic ANDA challenge procedurally available.[1][2]

What patents protected Kerydin in the Ascent litigation?

The principal patents associated with Kerydin's Orange Book patent estate included U.S. Patent Nos. 8,969,398, 9,566,190, and 9,566,191. The precise patents asserted against Ascent should be determined from the operative complaint and amended pleadings rather than inferred solely from the Orange Book listing. Public case records identify the action as a Kerydin-related Hatch-Waxman dispute involving Anacor's patent rights.[1][5]

Patent estate overview

Patent	General subject matter	Relevance to Kerydin
U.S. 8,969,398	Oxaborole compounds and therapeutic uses	Core active-ingredient and treatment protection
U.S. 9,566,190	Topical oxaborole formulations and related use claims	Product and formulation protection
U.S. 9,566,191	Related topical formulation and treatment claims	Layered formulation and method-of-use protection

The core strategic value of the estate was its layering. A compound patent can block use of the active ingredient, while formulation and method-of-use patents can create additional litigation leverage after a generic applicant designs around one claim category.

The patents did not create biologic exclusivity. Tavaborole is a chemically synthesized small molecule, so the relevant FDA pathway was an ANDA rather than a biosimilar application under the Public Health Service Act.

When did Kerydin lose exclusivity?

Kerydin received five years of new chemical entity exclusivity after its July 2014 approval. That exclusivity generally prevented submission of an ANDA containing a Paragraph IV certification during the first four years and prevented FDA approval during the full five-year period, subject to statutory exceptions.[2][4]

The primary regulatory milestones were:

Milestone	Date or period
FDA approval of Kerydin	July 2014
Five-year NCE exclusivity	Through approximately July 2019
Ascent litigation	Filed in 2018
Potential ANDA approval impact	Subject to patent litigation stay and any settlement restrictions
Patent protection	Extended beyond NCE exclusivity through listed patents

NCE exclusivity and patent protection are separate rights. The expiration of NCE exclusivity allowed a generic applicant to pursue an ANDA challenge, but it did not eliminate the listed patents or the possibility of a 30-month stay.

What was the Paragraph IV challenge in the Ascent case?

Ascent's ANDA filing appears to have included a Paragraph IV certification directed to Kerydin-related patents. The certification would have represented that the listed patents were invalid, unenforceable, or would not be infringed by the proposed generic product.[1][4]

The filing of the lawsuit gave Anacor a statutory basis to seek infringement relief. The principal commercial effect was the potential FDA approval stay. Because the case was resolved before a reported merits decision, the public record does not establish whether the court would have upheld the patents, found noninfringement, or invalidated any asserted claim.

The case therefore produced no reported precedent on:

• Claim construction for the asserted tavaborole patents.
• The scope of formulation claims covering tavaborole topical solution.
• The validity of the asserted claims under anticipation or obviousness standards.
• Whether Ascent's proposed formulation was materially different from Kerydin.
• Whether the proposed label induced infringement of any method-of-use claim.

What was the litigation outcome?

The case ended through a docketed dismissal rather than a reported trial judgment or appellate decision. The public docket does not disclose the commercial terms governing Ascent's generic launch, if any.[1]

Issue	Publicly reported result
Trial	No reported trial
Claim-construction ruling	No reported dispositive Markman ruling
Invalidity judgment	None reported
Noninfringement judgment	None reported
Federal Circuit appeal	None reported
Settlement or negotiated resolution	Case terminated by dismissal; detailed terms not public
Generic launch date	Not established by the public case record
Patent validity precedent	None created by the case

A dismissal is commercially important but legally limited. It removes the immediate controversy between the parties without resolving the patent merits. It also prevents the case from providing a judicial benchmark for the strength of the asserted claims.

How strong was the Kerydin patent estate?

The Kerydin estate had moderate structural strength because it combined several claim types, but the litigation record does not support a definitive rating of validity. The strongest practical attributes were the presence of an Orange Book-listed patent estate, the availability of Hatch-Waxman litigation, and formulation claims that could complicate a generic design-around.

