Pfizer vs. Somerset Therapeutics: Voluntary Dismissal in Xeljanz Patent Case

Updated on Dec. 9, 2025 | Written by Patsnap Team

Introduction

In a concise patent infringement dispute, Pfizer Inc., C.P. Pharmaceuticals International C.V., PF PRISM C.V., PBG Puerto Rico LLC, and PF PRISM IMB B.V. (collectively, “Plaintiffs”) voluntarily dismissed their claims against Somerset Therapeutics LLC 138 days after filing. The case, involving Pfizer’s drug Xeljanz® (tofacitinib), concluded without prejudice in the Delaware District Court before the defendant served an answer. This procedural termination under Federal Rule 41(a)(1)(A)(i) offers a case study in early-stage pharmaceutical patent litigation strategy and procedural maneuvering.

Case Summary

Case Overview

The Parties

The plaintiffs are Pfizer Inc. and related entities, holding rights to the blockbuster JAK inhibitor Xeljanz®. Somerset Therapeutics LLC is the defendant. The swift dismissal before substantive proceedings suggests this was an early-stage dispute, possibly involving a potential market entrant. To analyze patent landscapes for similar pharmaceutical assets, visit Patsnap Eureka IP.

The Patent at Issue

The asserted patent was reissue patent USRE041783E, which originates from application US12/577790. Reissue patents can be sought to correct errors in an original patent. The claims relate to tofacitinib, the active ingredient in Xeljanz. The case did not proceed to claim construction or validity challenges.

The Accused Product(s)

The complaint identified Pfizer’s 5 mg and 10 mg Xeljanz® tablets as the products at issue. This indicates the litigation likely concerned Somerset’s proposed product that would compete with these dosage forms.

Legal Representation

Plaintiffs were represented by Morris, Nichols, Arsht & Tunnell LLP, a leading Delaware firm for patent litigation, with attorney Megan Elizabeth Dellinger listed as counsel. No defendant counsel was specified in the available data.

Litigation Timeline & Procedural History

The case followed an abbreviated timeline. Filed on May 16, 2025, in the Delaware District Court, it was dismissed on October 1, 2025, lasting 138 days. The docket shows no substantive motions or hearings occurred. The case was assigned to Colm F. Connolly. The dismissal was effected by the plaintiffs under Federal Rule of Civil Procedure 41(a)(1)(A)(i), which permits voluntary dismissal without court order when the defendant has not yet served an answer or motion for summary judgment.

💡 Key Insight: A Rule 41(a)(1)(A)(i) dismissal allows a plaintiff to unilaterally withdraw a lawsuit without prejudice early in proceedings, preserving the right to refile the same claims later.

The Verdict & Legal AnalysisOutcome: Procedural Termination

The verdict was a procedural termination, not a judicial decision on the merits. Specifically, the plaintiffs filed a Notice of Dismissal pursuant to Rule 41(a)(1)(A)(i), dismissing all claims without prejudice. Moreover, the filing confirmed Somerset had not served an answer or motion for summary judgment. Therefore:

• No ruling was issued on patent validity or infringement.
• No damages or injunctive relief was awarded.
• Consequently, the plaintiffs may refile the same claims in the future.

Legal Analysis: Strategic Use of Procedural Rules

The basis of termination—”Dismissed without Prejudice” under Rule 41—illustrates a strategic use of procedural rules. In particular, this mechanism allows a plaintiff to disengage from litigation before significant resources are expended, while retaining all legal rights. However, the case did not reach stages where key patent litigation elements like claim construction, discovery, or expert testimony would be tested. For attorneys, this highlights the importance of understanding procedural options in the early phases of a case. To track litigation trends in pharmaceutical patents, consider using Patsnap Eureka IP.

Strategic Takeaways

For R&D Teams: Furthermore, this case underscores that not all filed lawsuits proceed to substantive resolution. Thus, monitoring case statuses is crucial for accurate freedom to operate (FTO) analysis.

For Patent Holders: A Rule 41 dismissal can serve as a strategic reset, allowing reassessment of enforcement strategy without conceding weakness on the merits.

For Accused Infringers: Conversely, the absence of an answer in this case meant the defendant avoided litigation costs but gained no finality on the infringement allegations.

Industry & Competitive Implications

In the pharmaceutical sector, early voluntary dismissals can reflect various business realities, including changed competitive assessments or alternative resolution pathways. Additionally, the Delaware District Court frequently handles such procedural maneuvers in complex patent cases. This outcome demonstrates that the filing of a patent infringement complaint does not always predict extended, contentious litigation. Moreover, companies operating in competitive generic or biosimilar spaces should note that early dismissals without prejudice do not eliminate patent-based threats. Start your patent research on Patsnap Eureka IP to monitor such dynamic situations.

Key Takeaways

• ⚖️ Procedural Tool: Voluntary dismissal under FRCP 41(a)(1)(A)(i) is a available mechanism for plaintiffs to terminate a case unilaterally before the defendant answers.
• 📊 No Prejudice: A dismissal “without prejudice” preserves the right to refile identical claims, leaving the underlying dispute unresolved.
• 🔬 Strategic Consideration: Accordingly, early case termination can be a strategic choice, not an indication of claim weakness.
• 🏛️ Forum Practice: Ultimately, the Delaware District Court’s docket accommodates such procedural actions efficiently, reinforcing its role in patent disputes.

Explore similar cases on Patsnap Eureka IP for broader context on pharmaceutical patent litigation patterns.

Disclaimer: This article provides analysis based on publicly available case data for informational purposes only. It does not constitute legal advice. For specific legal counsel on patent infringement matters, consult a qualified attorney.