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

Biotechs Aegerion Phamaceuticals (NASDAQ:AEGR) and Isis Pharmaceuticals (NASDAQ:IONS) 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.

David Williamson and Michael Douglass have no position in any stocks mentioned. The Motley Fool recommends Isis Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.