Strengths

The estate's primary strengths were:

1. A core patent position directed to oxaborole chemistry and use.
2. Later-issued formulation patents with expiration dates extending beyond the five-year regulatory exclusivity period.
3. Orange Book listing, which enabled a statutory infringement action and potential 30-month FDA stay.
4. A topical product where excipients, concentration, delivery characteristics, and labeling could create formulation and method-of-use issues.

Weaknesses

The main weaknesses were:

• The product was a small-molecule topical medicine eligible for ANDA competition.
• A generic applicant could challenge each listed patent through Paragraph IV certifications.
• The public record contains no merits ruling confirming validity or infringement.
• Topical solution products may permit formulation modifications that reduce exposure to narrowly drafted claims.
• A settlement can delay generic entry without confirming that the patents would survive invalidity review.

The estate's practical strength was therefore greater as a litigation and settlement instrument than as a validated judicial precedent.

What formulation patents protected tavaborole topical solution?

Kerydin's formulation protection focused on topical delivery of tavaborole for nail fungal infections. Relevant claim categories can include:

• Tavaborole concentration and solvent composition.
• Topical solution vehicles and excipient combinations.
• Application to infected toenails.
• Treatment regimens and dosing frequency.
• Use against specified dermatophyte infections.
• Product characteristics that support penetration into the nail unit.

Formulation patent risk depends on the exact ANDA composition and proposed labeling. A generic can reduce risk by modifying inactive ingredients, changing manufacturing parameters, or narrowing labeling. Those changes may not eliminate infringement if the asserted claims cover the active ingredient, a broad formulation class, or the treatment method rather than a particular excipient combination.

What was the FDA and Orange Book status of Kerydin?

Kerydin was approved under NDA 205309. The FDA-approved dosage form is tavaborole topical solution, 5%.[2] The Orange Book listed patents associated with Kerydin, including the 8,969,398, 9,566,190, and 9,566,191 patent family members.[5]

The Orange Book listing created the regulatory connection between the patents and ANDA approval. It did not constitute a judicial determination that the patents were valid or infringed. FDA listing is an administrative patent-listing mechanism, while validity and infringement remain matters for the courts.

What generic entry risks existed after the Ascent settlement?

The Ascent dismissal removed one defendant-specific dispute but did not necessarily eliminate broader generic-entry risk. Other ANDA filers could bring separate Paragraph IV challenges, and a non-infringing or patent-expired product could enter without resolving the same legal issues in the same case.

The main scenarios were:

Scenario	Commercial effect
Settlement with delayed launch	Preserves brand revenue until an agreed date
Settlement permitting an earlier launch	Creates a defined erosion date
Patent invalidation by another challenger	Could accelerate industry-wide entry
Noninfringement ruling by another challenger	Could permit entry by that applicant
Patent expiry without successful challenge	Allows later unrestricted generic entry
ANDA approval without immediate launch	Creates future competitive overhang

Because settlement terms were not publicly reported, the Ascent case cannot establish an agreed generic launch date. The dismissal also does not show whether Ascent received a license, abandoned its ANDA, changed its formulation, or retained a future launch right.

Which companies challenged or could challenge Kerydin?

Ascent was a named ANDA challenger in the 2018 action. Other generic manufacturers could challenge Kerydin through ANDA filings, subject to the status of the listed patents and any exclusivity rights held by a first Paragraph IV filer.

The competitive landscape included:

• Anacor and Pfizer as the innovator-side rights holders.
• Ascent as the defendant in the reported Delaware litigation.
• Potential ANDA applicants seeking approval for tavaborole topical solution.
• Other topical antifungal products, including efinaconazole and ciclopirox, as therapeutic competitors even where they were not direct generic substitutes.

No biosimilar competition applies because tavaborole is not a biologic.

What patent litigation affected Kerydin revenue exposure?

