---
title: "Arrowhead Pharmaceuticals Files Suit Against Ionis Pharmaceuticals Over Patent Dispute on Investigational Drug Plozasiran"
description: "Arrowhead Pharmaceuticals Inc. has filed a lawsuit against Ionis Pharmaceuticals Inc. in the U.S. District Court for Delaware, seeking to declare Ionis’s U.S. Patent No. 9,593,333 invalid and assertin"
type: "news"
locale: "en"
url: "https://longbridge.com/en/news/256911929.md"
published_at: "2025-09-11T11:30:43.000Z"
---

# Arrowhead Pharmaceuticals Files Suit Against Ionis Pharmaceuticals Over Patent Dispute on Investigational Drug Plozasiran

> Arrowhead Pharmaceuticals Inc. has filed a lawsuit against Ionis Pharmaceuticals Inc. in the U.S. District Court for Delaware, seeking to declare Ionis’s U.S. Patent No. 9,593,333 invalid and asserting that its investigational drug plozasiran does not infringe on this patent. This action follows Ionis's threats of litigation over alleged patent infringement, which Arrowhead claims are unfounded. Arrowhead is committed to developing new treatments for familial chylomicronemia syndrome and plans to defend its position vigorously in court.

Arrowhead Pharmaceuticals Inc. has filed a Complaint for Declaratory Judgment in the United States District Court for the District of Delaware against Ionis Pharmaceuticals Inc. The complaint seeks to establish that Ionis’s U.S. Patent No. 9,593,333 is invalid and that Arrowhead’s investigational drug plozasiran, currently under FDA review, does not infringe on this patent. This legal action follows threats of litigation from Ionis regarding alleged patent infringement. Arrowhead asserts that these allegations are baseless and maintains that its development of plozasiran and its proprietary platform were accomplished independently. The company emphasizes its commitment to providing new treatment options for patients with familial chylomicronemia syndrome (FCS), a rare and severe disease. Arrowhead is confident in its position and plans to vigorously defend its claims in court. Disclaimer: This news brief was created by Public Technologies (PUBT) using generative artificial intelligence. While PUBT strives to provide accurate and timely information, this AI-generated content is for informational purposes only and should not be interpreted as financial, investment, or legal advice. Arrowhead Pharmaceuticals Inc. published the original content used to generate this news brief via Business Wire (Ref. ID: 20250911154263) on September 11, 2025, and is solely responsible for the information contained therein. © Copyright 2025 - Public Technologies (PUBT)

### Related Stocks

- [IONS.US - Ionis Pharma](https://longbridge.com/en/quote/IONS.US.md)
- [ARWR.US - ArrowHead Pharma](https://longbridge.com/en/quote/ARWR.US.md)

## Related News & Research

| Title | Description | URL |
|-------|-------------|-----|
| Ionis Pharmaceuticals CEO Brett P. Monia Reports Sale of Common Shares | Brett P. Monia, CEO of Ionis Pharmaceuticals Inc., reported the sale of common shares of the company. The full filing is | [Link](https://longbridge.com/en/news/275517537.md) |
| Expert Outlook: Ionis Pharmaceuticals Through The Eyes Of 6 Analysts | In the latest quarter, 6 analysts provided mixed ratings for Ionis Pharmaceuticals (NASDAQ:IONS), with an average 12-mon | [Link](https://longbridge.com/en/news/275171994.md) |
| Ionis to hold fourth quarter and full year 2025 financial results webcast \| IONS Stock News | Ionis Pharmaceuticals, Inc. will host a live webcast on February 25 at 11:30 a.m. ET to discuss its fourth quarter and f | [Link](https://longbridge.com/en/news/275602608.md) |
| Ionis Pharmaceuticals CEO Sells Shares | Brett P. Monia, CEO of Ionis Pharmaceuticals, sold 29,430 shares of common stock on February 6, 2026, at a weighted aver | [Link](https://longbridge.com/en/news/275518338.md) |
| Ionis Pharmaceuticals EVP and Chief Scientific Officer Frank Bennett Reports Disposal of Common Shares | Frank C. Bennett, EVP and Chief Scientific Officer of Ionis Pharmaceuticals Inc., reported the disposal of common shares | [Link](https://longbridge.com/en/news/274866559.md) |

---

> **Disclaimer**: This article is for reference only and does not constitute any investment advice.