Stifel analyst Derek Archila lowered the firm's price target on Amarin (AMRN) to $8 from $24 and keeps a Hold rating on the shares.

The stock in premarket trading is down 63%, or $8.60, to $4.98.

The negative intellectual property ruling last night is a "serious blow" for Amarin, Archila tells investors in a research note. The analyst would not be buying the shares here given the uncertainty the decision has created around the future of Vascepa sales and, "more importantly," Amarin's near-to-medium term cash runway. Archila expects the company's cash burn needs to be "dramatically cut" ahead of possible generic entry.

Looking forward, it is prudent to assume the ruling stands, meaningful cost cuts will be needed and Vascepa is likely to retain "only modest share in a limited generic market," contends Archila.