Let's take a look at today's top stories in biotech and health care. Keep an eye out for Achillion Pharmaceuticals (NASDAQ:ACHN)Nektar Therapeutics (NASDAQ:NKTR) and Progenics Pharmaceuticals (NASDAQ:PGNX)

Achillion falling back down to Earth
Shares of hepatitis C drugmaker Achillion Pharmaceuticals are down nearly 3% in premarket this morning, continuing yesterday's downturn. Achillion's shares have rallied over the past week by 140% after Merck purchased Idenix Pharmaceuticals for a massive premium in order to gain access to the company's experimental hepatitis C therapies.

Given that Achillion has drugs at a similar stage in their development and a clinical hold was lifted for its lead drug sovaprevir this week, investors naturally saw the company as the next buyout target in the escalating hepatitis C drug war. Now that some of the emotion of Merck's record deal has worn off and no buyer is in sight, Achillion shares are starting to pullback.

My view is that the hepatitis C market space won't turn out to be nearly as profitable for companies following in Gilead's footsteps. As such, you might want to exercise caution with this clinical-stage biotech moving forward. 

Nektar shares jump on panel vote against new safety trials 
Shares of Nektar Therapeutics rose over 11% in after hours trading yesterday following an advisory committee to the Food and Drug Administration recommending that large cardiovascular safety trials for a class of drugs indicated for opioid-induced chronic constipation should not be required prior to approval. 

This development bodes well for Nektar and AstraZeneca's (NYSE:AZN) drug Naloxegol which is set to be reviewed by the FDA by September 16. What's key to understand is that AstraZeneca could have terminated the licensing agreement with Nektar and forced the company to repay up to $70 million in milestone payments. With the additional safety study issue likely out of the way, Nektar can now book this prior payment as revenue and could receive another $175 million in milestone payments. In short, this panel recommendation is stellar news for Nektar. 

Progenics shares moving higher on panel news as well
What's important to remember is that yesterday's advisory committee was the result of an appeal to a complete response letter to Progenics and Salix's Supplemental New Drug Application for Relistor injection for the treatment of opioid-induced constipation in adult patients with chronic, non-cancer pain. In 2012, the FDA requested additional clinical data prior to approving the supplemental NDA, which Salix subsequently appealed. 

According to Progenics' CEO Mark Baker, we should hear about a final decision regarding the appeal within thirty days following this panel recommendation. Shares are up nearly 2% on the back of this news.