Reversing an earlier US district court decision on Sept. 12, a US appeals court ruled both Teva Pharmaceutical Industries Ltd. (TEVA) and Par Pharmaceuticals could go ahead with plans to market a generic version of GlaxoSmithKline plc (GSK) subsidiary Pronova's blockbuster omega-3 drug Lovaza. Small-cap Irish biopharma Amarin plc (AMRN) , whose only product is a competitor to Lovaza, was rocked by the court’s decision to allow additional competition from generics.

In their ruling, the US appeals court found that Lovaza was made “publicly accessible before the statutory bar date” and that since the patent for Lovaza had expired in March 2013, it was no longer protected from generics.

Lovaza, which contains high doses of omega-3s in the form of, esterified fish oils, has been a smash for GlaxoSmithKline, racking up $2.3 billion in US sales by Aug. 2010.

Amarin had put everything into competing with Lovaza with their sole product, Vascepa. A synthetic derivative of fish oil, had been shown to be even more effective than Lovaza in treating patients with high trigycerides, and finally won FDA approval in July 2012. However, Amarin had chosen to forgo taking on a partner in marketing and distributing the drug, slowing down its march to market.

Even though Vascepa is an effective alternative to Lovaza, with generics now expected to flood the market, it will be much more difficult for Amarin to market their drug.

The giant GlaxoSmithKline was relatively unfazed by the ruling. However, Amarin dropped 5.86 percent on the news to hit $6.75 a share amid four times normal volume.