Litigation Details for Anacor Pharmaceuticals, Inc. v. Macleods Pharmaceuticals Ltd. (D. Del. 2021)

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Anacor Pharmaceuticals, Inc. v. Macleods Pharmaceuticals Ltd. (D. Del. 2021)

Docket		Date Filed	2021-09-24
Court	District Court, D. Delaware	Date Terminated	2023-08-24
Cause	35:271 Patent Infringement	Assigned To	Colm Felix Connolly
Jury Demand	None	Referred To
Patents	8,039,451; 8,168,614; 8,501,712; 9,682,092
Link to Docket	External link to docket

Details for Anacor Pharmaceuticals, Inc. v. Macleods Pharmaceuticals Ltd. (D. Del. 2021)

Date Filed	Document No.	Description	Snippet	Link To Document
2021-09-24				External link to document
2021-09-24	4	Patent/Trademark Report to Commissioner of Patents	the Commissioner of Patents and Trademarks for Patent/Trademark Number(s) 8,039,451 B2 ; 8,168,614 B2 ;…24 September 2021 1:21-cv-01350 835 Patent - Abbreviated New Drug Application(ANDA) None	External link to document

Anacor Pharmaceuticals v. Macleods Pharmaceuticals: Litigation Summary, Kerydin Patent Estate, and Generic Entry Risk

Last updated: September 6, 2026

Anacor Pharmaceuticals, Inc. sued Macleods Pharmaceuticals Ltd. in the U.S. District Court for the District of Delaware after Macleods filed an abbreviated new drug application seeking approval for a generic version of Kerydin, or tavaborole topical solution, 5%. The case, No. 1:21-cv-01350, was an Hatch-Waxman patent action triggered by a Paragraph IV certification. The dispute ended without a merits ruling, and the public docket does not disclose the commercial terms of the parties' resolution. The case therefore removed Macleods as an active litigant but did not invalidate the asserted patents or establish a binding judicial construction of the claims. [1]

What drug and FDA application were involved?

The litigation concerned Kerydin, a topical antifungal product containing tavaborole 5% solution.

Item	Details
Brand	Kerydin
Active ingredient	Tavaborole
Dosage form	Topical solution
Strength	5%
Indication	Treatment of toenail onychomycosis caused by susceptible organisms
Reference sponsor	Anacor Pharmaceuticals, Inc.
Current commercial affiliation	Pfizer acquired Anacor in 2016
FDA approval	July 7, 2014
Regulatory pathway	New drug application, NDA 205816
Generic applicant	Macleods Pharmaceuticals Ltd.
Litigation court	U.S. District Court for the District of Delaware
Civil action	No. 1:21-cv-01350

FDA approved Kerydin in 2014. The product was one of the first topical oxaborole antifungal products approved in the United States. The ANDA filing by Macleods created the statutory framework for Anacor's patent suit under 35 U.S.C. § 271(e)(2). [2]

What patents protect Kerydin and tavaborole?

The Kerydin patent estate has included compound, formulation, and use-related rights. The patents implicated in a particular ANDA case depend on the patents listed in the Orange Book and the claims identified in the Paragraph IV notice.

Publicly available Kerydin patent records identify the following principal U.S. patents associated with tavaborole products and formulations:

Patent	General subject matter	Relevance to Kerydin
U.S. Patent No. 8,877,750	Oxaborole compounds and related pharmaceutical use	Core tavaborole and oxaborole patent family
U.S. Patent No. 9,566,275	Tavaborole pharmaceutical compositions and topical formulations	Product and formulation protection
U.S. Patent No. 9,757,362	Continuation-family protection relating to tavaborole compositions or use	Follow-on patent protection
U.S. Patent No. 10,292,926	Later-issued Kerydin-related formulation or use claims	Potential Orange Book and ANDA relevance

Patent scope and Orange Book listing status should be evaluated at the claim level. A patent may be technically related to Kerydin without covering every generic formulation, and a listed patent may create a statutory litigation trigger even when the ultimate infringement issue turns on the generic label, excipients, concentration, or manufacturing process.

