Let's take a look at four stocks -- AcelRx (NASDAQ:ACRX), Horizon Pharma (NASDAQ:HZNP), Hospira (UNKNOWN:HSP.DL), and GlaxoSmithKline (NYSE:GSK) -- which could loom large in health care headlines today.

AcelRx plunges after the FDA's rejection of Zalviso
The FDA rejected AcelRx's painkiller dispensing device, Zalviso, late Friday.

The FDA's complete response letter requests additional information regarding the Zalviso System to ensure the proper usage of the device. The FDA was concerned about reducing optical system errors which require premature drug cartridge changes, changes to the instructions, and additional data helping support the product's shelf life.

This is a massive setback for AcelRx, since the company has no marketed products and Zalviso is its most advanced pipeline candidate. Zalviso was expected to generate peak sales of $500 million or so if approved.

Following the rejection, several analysts reduced their price targets on AcelRx. Canaccord Genuity downgraded AcelRx to "hold" and cut its price target in half to $8. RBC Capital dropped its price target from $15 to $12 with an "outperform" rating.

Horizon Pharma plunges after CVS Caremark and Express Scripts' actions
Horizon Pharma has plunged big this morning, after announcing that it was verbally notified that two PBMs (pharmacy benefit managers) -- CVS Caremark and Express Scripts -- will exclude two of the company's drugs, Duexis and Vimovo, from their formularies.

This is a devastating blow to Horizon, since Duexis and Vimovo are two of its three marketed drugs. Duexis generated $13.9 million in revenues last quarter, while Vimovo sales came in at $34 million. Together, the two drugs accounted for over 90% of Horizon's net sales.

Since the changes aren't expected to take effect until 2015, Horizon won't alter its guidance of $270 million to $280 million in net revenues and $80 million to $90 million in adjusted EBITDA for fiscal 2014. However, Horizon admitted that 20% to 30% of Duexis and Vimovo prescriptions could be hit by CVS Caremark and Express Scripts' actions -- indicating a big potential upcoming drop in revenues next year.

Hospira makes a $5 billion bid for Danone's medical nutrition unit
Hospira is now in talks to acquire Danone's medical nutrition unit for around $5 billion, according to a recent Financial Times report. The move could allow Illinois-based Hospira to relocate to France for tax inversion purposes.

Hospira would have to fund a large part of the deal with stock, since tax inversion rules state that the acquired company must receive at least 20% of the merged company's stock. Although tax inversion would be Hospira's main goal, it would also help diversify the company's revenue away from injectable pharmaceuticals and medical devices.

In the past, Nestle and Fresenius were reportedly interested in acquiring Danone's medical nutrition unit, but it's unclear if either company will challenge Hospira's bid. Danone has struggled with an infant milk formula recall in Asia, higher milk prices, and strong euro -- which caused the company's operating profit to drop 20% year-over-year in the first half of 2014.

GSK faces FBI questions, considers spinning off its consumer health care business
GSK employees are now being interviewed by the FBI regarding ongoing bribery allegations in China, according to The Wall Street Journal.

This is just the latest in a long series of problems for GSK -- it is already facing investigations from the SEC and the U.K.'s Serious Fraud Office regarding the company's marketing practices.

Meanwhile, CEO Sir Andrew Witty discussed the possibility of spinning off the company's consumer health care business in the future. Witty noted that there were no concrete plans in the near future, but that it was open to the idea of restructuring the company, especially after GSK lowered its full-year earnings guidance last week. GSK's consumer health care business generated £5.2 billion ($8.8 billion) in revenues last year, accounting for 20% of the company's top line.