Why Amarin's Shares Plunged

Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of biopharma company Amarin (Nasdaq: AMRN  ) were taken down a notch in trading today, losing as much as 12% in intraday trading.

So what: After a rough week last week for Amarin shareholders, the stock was back in the red today. This time around, the story is that investors freaked after finding out that a bunch of insiders were selling shares the day after the company's drug, Vascepa, was approved. Outside shareholders often keep a close eye on what insiders do, and so a wave of insider selling like this has a tendency to cause jitters.

Now what: The news is, indeed, true -- insiders were selling in the wake of the Vascepa approval. The selling was also significant in a few cases. President John Thero, for example, exercised options representing roughly 300,000 shares. OrbiMed, the investment firm of director Carl Gordon, sold more than 300,000 shares.

However, I'm not sure how much investors should be reading into this selling. Thero and the other executives were largely exercising options and selling restricted stock that had been awarded as part of compensation schemes -- Thero's, for instance, were option grants awarded in 2009 and 2010 and are still in the process of vesting. The selling from the executives was also done under 10b5-1 plans, which require them to set up the sale well ahead of time. Thero's for instance, was put in place on June 13.

As for OrbiMed, its sales were also done via 10b5-1 arrangements. In addition, just over a month ago (June 19), OrbiMed was also selling. In that case, it was almost double the amount it sold following the Vascepa approval and at a lower price.

So investors may have a bigger-picture bone to pick in that executives don't want to hold onto the share ownership they're awarded and OrbiMed seems intent on working down its ownership stake. But I'd be hesitant to assume this recent round of selling is a serious vote against the company from insiders.

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