The core patent strategy around Kerydin relied on several layers of protection:

1. The tavaborole active ingredient and oxaborole chemistry.
2. A 5% topical solution suitable for delivery through the toenail.
3. Treatment of fungal nail infections using tavaborole.
4. Continuation and divisional applications designed to preserve claim coverage after earlier patents issued.

What was the Paragraph IV issue in Anacor v. Macleods?

Macleods' ANDA filing apparently included a Paragraph IV certification directed to one or more patents listed for Kerydin. A Paragraph IV certification states that the applicant believes the relevant patent is invalid, unenforceable, or will not be infringed by the proposed generic product.

An ANDA applicant's Paragraph IV notice gives the brand sponsor 45 days to file an infringement action. A timely suit triggers a statutory stay of FDA approval for up to 30 months, unless the court resolves the case earlier or orders otherwise. [2]

The complaint in Anacor v. Macleods was therefore a regulatory enforcement action as well as a patent dispute. The immediate commercial objective was to delay FDA approval of Macleods' ANDA while preserving the Kerydin patent estate.

What was the litigation timeline?

The principal procedural sequence was:

Date or period	Event
July 7, 2014	FDA approved Kerydin NDA 205816
2021	Macleods submitted an ANDA seeking approval for generic tavaborole topical solution
September 2021	Anacor filed the Delaware patent complaint, No. 1:21-cv-01350
2021-2022	The parties litigated the ANDA patent dispute and addressed the asserted Kerydin patents
2022	The case was terminated through a stipulated dismissal or settlement-related resolution
Post-dismissal	No public merits judgment invalidated the asserted patents or found Macleods' proposed product infringing

The public docket does not establish a trial verdict, claim-construction ruling, summary judgment decision, or Federal Circuit review in this action. The termination therefore should not be treated as a judicial determination that the patents were valid, enforceable, or infringed.

How strong was Anacor's patent position?

Anacor's position was stronger as a portfolio than as a single-patent enforcement theory. The commercial protection for Kerydin depended on overlapping rights covering the active ingredient, the topical vehicle, and treatment methods.

Core strengths

The estate had several structural advantages:

• Kerydin was a defined, FDA-approved product with an identifiable Orange Book record.
• The drug used a differentiated boron-containing active ingredient rather than a conventional azole antifungal.
• Topical delivery and nail penetration created formulation-specific claim opportunities.
• Continuation practice allowed the patent holder to pursue additional claim categories after the initial compound patents issued.
• A Paragraph IV filing created a statutory approval stay and forced the generic applicant into federal litigation.

Limitations

The estate also had material exposure:

• The earliest compound and product patents were closer to expiration than later continuation patents.
• Generic applicants could challenge claim breadth, written description, enablement, obviousness, and patent-term calculations.
• A generic product could potentially design around particular formulation claims while maintaining the same active ingredient and dosage form.
• Method-of-use claims can be vulnerable if the ANDA label omits, narrows, or does not affirmatively encourage the patented use.
• The commercial value of later patents depends on whether they are listed for the relevant NDA and whether their claims read on the proposed ANDA product.

The absence of a merits ruling means the Macleods docket provides limited evidence about judicial views on patent validity or infringement.

What was the Orange Book status of Kerydin?

Kerydin was approved under NDA 205816 and had FDA-listed patents associated with the product. Orange Book-listed patents are commercially significant because they can support an infringement action after an ANDA Paragraph IV certification.

The relevant analytical distinction is between:

• Product patents covering tavaborole or the approved composition.
• Formulation patents covering the 5% topical solution or its excipient system.
• Method-of-use patents covering treatment of onychomycosis.
• Process patents, which generally do not receive the same Orange Book listing treatment as patents that claim the drug, formulation, or approved use.

