IP Law Daily, PATENT—Fed. Cir.: Non-infringement judgment in ZTlido topical medical patch patents dispute affirmed, (Aug 6, 2026)

By Carolin Dennis, B.Sc., LL.B., LL.M.

A pharmaceutical manufacturer’s generic product does not infringe the ZTlido patents under a proper construction of the term “dissolving agent.”

A district court did not err in granting judgment of non-infringement as the district court correctly determined that the claimed “dissolving agent,” must dissolve the lidocaine as well as maintain it in a non-crystalline state in the finished patch, the U.S. Court of Appeals for the Federal Circuit has ruled. The Federal Circuit determined that the pharmaceutical manufacturer uses a single solvent, n-heptane, to dissolve the lidocaine and n-heptane, either alone or in combination with any other component, is not equivalent to the claimed “dissolving agent” (Scilex Pharmaceuticals Inc. v. Aveva Drug Delivery Systems, Inc., No. 25-1002 (Fed. Cir. Aug. 4, 2026)).

Scilex Pharmaceuticals Inc. (Scilex) is the exclusive licensee of U.S. Patent Nos. 9,283,174 (’174 patent), 9,931,403 (’403 patent), and 9,925,264 (’264 patent) (collectively, the asserted patents). The asserted patents are directed to non-aqueous lidocaine patch compositions and methods of using such compositions. In May 2022, Aveva Drug Delivery Systems, Inc. (Aveva), a notified Scilex, Itochu Chemical Frontier Corp. (Itochu), and Oishi Koseido Co., Ltd. (Oishi) (collectively, the Scilex plaintiffs) that it had filed an Abbreviated New Drug Application (ANDA) with the U.S. Food and Drug Administration seeking approval of a generic version of ZTlido®, Scilex’s topical lidocaine patch. The Scilex plaintiffs then sued Aveva, alleging that its proposed generic formulation would infringe dependent claim 4 of each of the asserted patents. The Scilex plaintiffs asserted direct infringement under the doctrine of equivalents of claim 4 of the ’174 and ’403 patents and indirect infringement under the doctrine of equivalents of claim 4 of the ’264 patent. They asserted infringement under the doctrine of equivalents, contending that the isostearic acid and oleyl alcohol in Aveva’s patch functioned in the same way to achieve the same result as the claimed two-component dissolving agent consisting of isostearic acid and dipropylene glycol.

The district court determined that, in view of the prosecution history, the “dissolving agent” in the claimed non-aqueous patch had to both “dissolve the lidocaine and prevent crystallization of lidocaine.” The district court stated that Aveva’s patch “used only a single solvent, n-heptane, to dissolve the lidocaine,” and that “n-heptane, either alone or in combination with any other component, was not equivalent to any claimed ‘dissolving agent.’” The district court further determined that prosecution history estoppel and the doctrine of claim vitiation barred the Scilex plaintiffs from asserting that isostearic acid and oleyl alcohol are equivalent to the claimed two component-dissolving agent. Thus, the district court held that the Scilex plaintiffs had not established infringement by Aveva’s generic product. Scilex plaintiffs appealed the judgment of non-infringement entered by the district court.

On appeal, the Federal Circuit noted that the parties agreed that the claimed “dissolving agent” must prevent crystallization of the lidocaine by maintaining it in a dissolved state in the plaster of the patch. However, they disagreed regarding whether the dissolving agent must also dissolve the lidocaine. According to the Scilex plaintiffs, the asserted claims say nothing about how the lidocaine is dissolved during manufacture or the order in which the lidocaine, dissolving agent and other components are combined prior to being incorporated into the plaster of the patch. Therefore, they contended that the district court erred in concluding that a person of ordinary skill in the art “would understand the claimed ‘dissolving agent’ both dissolves the lidocaine and prevents crystallization of lidocaine.” However, the Federal Circuit did not find this argument persuasive and found that the district court correctly determined, “the asserted claims cover a topical patch where lidocaine is dissolved in a combination of an organic acid (isostearic acid) and a polyalcohol (dipropylene glycol).” The Federal Circuit noted that when the phrase “dissolving agent,” is interpreted in view of the specification and prosecution history, it is evident that the term refers to a substance that both dissolves the lidocaine and maintains it in a non-crystalline state in the finished patch.

