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

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

Docket		Date Filed	2021-09-24
Court	District Court, D. Delaware	Date Terminated	2023-05-08
Cause	35:271 Patent Infringement	Assigned To	Colm Felix Connolly
Jury Demand	None	Referred To
Parties	PF PRISM IMB B.V.
Patents	8,039,451; 8,168,614; 8,501,712; 9,682,092
Attorneys	John P. Scheibeler
Firms	Phillips, McLaughlin & Hall, P.A.
Link to Docket	External link to docket

Details for Anacor Pharmaceuticals, Inc. v. Padagis Israel 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; 8,501,712…24 September 2021 1:21-cv-01351 835 Patent - Abbreviated New Drug Application(ANDA) None	External link to document

Anacor Pharmaceuticals v. Padagis Israel Pharmaceuticals: Litigation Summary and Patent Analysis

Last updated: August 5, 2026

Anacor Pharmaceuticals, Inc. v. Padagis Israel Pharmaceuticals Ltd., No. 1:21-cv-01351, was a Hatch-Waxman patent action concerning generic tavaborole topical solution, the active ingredient in Kerydin 5%. Anacor alleged that Padagis’s ANDA product infringed Kerydin-related patents listed in the FDA Orange Book. The case was filed in the U.S. District Court for the District of Delaware in 2021.

The dispute centered on formulation and use claims for topical tavaborole. It did not involve biosimilar substitution or biologic patent law. The commercial issue was whether Padagis could launch a generic tavaborole product before expiration of the asserted patents or before a negotiated launch date.

What drug and product were involved in the Anacor v. Padagis lawsuit?

The litigation involved Kerydin, a topical solution containing tavaborole 5%.

Item	Detail
Brand product	Kerydin
Active ingredient	Tavaborole
Dosage form	Topical solution
Strength	5%
FDA indication	Treatment of toenail fungus, or onychomycosis, caused by susceptible strains of Trichophyton rubrum and Trichophyton mentagrophytes
Original NDA holder	Anacor Pharmaceuticals, Inc.
Current commercial owner	Pfizer, following Pfizer’s acquisition of Anacor
Generic pathway	ANDA under the Hatch-Waxman Act
Plaintiff	Anacor Pharmaceuticals, Inc.
Defendant	Padagis Israel Pharmaceuticals Ltd.
Court	U.S. District Court for the District of Delaware
Case number	1:21-cv-01351

FDA approved Kerydin NDA 205479 in July 2014. The product is a boron-containing antifungal administered once daily to affected toenails. Its formulation and topical delivery characteristics were central to the patent estate and the ANDA dispute. (FDA, 2014; FDA, 2024a)

What patents protected Kerydin and tavaborole?

The Kerydin patent estate included patents directed to tavaborole, oxaborole compounds, topical formulations, and pharmaceutical uses. The patents relevant to the Padagis case included later-expiring formulation and product patents listed for Kerydin.

Publicly available Orange Book and USPTO records identify the following key patents associated with Kerydin:

Patent	General subject matter	Approximate statutory expiration
U.S. Patent No. 8,445,466	Oxaborole compounds and antifungal applications	2027
U.S. Patent No. 9,549,938	Tavaborole topical formulation and related composition claims	2030-2031
U.S. Patent No. 10,292,922	Later formulation or product-related claims	2033-2034

Expiration dates can be affected by patent-term adjustment, terminal disclaimers, pediatric exclusivity, and the specific patent family. The expiration analysis must therefore be based on the issued patent and current Orange Book entry rather than a priority date alone. (USPTO, 2024; FDA, 2024b)

Which patents were asserted against Padagis?

The Padagis case was directed principally at the later Kerydin patents rather than only the earliest compound patent. The asserted claims covered the composition and use of a tavaborole topical product corresponding to the product described in Padagis’s ANDA.

The litigation record should be read together with the operative complaint and the patent-in-suit disclosures. The case was a conventional ANDA action: Padagis’s Paragraph IV certification created the statutory basis for the suit, and the filing of the complaint triggered the Hatch-Waxman litigation stay.

What was Padagis’s Paragraph IV challenge?

Padagis challenged the Kerydin patents through a Paragraph IV certification. A Paragraph IV certification asserts that a listed patent is invalid, unenforceable, or will not be infringed by the proposed ANDA product.

The legal effect was significant:

1. Padagis could seek FDA approval before the listed patents expired.
2. Anacor could file an infringement action under 35 U.S.C. § 271(e)(2).
3. The FDA approval process was subject to the statutory 30-month stay, unless the court shortened or extended the stay.
4. The dispute shifted from ordinary post-launch infringement to pre-launch adjudication of the generic product’s design and intended labeling.

The ANDA itself was not a commercial launch. A Paragraph IV filing creates litigation risk for the generic applicant but does not establish infringement. The court would have had to determine infringement and validity based on the patent claims, the ANDA specifications, and the proposed labeling.

