08:29 AM EDT, 09/11/2025 (MT Newswires) -- Arrowhead Pharmaceuticals ( ARWR ) said Thursday it filed a complaint for declaratory judgment against Ionis Pharmaceuticals ( IONS ) to defend its potential familial chylomicronemia treatment plozasiran against Ionis' patent infringement allegations.

Arrowhead said plozasiran, which is under review by the US Food and Drug Administration, does not infringe an Ionis patent. Ionis' claims are baseless and its patent is invalid, Arrowhead added.

Arrowhead said it is not claiming any monetary relief in this litigation.

Ionis Pharmaceuticals ( IONS ) did not immediately respond to MT Newswires' request for comment.

Shares of Ionis were down more than 1% in recent premarket activity Thursday, while Arrowhead stock was flat.