Shares of

Anadys Pharmaceuticals

( ANDS) were among the worst-performing health-related stocks Thursday, tumbling 17% after the biopharmaceutical company said its chief executive is planning to leave the company by the end of the year.

Anadys said that Kleanthis Xanthopoulos is resigning so that he can join Enterprise Partners Venture Capital, a San Diego firm. Xanthopoulos, who will serve as a managing director at the venture capital firm, could leave Anadys before the end of the year if a successor is found sooner. The company will initiate a search for a new president and CEO shortly. Xanthopoulos will continue to serve on Anadys' board. The company's shares were trading down $1.46 to $7.02.

Encysive Pharmaceuticals

( ENCY) soared 36% after the drugmaker said the Food and Drug Administration accepted for review its response to a March 24 approvable letter related the company's new drug application for Thelin, a treatment used by patients who suffer from pulmonary arterial hypertension. The FDA is expected to make a decision on the drug on or around July 24. Encysive shares were trading at $6.88, up $1.83.

Shares of

Discovery Labs

(DSCO)

jumped 16% after the biotech company's Surfaxin product received orphan drug status from the FDA for the prevention of bronchopulmonary dysplasia, also known as chronic lung disease, in premature infants. Surfaxin previously received fast-track status from the FDA for the same indication. Shares were trading up 19 cents to $1.40.

Panacos Pharmaceuticals

(PANC)

shares fell modestly after the death of the company's chief executive. Samuel "Skip" Ackerman, 58, suffered an apparent heart attack Wednesday afternoon during a presentation at a conference. "This tragic event comes as a great shock to all of us associated with Panacos and our thoughts are first and foremost with Skip's family at this difficult time," the company said in a press release. Peyton Marshall, the company's chief financial officer, has been named as acting CEO until a permanent replacement is found. Shares were trading down 2 cents to $5.50.

Shares of

Volcano

(VOLC)

jumped 12% on their first day of trading. The company, which makes ultrasound and measurement products used to enhance the diagnosis and treatment of heart disease, priced 6.8 million shares at $8 apiece, raising about $54 million. The pricing came in below the projected range of $10 to $12 a share. The company plans to use proceeds from the offering for marketing, research and development, debt repayment and for general corporate purposes. JP Morgan Securities and Piper Jaffray led the underwriting syndicate. Volcano shares recently changed hands at $8.95, up 95 cents.

Other health care volume movers included

Pfizer

(PFE) - Get Report

, up 11 cents to $23.22;

Millennium Pharmaceuticals

( MLNM), up $1.84 to $11.21;

Johnson & Johnson

(JNJ) - Get Report

, down 14 cents to $61.11;

Boston Scientific

(BSX) - Get Report

, up 19 cents to $19.19;

Amgen

(AMGN) - Get Report

, down 38 cents to $66.97;

Elan

(ELN)

, up $1.21 to $16.46;

Merck

(MRK) - Get Report

, up 48 cents to $33.97;

UnitedHealth Group

(UNH) - Get Report

, down 24 cents to $44.74; and

Bristol-Myers Squibb

(BMY) - Get Report

, up 20 cents to $24.95.