The Federal Circuit also noted that the specification explains that a problem with prior art non-aqueous patches was that they “had poor permeability to the skin because the lidocaine was not dissolved and was present in a crystalline state.” Therefore, in the claimed invention, “a dissolving agent” and “lidocaine” are “mixed in a plaster” in order to “produce a non-aqueous patch in which the lidocaine is completely dissolved.” This language makes clear that the lidocaine and the dissolving agent are mixed to produce a non-aqueous patch in which the lidocaine is dissolved. Therefore, the Federal Circuit rejected the Scilex plaintiffs’ assertion that the asserted claims did not require the dissolving agent to dissolve the lidocaine.

The Federal Circuit also found that the district court correctly recognized that, “the asserted patents described six examples of the claimed patch,” and the fact that all six examples in the specification described using the “dissolving agent” combination of an organic acid and a polyalcohol to dissolve the lidocaine bolstered the conclusion that the claimed dissolving agent must dissolve the lidocaine and not simply prevent crystallization of the lidocaine in the finished patch. Moreover, the specification identified no substance or substances other than the claimed dissolving agent consisting of an organic acid and a polyalcohol that could appropriately be employed to dissolve the lidocaine in the claimed patch.

The Federal Circuit found that during prosecution of the ’174 patent, the examiner rejected the original claims over two prior art references, including U.S. Patent Application Publication No. 2011/0152377 A1 (Hanma), which describes patches containing lidocaine, an organic acid, and a polyalcohol, and further describes dissolving lidocaine in an ester solvent and/or a polyalcohol solvent. In response, Oishi, the applicant, stated, at least three different times, that in the claimed invention the “lidocaine is dissolved in an organic acid and a polyalcohol,” i.e., in the claimed dissolving agent. The Federal Circuit noted that because Oishi repeatedly and unambiguously represented that the lidocaine was dissolved “in” the claimed dissolving agent, the district court correctly rejected the argument by the Scilex plaintiffs that the claimed dissolving agent need not function to dissolve the lidocaine. On appeal, the Scilex plaintiffs argued that during prosecution “the patentees distinguished the claimed invention from Hanma on the basis that in Hanma, the lidocaine is reacted with an organic acid to form a salt, as opposed to simply dissolving the lidocaine, which does not involve a chemical reaction.” They asserted that the prosecution history does not show that “the patentees clearly and unmistakably distinguished the claimed invention from Hanma on the basis of the order in which the components of the invention are combined or suggest that lidocaine must be dissolved in the dissolving agent alone prior to combination with other components of the patch.” The Federal Circuit determined that even assuming that Oishi’s repeated and consistent statements that the lidocaine is dissolved in the claimed dissolving agent are insufficient to give rise to disclaimer, they nonetheless provide cogent evidence supporting the conclusion that the claimed dissolving agent functions to dissolve the lidocaine.

As the Federal Circuit determined that the district court correctly held that Aveva’s ANDA product did not infringe under a proper construction of the term “dissolving agent,” the Federal Circuit concluded that it need not reach the district court’s alternative holdings. Accordingly, the district court’s judgment was affirmed.

The Case is No. 25-1002.

Judge: Per Curiam.

Attorneys: Jonathan Davies (Norton Rose Fulbright U.S. LLP) for Scilex Pharmaceuticals Inc. Joseph Thomas Jaros (Rakoczy Molino Mazzochi Siwik LLP) for Aveva Drug Delivery Systems, Inc.

Companies: Scilex Pharmaceuticals Inc.; Aveva Drug Delivery Systems, Inc.

Cases: Patent FedCirNews USPTO