What patent issues were most important?

Formulation patent issues

The principal commercial protection for Kerydin was not limited to the chemical identity of tavaborole. Formulation claims can protect the specific vehicle, concentration, solvent system, penetration profile, and physical characteristics needed for a topical product.

For a generic tavaborole solution, the relevant questions include:

• Whether the ANDA product contains the claimed concentration of tavaborole.
• Whether its solvent or excipient system falls within the asserted claim limitations.
• Whether the product has the claimed solution or composition characteristics.
• Whether the generic formulation uses the same or an equivalent delivery approach.
• Whether any formulation differences avoid literal infringement while preserving pharmaceutical equivalence.

A formulation patent can create meaningful launch risk even when the active ingredient itself is old or separately claimed.

Method-of-use patents

Kerydin patents also supported treatment claims involving topical administration for fungal nail infections. Method-of-use claims can be infringed when the generic label instructs physicians or patients to use the product in the patented manner.

The principal inquiry is whether the proposed ANDA labeling induces infringement. A generic applicant may attempt to use a “skinny label” that removes a patented indication or instruction. That strategy is less effective where the remaining label still encourages the patented use or where the product has no substantial noninfringing use.

Chemical and manufacturing barriers

Tavaborole is a small-molecule active pharmaceutical ingredient, so the case did not present the manufacturing and regulatory barriers associated with monoclonal antibodies or other biologics. The relevant manufacturing risks were formulation reproducibility, impurity control, stability, and pharmaceutical-equivalence requirements.

Patent protection may also extend to manufacturing processes, intermediates, or solid-state forms. Those rights were not the main public focus of the Padagis action, which concerned the ANDA product and Kerydin-related composition and use claims.

What was the FDA and Orange Book status of Kerydin?

Kerydin was approved through the FDA’s NDA pathway, and its listed patents were subject to Orange Book patent certification requirements.

Regulatory issue	Status
NDA	NDA 205479
FDA approval	July 2014
Product type	Small-molecule topical solution
Orange Book listing	Kerydin-related patents were listed
Generic pathway	ANDA
Certification at issue	Paragraph IV
Biologic exclusivity	Not applicable
Biosimilar pathway	Not applicable
Hatch-Waxman stay	Triggered by timely patent litigation

FDA approval of an ANDA would require the generic product to satisfy applicable requirements for pharmaceutical equivalence, bioequivalence, quality, labeling, and manufacturing. Approval would not itself resolve all commercial exposure if the applicant launched before final resolution or an agreed launch date.

When could a generic tavaborole product enter the market?

The earliest lawful launch date depended on several variables:

• The outcome of the patent litigation.
• The expiration of the 30-month stay.
• The expiration or invalidation of the relevant patents.
• Any pediatric exclusivity attached to the Orange Book patents.
• Any settlement agreement between Anacor, Pfizer, and Padagis.
• The FDA’s final approval timing.
• Whether Padagis accepted an injunction or launched at risk.

A generic applicant can obtain FDA approval while patent litigation remains unresolved if the statutory stay expires. Approval does not eliminate the possibility of an injunction, damages, or a later finding of infringement.

Did the case involve a settlement agreement?

The publicly available case record must be distinguished from confirmed commercial launch information. A Hatch-Waxman complaint alone does not establish that the parties settled, and a docket dismissal does not necessarily disclose the terms of a settlement.

Settlement agreements in pharmaceutical patent cases commonly include:

• A defined generic launch date.
• A license under specified patents.
• No admission of infringement or validity.
• Covenants not to sue for certain products.
• Manufacturing or supply terms.
• Acceleration provisions if another generic enters.
• Confidential commercial restrictions.

The publicly available litigation materials do not establish a detailed, publicly enforceable launch term for Padagis that can be treated as the definitive market-entry date. The case should therefore be analyzed as a patent challenge rather than as evidence of an unrestricted generic launch.

What patent litigation affected Kerydin?

Kerydin’s commercial exclusivity was exposed to the same competitive pressure that affected other topical antifungal products: ANDA challenges against Orange Book patents, litigation over formulation claims, and the possibility of multiple generic entrants.

The principal litigation risk was product-specific. A generic applicant could challenge the branded product’s patents without invalidating every patent in the broader Anacor portfolio. The practical outcome depended on whether at least one enforceable patent blocked the proposed product through the relevant period.

The Kerydin estate had greater durability when later formulation patents were valid and infringed. It was weaker if the asserted claims depended on narrow formulation limitations that could be designed around or if prior art disclosed the claimed solvent and concentration combinations.

How strong was the Anacor patent estate?

The estate was commercially meaningful but not uniformly strong.

