---
schema_version: "secwatch.filing_event.v1"
accession: "0000879407-25-000007"
form_type: "8-K"
ticker: "ARWR"
cik: "0000879407"
company_name: "ARROWHEAD PHARMACEUTICALS, INC."
filed_at: "2025-09-11T23:59:59+00:00"
generated_at: "2026-05-17T06:56:38.203735+00:00"
event_type: "litigation"
sentiment: "neutral"
materiality_score: 0.8
calibrated_materiality_score: 0.8
confidence: "high"
source: SEC EDGAR
---

# Arrowhead files declaratory judgment suit against Ionis over '333 patent for plozasiran

## Summary
- Arrowhead filed a declaratory judgment action in Delaware against Ionis claiming the '333 patent is invalid and not infringed by plozasiran.
- Plozasiran is Arrowhead's RNAi therapy for familial chylomicronemia syndrome (FCS); Phase 3 PALISADE study showed up to 80% triglyceride reduction.
- FDA PDUFA action date for plozasiran is November 18, 2025.
- Ionis sent a September 3, 2025 letter alleging patent infringement and threatening suit; Arrowhead acted preemptively.
- Arrowhead's complaint alleges the '333 patent claims are invalid for anticipation and lack of written description/enablement.

## SEC filing metadata
- accession: 0000879407-25-000007
- form_type: 8-K
- ticker: ARWR
- cik: 0000879407
- company_name: ARROWHEAD PHARMACEUTICALS, INC.
- filed_at: 2025-09-11T23:59:59+00:00
- event_type: litigation
- sentiment: neutral
- materiality_score: 0.8
- calibrated_materiality_score: 0.8
- confidence: high
- sec_items: 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/879407/000087940725000007/0000879407-25-000007-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/879407/000087940725000007/arwr-20250910.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0000879407-25-000007
- JSON: https://secwatch.observer/filing/0000879407-25-000007.json
- Plain text: https://secwatch.observer/filing/0000879407-25-000007.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.