Amarin's (Nasdaq: AMRN) announcement that it had been issued a patent for its triglyceride-reducing drug, AMR101, did nothing for the stock yesterday. The lack of a reaction -- the stock traded down slightly most of the day -- isn't surprising given that the company announced back in March that the U.S. Patent office had issued a Notice of Allowance for the patent. The issuance of the actual patent was widely expected.

But when patents held by Pronova BioPharma were upheld in court later in the day, shares rose quickly and ended with a 6% increase on the day.

Pronova BioPharma's patents don't have any bearing on how long Amarin's AMR101 remains free from direct generic competition, but it indirectly affects the drug. Pronova's patents protect Lovaza, AMR101's direct competitor that Pronova licensed to GlaxoSmithKline (NYSE: GSK). Amarin's drug appears to be better, but if Teva Pharmaceuticals (Nasdaq: TEVA) and Par Pharmaceutical had won their court case, Amarin would have had a hard time launching with cheap generics of Lovaza on the market.

The upheld patents are set to expire in March 2013 and April 2017, but there will be a generic version of Lovaza on the market before then. Pronova settled with Apotex last year, allowing the generic-drug maker to sell its copycat beginning in the first quarter of 2015. With the win in court against the other generic-drug makers, settling with Apotex doesn't look like a particularly good move for Glaxo, Pronova, or even Amarin, but that's the way things go sometimes.

Assuming AMR101 is approved in July, there's plenty of time to get the drug established before it has to face generic competition. I wouldn't be shocked if the sales took a small hit at that point; the same phenomenon happened when Merck's (NYSE: MRK) Zocor went off patent, causing sales of Pfizer's (NYSE: PFE) Lipitor, which is arguably better, to slip. But the lack of generics now is certainly a plus as Amarin hopefully moves ahead with a launch.

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