What happened

Shares of Amarin (AMRN -0.92%) were 10.4% lower as of 11:20 a.m. EDT on Tuesday. The decline came after the drugmaker announced that John Thero plans to retire as president and CEO effective Aug. 1.

So what

It's not unusual for changes at the CEO level to cause a biotech stock to fall, especially when the CEO's departure is unexpected. But in this case, there don't appear to be any yellow flags with Thero stepping down.

Wood blocks showing an organizational structure with fingers holding the top block

Image source: Getty Images.

Thero was CEO for the last seven years and he's now 60, an age when many people retire. Amarin has already named his successor: Karim Mikhail, senior vice president and head of commercial for Europe, will take the reins in August.

Perhaps the main reason for Amarin's shares sinking today is that Thero's exit could lower the prospects of any merger and acquisition deals over the near term. Amarin is viewed by some as a potential buyout target. 

Now what

The main things to watch with Amarin are the company's launch of Vascepa in Europe and the anticipated approval of the drug in China later this year. Mikhail's track record of more than 20 years at Merck, including leading the big drugmaker's commercial operations for its lipid drugs, seems to make him a good fit to take the baton from Thero in overseeing these efforts.