BOSTON ( TheStreet) -- News of a drug's approval or rejection from the U.S. Food and Drug Administration can rock or kill a biotech stock's price. Here are ten companies with drugs facing FDA approval decisions in the first half of this year.

Xenoport ( XNPT)

Drug/indication: Horizant for restless leg syndrome

Approval decision date: Unknown

Xenoport said that the FDA extended the Horizant approval decision date to Feb. 11 from Feb. 9 due to severe winter weather that shut down Washington. Yet the Feb. 11 deadline came and went without any word on the drug's approval. GlaxoSmithKline ( GSK) is Xenoport's marketing partner for Horizant.

Update: The FDA rejected Horizant Wednesday night, citing concerns about a potential link between the drug and pancreatic tumors in rats.

Mannkind ( MNKD)

Drug/indication: Afrezza for diabetes

Approval decision date: Unknown

The Jan. 16 FDA approval decision date for Afrezza was extended because inspections at an insulin manufacturing facility were not yet completed, according to Mannkind. How long the FDA will take to complete its inspection and issue an approval decision for Afrezza, an inhaled insulin device, is not known. Last month, Mannkind executives expressed confidence that the FDA would be able to complete its review within weeks, but that timeline is already past due.

Salix Pharmaceuticals ( SLXP)

Drug/indication: Xifaxan for hepatic encephalopathy

Approval decision date: March 24

Salix will bring Xifaxan in front of an FDA advisory panel on Feb. 23, which will recommend to the FDA whether the drug should be approved or not. As part of these proceedings, the FDA will post its review of Xifaxan on its web site on Feb. 19 or 22.

Shire Pharmaceuticals ( SHPGY)

Drug/indication: Velaglucerase for Gaucher's disease

Approval decision date: Feb. 28

If approved, "Vela" will trigger a marketing battle in Gaucher's disease against well-entrenched competitor and market leader Cerezyme, owned by Genzyme ( GENZ).

Amylin Pharmaceuticals ( AMLN) and Alkermes ( ALKS)

Drug/indication: Exenatide once weekly for diabetes

Approval decision date: March 5

Exenatide once weekly is a long-acting version of Exenatide, a once-daily injectable diabetes drug marketed by Amylin and Eli Lilly ( LLY). Exenatide once weekly was developed with Alkermes' long-acting drug delivery technology; the company will receive royalties on the drug's sales.

InterMune ( ITMN)

Drug/indication: Pirfenidone for idiopathic pulmonary fibrosis

Approval decision date: May 4

Prior to the FDA's approval decision date, an FDA advisory panel will review the safety and efficacy of pirfenidone on March 9. The FDA's review of pirfenidone is expected to post to the agency's web site on March 5 or March 8.

Somaxon Pharmaceuticals ( SOMX)

Drug/indication: Silenor for insomnia

Approval decision date: March 21

The FDA issued a complete response letter for Silenor last December. Somaxon met with the FDA, submitted additional information about the drug's effect in non-elderly patients and now says the agency has all the data it needs to review the drug and issue an approval decision.

Cell Therapeutics ( CTIC)

Drug/indication: Pixantrone for non-Hodgkin's lymphoma

Approval decision date: April 23

The FDA has not yet rescheduled an advisory panel meeting for pixantrone, which was postponed on Feb. 10 due to severe winter weather. Cell Therapeutics executives said that they expect a new advisory panel to convene in late February or early March.

Dendreon ( DNDN)

Drug/indication: Provenge for prostate cancer

Approval decision date: May 1

The FDA has given no indication that it plans to hold an advisory panel meeting to review the Provenge application. A similar panel meeting was held in 2007, which voted to recommend the drug's approval.

Pozen ( POZN)

Drug/indication: Vimovo for pain relief

Approval decision date: April 30

Vimovo combines an acid inhibitor with a non-steroidal anti-inflammatory drug in a single tablet, intended to provide pain relief with fewer gastrointestinal side effects. AztraZeneca ( AZN) is Pozen's marketing partner for Vimovo.

-- Reported by Adam Feuerstein in Boston.

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