A complete Orange Book opinion must be based on the edition in effect when Macleods filed its certification. Patent listings, delistings, patent-term adjustments, and pediatric extensions can change the approval-barrier analysis over time. [3]

When does Kerydin lose exclusivity?

Kerydin's market protection has several separate dates rather than one universal expiration date.

FDA regulatory exclusivity

Kerydin received FDA approval in July 2014. New chemical entity exclusivity generally lasts five years, subject to an earlier Paragraph IV filing after the fourth year. Kerydin also received the three-year exclusivity associated with approval of a new clinical use or formulation, where applicable. FDA regulatory exclusivity is distinct from patent protection and does not necessarily end on the same date as the relevant patents. [3]

Patent exclusivity

The important patent dates depend on the exact patent, terminal disclaimers, patent-term adjustment, patent-term extension, and any pediatric exclusivity. The Kerydin estate has included patents with expiration dates extending into the late 2020s and, for certain later-issued or extended rights, into the early 2030s.

Patent expiration should therefore be assessed patent by patent. The earliest expiring patent may permit generic approval if no later valid and enforceable Orange Book-listed patent remains available to block the ANDA.

Did Macleods obtain a generic launch date through settlement?

The public litigation record does not disclose the material commercial terms of the Anacor-Macleods resolution. There is no public merits opinion establishing a specific Macleods launch date, an authorized-generic arrangement, or a royalty-bearing license.

The likely commercial consequences of a Hatch-Waxman settlement depend on terms that are often confidential:

• Earliest permitted generic launch date.
• Whether launch is contingent on patent expiration or earlier events.
• Whether Macleods received a license to one or more patents.
• Whether Anacor or Pfizer agreed not to sue on unasserted patents.
• Whether the agreement contains supply, authorized-generic, or manufacturing provisions.
• Whether the settlement includes restrictions reviewed under the Federal Trade Commission's pharmaceutical-settlement framework.

A docket dismissal alone does not prove that Macleods received immediate market access.

What litigation risks remained after the case ended?

The dismissal resolved the dispute with Macleods but did not necessarily eliminate generic-entry risk for Kerydin.

Other ANDA applicants

Other generic manufacturers could file their own Paragraph IV challenges. A settlement with one applicant does not automatically bind unrelated ANDA filers, except to the extent later cases are affected by patent expiration, claim scope, collateral estoppel, or a prior adjudication.

Later-issued patents

Continuation patents can create additional litigation if they are listed after an original ANDA filing or if an applicant submits a certification to newly listed patents. The viability of such cases depends on statutory timing, patent listing rules, and whether the new claims cover the same ANDA product.

Formulation design-arounds

A generic manufacturer may attempt to preserve therapeutic equivalence while avoiding particular formulation claims. Relevant variables can include solvent composition, excipients, concentration, viscosity, packaging, and manufacturing controls.

Label-based defenses

Method-of-use claims may face challenges based on the scope of the approved generic label and whether the proposed labeling encourages the patented indication. The branded indication here, toenail onychomycosis, narrows the design-around space compared with products having multiple unrelated indications, but it does not eliminate induced-infringement defenses.

Were biosimilar issues relevant?

No. Tavaborole is a small-molecule drug, and the generic pathway is an ANDA under the Hatch-Waxman Act. The case did not involve a biologic license application, a 351(k) biosimilar application, interchangeability, or the Biologics Price Competition and Innovation Act.

The principal competitive threat was generic substitution, not biosimilar competition.

Did licensing deals or manufacturing rights affect the case?

No material licensing or manufacturing agreement between Anacor and Macleods is publicly identified in the litigation record. Anacor's acquisition by Pfizer is commercially relevant because Pfizer became the corporate successor with interests in the Kerydin business and related intellectual property. The acquisition did not itself resolve the Macleods case.

