Fresenius Kabi v. Endo Operations: Levothyroxine Injection Patent Dispute Dismissed
Fresenius Kabi USA LLC filed suit against Endo Operations Limited in New Jersey alleging infringement of three patents covering levothyroxine sodium injection formulations (100–500 mcg/5 mL). The case ended in voluntary dismissal after just 88 days, with no costs or attorneys’ fees awarded to either party.
Rapid voluntary exit in a three-patent levothyroxine injection dispute
On 18 April 2025, Fresenius Kabi USA LLC filed a patent infringement action in the U.S. District Court for the District of New Jersey against Endo Operations Limited, Endo USA Inc., and Endo International PLC. The complaint asserted three patents — US11135190B2, US9782376B1, and US10398669B2 — directed to levothyroxine sodium injection products at concentrations of 20 mcg/mL, 40 mcg/mL, and 100 mcg/mL. This type of action is consistent with Hatch-Waxman ANDA litigation, in which a branded or authorised generic manufacturer seeks to block a competing injectable product from reaching market.
The case closed on 15 July 2025 — just 88 days after filing — when Fresenius Kabi filed a voluntary dismissal notice under Federal Rule of Civil Procedure 41(a)(1)(A)(i). The notice expressly excluded any award of costs or attorneys’ fees to either side. Critically, the public record does not specify whether the dismissal was with or without prejudice. A Rule 41(a)(1)(A)(i) dismissal filed before the defendant has served an answer or motion for summary judgment is, by default under the Federal Rules, without prejudice — but the parties’ own agreement, if any exists, could alter that default.
The 88-day resolution is notably swift for pharmaceutical patent litigation of this type and suggests the parties may have reached a private commercial resolution — such as a licensing arrangement, consent judgment, or market entry agreement — that rendered continued litigation unnecessary. However, no settlement terms appear in the public docket. What remains unknown is whether Endo’s levothyroxine injection product remains blocked, was licensed, or will enter the market, and whether any of the three asserted patents could be re-asserted in future proceedings.
Filing to Voluntary dismissal in 88 days
88 days — resolved well before typical ANDA patent litigation timelines of 2–3 years
Voluntarily dismissed: what the Rule 41 exit means for both parties
Rule 41(a)(1)(A)(i): a plaintiff-controlled early exit
A dismissal under Fed. R. Civ. P. 41(a)(1)(A)(i) allows the plaintiff to exit before the defendant has answered or moved for summary judgment — no court approval required. By default under the Federal Rules, such a dismissal is without prejudice unless the notice itself states otherwise. Here, the notice is silent on prejudice, leaving open the question of whether Fresenius Kabi could refile substantially similar claims against Endo’s levothyroxine product in a future action.
Plaintiff-initiated exitWith or without prejudice? The public record does not say
The dismissal notice does not specify whether it is with or without prejudice. Under the Federal Rules, a Rule 41(a)(1)(A)(i) dismissal is presumed without prejudice — meaning Fresenius Kabi could theoretically refile. However, if the parties entered a confidential settlement or licensing agreement, that private arrangement may contractually preclude refiling. Without access to any side agreement, it is impossible to determine the practical finality of this dismissal from the public record alone.
Prejudice status: unconfirmedEndo avoids merits adjudication — but patent risk may persist
Endo Operations, Endo USA, and Endo International were dismissed without any finding on infringement or validity of the three asserted patents. No injunction issued. No damages were assessed. Whether Endo’s levothyroxine injection product may now freely launch, or is constrained by a private side agreement, is not publicly known. The absence of a merits ruling means Endo cannot point to a judicial finding of non-infringement or invalidity as a shield against future assertion of the same patents.
No merits ruling for defendantSwift exit suggests off-docket resolution in a competitive injectable market
Levothyroxine sodium injection is a critical-care thyroid product with a limited competitive landscape. An 88-day dismissal — before any substantive motion practice — is consistent with a negotiated resolution rather than a litigation defeat. Competitors and payers monitoring this dispute should note that the three Fresenius Kabi patents remain in force and unadjudicated on the merits, preserving enforcement risk for any other party seeking to enter the levothyroxine injection market with a product that reads on these claims.
Patents remain enforceableFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Fresenius Kabi | Individual | Pharmaceutical injectable manufacturer — holder of US11135190B2, US9782376B1, US10398669B2Search in Eureka ↗ |
| Defendant | ENDO OPERATIONS LIMITED | Individual | Endo Operations Limited, specialty pharmaceutical company and ANDA applicant for levothyroxine sodium injectionSearch in Eureka ↗ |
| Plaintiff counsel | Ahmed Muhammad Tan Riaz | Attorney | Counsel for Fresenius KabiSearch in Eureka ↗ |
| Plaintiff law firm | ArentFox Schiff LLP | Law Firm | Representing Fresenius KabiSearch in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | New Jersey District CourtSearch in Eureka ↗ |
Official order — verbatim text
The dismissal notice invokes Rule 41(a)(1)(A)(i) and expressly waives costs and attorneys’ fees on both sides — an atypical bilateral cost waiver that suggests mutual agreement rather than a unilateral plaintiff retreat. The notice names all three Endo entities, indicating a deliberate, coordinated exit covering the full defendant group. No merits determination was made; the patents’ validity and the products’ infringement status remain legally unresolved. The cost-neutrality clause is commercially significant: it removes any financial deterrent to a future renegotiation or re-assertion if a private agreement were to break down.