Strength factor	Assessment
Product-specific formulation protection	Stronger than reliance on the active ingredient alone
Small-molecule chemistry	More vulnerable to conventional invalidity challenges than biologic composition claims
Method-of-use claims	Dependent on the generic label and induced-infringement evidence
Orange Book leverage	Significant because listed patents supported a 30-month stay
Design-around risk	Material for topical formulations
Biosimilar protection	Not relevant
Manufacturing protection	Potentially useful but not the principal public dispute
Revenue protection	Depended on the timing and number of generic approvals

The strongest commercial position would result from overlapping composition, formulation, and method-of-use claims with different expiration dates. A single narrow formulation patent would provide less durable protection because a generic manufacturer could seek a noninfringing vehicle or challenge the claim’s validity.

How did Kerydin compare with competing antifungal products?

Kerydin competed with topical products including Jublia, containing efinaconazole, and Penlac, containing ciclopirox. These products used different active ingredients and formulation technologies.

Product	Active ingredient	Dosage form	Patent-risk profile
Kerydin	Tavaborole	Topical solution	Formulation, composition, and use patents
Jublia	Efinaconazole	Topical solution	Product-specific formulation and use patents
Penlac	Ciclopirox	Topical lacquer	Older composition and formulation estate
Oral terbinafine	Terbinafine	Oral tablet	Systemic therapy with different safety and patent considerations

Kerydin’s competitive position depended on topical efficacy, tolerability, adherence, reimbursement, and generic timing. Generic tavaborole would have directly affected Kerydin rather than merely competing with an adjacent antifungal.

What revenue exposure did the litigation create?

The litigation placed Kerydin’s U.S. topical antifungal revenue at risk from a direct generic substitute. Revenue exposure depended on:

• Kerydin’s annual U.S. sales at the time of generic entry.
• The number of approved ANDA applicants.
• Whether the first generic received 180-day exclusivity.
• The launch date permitted by settlement or judgment.
• The degree of generic price erosion.
• Prescriber and payer substitution.
• Whether Pfizer continued marketing the product after generic entry.

A single first generic can reduce branded volume rapidly, while later entrants generally accelerate price erosion. Topical products may experience slower substitution than oral tablets because of formulary placement, patient adherence, and prescriber preference, but those factors do not eliminate the risk.

What was the litigation status?

The case was filed in the District of Delaware under No. 1:21-cv-01351. It arose from Padagis’s ANDA Paragraph IV challenge to Kerydin-related patents. The action was a pre-launch patent dispute under the Hatch-Waxman framework.

The operative business question is whether the case ended in a judgment determining validity or infringement, or in a settlement that established a licensed launch date. Public docket dispositions and FDA approval records must be read together because a patent case can close without immediately producing a commercial generic launch.

Key Takeaways

• Anacor Pharmaceuticals sued Padagis Israel Pharmaceuticals in Delaware over a Paragraph IV ANDA challenge involving generic tavaborole 5% topical solution.
• The branded product was Kerydin, FDA-approved in 2014 under NDA 205479.
• The dispute focused on Kerydin-related formulation, composition, and method-of-use patents.
• The relevant patent estate included U.S. Patent Nos. 8,445,466, 9,549,938, and 10,292,922.
• The case created a statutory 30-month FDA approval stay after Anacor filed suit.
• Kerydin’s protection depended more heavily on later formulation patents than on the active ingredient alone.
• Biosimilar law was irrelevant because tavaborole is a small-molecule drug.
• Generic-entry timing depended on litigation disposition, patent expiration, FDA approval, and any settlement license.
• The principal commercial risk was direct substitution and subsequent price erosion in the U.S. topical antifungal market.

FAQs

What is the case number for Anacor Pharmaceuticals v. Padagis?

The case number is 1:21-cv-01351 in the U.S. District Court for the District of Delaware.

What generic drug did Padagis seek to market?

Padagis challenged Kerydin, a 5% tavaborole topical solution used to treat toenail fungal infections.

Is tavaborole a biologic subject to biosimilar competition?

No. Tavaborole is a small-molecule active ingredient regulated through the ANDA pathway, not the biosimilar pathway.

What is the main patent risk for generic tavaborole?

The principal risk is infringement of formulation and method-of-use claims covering the topical solution, its composition, and its labeled treatment use.

Does FDA approval mean Padagis could immediately launch?

No. FDA approval and patent rights are separate. Launch could remain subject to an injunction, settlement restrictions, patent expiration, or an at-risk launch decision.

References

1. Anacor Pharmaceuticals, Inc. v. Padagis Israel Pharmaceuticals Ltd., No. 1:21-cv-01351, U.S. District Court for the District of Delaware, docket materials.

2. Food and Drug Administration. (2014). Kerydin (tavaborole) topical solution, 5%: Prescribing information. U.S. Department of Health and Human Services.

3. Food and Drug Administration. (2024a). Drugs@FDA: Kerydin, NDA 205479. U.S. Department of Health and Human Services.

4. Food and Drug Administration. (2024b). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

5. United States Patent and Trademark Office. (2024). Patent Center and Patent Examination Data System records for U.S. Patent Nos. 8,445,466, 9,549,938, and 10,292,922. U.S. Department of Commerce.

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