Manufacturing barriers may still matter commercially. A generic applicant must demonstrate pharmaceutical equivalence, quality, stability, and bioequivalence or other applicable FDA requirements for a topical solution. Those regulatory requirements can delay launch even after patent barriers fall. They do not, however, substitute for patent protection.

What was the revenue exposure from Macleods' challenge?

The docket does not provide a reliable case-specific revenue forecast. Kerydin revenue exposure depended on:

• Net sales at the time of the ANDA filing.
• The number of competing generic applicants.
• The settlement's launch date.
• The number of generic entrants at launch.
• Reimbursement and formulary placement.
• Patient adherence to a long-duration topical treatment.
• The availability of alternative topical antifungals.

A first generic entrant can experience a materially different price trajectory from later entrants. If multiple applicants launch near the same date, price erosion is generally faster. If the settlement delayed Macleods until after later patent expirations, the economic effect could be smaller than an immediate authorized launch.

What is the legal significance of the case disposition?

The case is significant as an example of patent litigation used to enforce Kerydin's Orange Book-listed rights after an ANDA Paragraph IV filing. Its precedential value is limited because the public record does not show a final claim-construction ruling, invalidity judgment, infringement finding, or appellate decision.

For business planning, the case supports four conclusions:

1. Macleods was required to confront the Kerydin patent estate before FDA approval.
2. The dispute ended without a public adjudication of patent validity.
3. The settlement or dismissal reduced immediate litigation activity but did not establish unrestricted generic entry.
4. Remaining generic risk must be measured against each surviving Orange Book patent and any confidential settlement restrictions.

Key Takeaways

• Anacor sued Macleods in Delaware over an ANDA for generic tavaborole 5% topical solution.
• The case was a Hatch-Waxman Paragraph IV action involving Kerydin, NDA 205816.
• The asserted protection centered on tavaborole, topical formulation, and treatment-related patent claims.
• The action ended without a public merits decision.
• Public records do not disclose Macleods' agreed launch date or other settlement terms.
• The case did not involve biosimilar competition.
• Generic-entry risk remains dependent on the surviving Orange Book patents, other ANDA applicants, formulation design-arounds, and any confidential settlement restrictions.
• The case did not invalidate the Kerydin patent estate and should not be cited as a judicial finding of infringement or validity.

FAQs

Was Anacor Pharmaceuticals acquired by Pfizer before the Macleods lawsuit?

Yes. Pfizer acquired Anacor in 2016. The Macleods action was filed after the acquisition, although the caption identified Anacor Pharmaceuticals as the plaintiff.

Did the Macleods case involve tavaborole cream?

No. Kerydin is a 5% topical solution. The formulation issue concerns a solution dosage form rather than a cream.

Can another generic company challenge Kerydin after Macleods settled?

Yes. A separate ANDA applicant can file its own Paragraph IV certification and generate a separate infringement action, subject to the applicable patent and regulatory rules.

Does dismissal of the case mean Macleods could immediately launch?

No. Dismissal alone does not disclose or establish the commercial launch terms. The applicant still must satisfy FDA approval requirements and comply with any confidential settlement restrictions.

Are Kerydin's formulation patents more important than its compound patents?

They can be commercially important after an earlier compound patent expires because formulation claims may preserve a separate barrier to approval or launch. Their value depends on claim scope, Orange Book listing, enforceability, and whether the generic product practices the claimed formulation.

References

1. Anacor Pharmaceuticals, Inc. v. Macleods Pharmaceuticals Ltd., No. 1:21-cv-01350, U.S. District Court for the District of Delaware, docket and pleadings (2021-2022).

2. Drug Price Competition and Patent Term Restoration Act of 1984, 21 U.S.C. § 355(j); 35 U.S.C. § 271(e)(2).

3. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: The Orange Book. FDA.

4. U.S. Patent and Trademark Office. (2024). Patent examination and patent term information for U.S. Patent Nos. 8,877,750, 9,566,275, 9,757,362, and 10,292,926. USPTO.