Amarin (Nasdaq: AMRN) keeps swimming toward blockbuster sales. The company announced yesterday that it had reached an agreement with the Food and Drug Administration to run an outcomes study for its fish oil drug, AMR101.

The Special Protocol Assessment ensures that the FDA is comfortable with the trial design and will accept the results assuming nothing unforeseen happens along the way. The 8,000-patient, six-year trial even has a catchy acronym: REDUCE-IT, for Reduction of Cardiovascular Events with EPA - Intervention Trial.

The results of REDUCE-IT are important because they'll allow Amarin to market AMR101 as a treatment to reduce cardiovascular events -- heart attacks, strokes, and the like -- rather than just claiming that the drug reduces triglyceride levels, which the two previous trials showed.

But there's a little more to it than that. The FDA is requiring Amarin to have an outcomes trial substantially under way before it can market the drug to patients with medium levels of triglycerides who are also taking statins such as Pfizer's (NYSE: PFE) Lipitor, AstraZeneca's (NYSE: AZN) Crestor, and Bristol-Myers Squibb's (NYSE: BMY) Pravachol. The agency clearly doesn't want a repeat of Merck's (NYSE: MRK) Vytorin debacle.

The population with medium triglyceride levels is substantially larger than the high-triglyceride patient group, so getting started quickly is important. Amarin is shooting for 50% enrollment in REDUCE-IT by the end of 2012.

The New Drug Application that Amarin plans to submit by the end of September will focus on patients with high levels of triglycerides tested in the first trial, with the second trial just noted on the label. If the FDA is feeling especially generous, it could approve both indications, but investors shouldn't count on it. While it seems rather subjective what the agency deems "substantial" enrollment, that's kind of par for the course.  Sometimes it seems like FDA stands for: For Decisions Arbitrarily.

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