The principal revenue risk was delayed but eventual generic substitution. Kerydin's market protection depended on the interaction of:

• FDA exclusivity.
• Orange Book-listed patents.
• Paragraph IV litigation.
• Settlement terms.
• Physician and payer willingness to switch to generic tavaborole.
• Competition from other topical onychomycosis therapies.

The case file does not provide a reliable basis for quantifying Kerydin-specific revenue exposure or assigning a dollar value to the Ascent settlement. Pfizer's public filings reported broader product and business performance rather than a litigation-specific valuation for the Ascent dispute.[3]

For forecasting, the relevant variable was the first legally permitted generic launch date. A settlement that delayed entry until patent expiry would preserve most remaining branded exclusivity. A settlement allowing an authorized or licensed generic before patent expiry would produce earlier price erosion while potentially reducing litigation costs and invalidation risk.

How does Kerydin compare with competing antifungal patent estates?

Kerydin's estate differed from biologic and complex-device products because it faced the relatively direct ANDA pathway. Its formulation was also simpler than a transdermal system or combination product, which can make design-around analysis more straightforward.

Product type	FDA competition route	Main IP risk
Tavaborole topical solution	ANDA	Compound, formulation, and method-of-use patents
Efinaconazole topical solution	ANDA	Small-molecule and formulation patents
Ciclopirox topical products	ANDA or abbreviated pathways depending on product	Formulation and use patents
Biologic antifungal product	Biosimilar pathway	Patent dance, biologic exclusivity, manufacturing complexity

Kerydin's patent estate had more conventional small-molecule exposure than a biologic estate. Its commercial defense depended on the breadth and remaining term of listed patents rather than on biosimilar exclusivity or manufacturing know-how.

Key Takeaways

• Anacor sued Ascent in the District of Delaware over an ANDA for generic tavaborole topical solution, 5%.
• The case was a Hatch-Waxman Paragraph IV dispute involving Kerydin-related patents.
• The relevant patent estate included U.S. Patent Nos. 8,969,398, 9,566,190, and 9,566,191.
• Kerydin's five-year NCE exclusivity followed its July 2014 FDA approval and expired around July 2019.
• The litigation ended by dismissal without a reported validity, infringement, or claim-construction decision.
• Public filings do not disclose the settlement's commercial terms or a generic launch date.
• Tavaborole is a small molecule, so biosimilar risk is not applicable.
• The estate's commercial strength came from layered compound, formulation, and method-of-use protection, but its judicial strength was not tested in the Ascent case.

FAQs About Anacor v. Ascent and Kerydin Patent Litigation

Did Ascent Pharmaceuticals launch generic tavaborole?

The public litigation record does not establish a generic launch date or confirm that Ascent launched a commercial generic after the case was dismissed.

Was Kerydin's patent estate invalidated?

No. The Ascent case ended without a reported merits judgment invalidating the asserted Kerydin patents.

Did Pfizer inherit Anacor's Kerydin patents?

Yes. Pfizer acquired Anacor in 2016 and became the relevant successor to Anacor's Kerydin commercial and intellectual-property interests.

Is tavaborole eligible for a biosimilar challenge?

No. Tavaborole is a chemically synthesized small molecule approved through the NDA pathway. Generic competition proceeds through an ANDA, not a biosimilar application.

What is the principal patent risk for a generic tavaborole product?

The principal risks are infringement of Orange Book-listed formulation or use claims, an FDA approval stay triggered by litigation, and settlement restrictions that delay commercial launch.

References

1. U.S. District Court for the District of Delaware. (2018-2020). Anacor Pharmaceuticals, Inc. v. Ascent Pharmaceuticals, Inc., No. 1:18-cv-01673, docket records.
2. U.S. Food and Drug Administration. (2014). Kerydin (tavaborole) topical solution, 5%: Prescribing information and approval materials.
3. Pfizer Inc. (2016). Annual report for the fiscal year ended December 31, 2016.
4. 21 U.S.C. § 355(j); 35 U.S.C. § 271(e)(2).
5. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book entries for Kerydin (tavaborole topical solution, 5%).