US11135190B2, US9782376B1 & US10398669B2 — levothyroxine sodium injection formulations
The three asserted patents — US11135190B2 (application no. US16/511220), US9782376B1 (US15/366864), and US10398669B2 (US15/700258) — cover levothyroxine sodium injection products across a range of concentrations: 20 mcg/mL (100 mcg/5 mL), 40 mcg/mL (200 mcg/5 mL), and 100 mcg/mL (500 mcg/5 mL). The application filing dates spanning 2016–2019 suggest a continuation or related prosecution strategy designed to maintain patent protection across successive product iterations. Levothyroxine sodium injection is a synthetic thyroid hormone used intravenously in acute hypothyroidism and myxedema coma, a niche but clinically critical indication with a small number of approved suppliers.
The three-patent assertion stack is strategically significant: it creates overlapping expiry horizons and forces any ANDA challenger to file Paragraph IV certifications against multiple patents simultaneously, increasing litigation cost and delay risk. Fresenius Kabi’s decision to assert all three patents in a single complaint suggests these are the core of a broader enforcement programme. For competitors in the parenteral thyroid hormone market, the continued in-force status of these patents — now unadjudicated — means freedom-to-operate analysis is essential before any formulation, manufacturing, or regulatory filing decision is made.
Should you run an FTO against US11135190B2, US9782376B1 & US10398669B2?
Any pharmaceutical manufacturer, CDMO, or ANDA applicant developing levothyroxine sodium injection products at any concentration should treat these three patents as live enforcement risk. The voluntary dismissal in this case does not constitute a finding of non-infringement or invalidity. If your formulation, manufacturing process, or product concentration overlaps with the claimed subject matter, the absence of a merits ruling means you have no judicial shield. This is especially critical for 505(b)(2) filers who may rely on Fresenius Kabi’s own reference listed drug data.
PatSnap Eureka’s FTO Search Agent can map the full claim scope of US11135190B2, US9782376B1, and US10398669B2, identify related continuation and divisional applications in Fresenius Kabi’s levothyroxine portfolio, and flag prior art relevant to validity challenges. Eureka can also surface prosecution history estoppel factors that may limit claim scope — critical for understanding whether design-around options exist for alternative levothyroxine sodium injection formulations before regulatory submission.
Run a freedom-to-operate analysis on US11135190B2 to assess your product’s exposure
Run FTO in Eureka →Similar levothyroxine and injectable pharmaceutical patent disputes
Cases involving injectable pharmaceutical formulation patents in New Jersey District Court, including Hatch-Waxman ANDA disputes over thyroid hormone and critical-care injectables.
What this case signals for the injectable pharmaceutical IP landscape
A rapid voluntary dismissal in a multi-patent Hatch-Waxman dispute rarely signals weakness — it typically signals resolution on terms the plaintiff preferred.
Unadjudicated patents retain full enforcement value against new entrants
Because the case closed without any ruling on infringement or validity, all three levothyroxine sodium injection patents — US11135190B2, US9782376B1, and US10398669B2 — remain in force and fully assertable. Any ANDA applicant or 505(b)(2) filer whose product reads on these claims should treat this dismissal as a neutral event, not a clearance signal.
88-day lifecycle suggests monitoring for confidential licensing activity
Resolution this early in ANDA litigation — before answers were filed and before any scheduling order — strongly suggests a private commercial arrangement was reached. IP teams at competing injectable manufacturers should monitor FDA Orange Book listings and any ANDA approval updates for Endo’s levothyroxine product as a proxy for understanding what terms may have been agreed.
Kabi v ENDO — key questions answered
The public record does not specify. The dismissal notice filed under Rule 41(a)(1)(A)(i) is silent on prejudice. Under the Federal Rules, a Rule 41(a)(1)(A)(i) dismissal is presumed without prejudice unless the notice states otherwise. However, any private settlement agreement between the parties — which would not appear on the public docket — could contractually restrict refiling.
Fresenius Kabi asserted three U.S. patents: US11135190B2 (application US16/511220), US9782376B1 (application US15/366864), and US10398669B2 (application US15/700258). All three cover levothyroxine sodium injection formulations at concentrations of 20 mcg/mL, 40 mcg/mL, and 100 mcg/mL respectively.
The case resolved in 88 days — well before any answer was filed or substantive motion practice began. This timeline is consistent with a private commercial resolution such as a licensing agreement, consent judgment, or negotiated market entry arrangement. No settlement terms appear in the public record, so the precise reason for dismissal is not publicly known.
Yes. The voluntary dismissal did not include any finding of invalidity, non-infringement, or unenforceability. All three patents — US11135190B2, US9782376B1, and US10398669B2 — remain in force and fully assertable against other parties. Competitors or ANDA applicants whose products read on these claims should not treat this dismissal as a clearance event.
Rule 41(a)(1)(A)(i) allows a plaintiff to voluntarily dismiss an action without court approval before the defendant serves an answer or a motion for summary judgment. In Hatch-Waxman ANDA litigation, this mechanism is often used when parties reach a private resolution — such as a patent licensing or market entry agreement — that makes continued litigation unnecessary. The default legal effect is dismissal without prejudice, meaning the plaintiff could refile, absent a contrary private agreement.
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