Editor's Note: This video was filmed May 7th.

Biotechs Aegerion Phamaceuticals (NASDAQ: AEGR) and Isis Pharmaceuticals (IONS 5.83%) reported earnings last week, and the market reacted pretty negatively to the news --  Isis lost about 4% after reporting, while Aegerion cratered 25%. Looking at the numbers, you might wonder if that was a transcription error.

After all, it was Isis whose revenue dropped to $28 million from $43 million in the year-ago first quarter. Isis also reported a wider loss, with a $0.27 loss per share comparing unfavorably to a $0.02 loss in first quarter of 2013. And Aegerion increased revenue -- in fact, it roughly doubled it to $40 million from $19 million in the year-ago quarter. And the company narrowed its net loss from $0.64 per share to $0.54 per share.

So, what happened?

In the video below, Motley Fool health care analysts Michael Douglass and David Williamson lay out why Aegerion lost so much more than Isis -- how analyst expectations and weaker-than-expected sales of the drug Juxtapid combined to sink the stock last week.