Shares of

Rigel Pharmaceuticals

(RIGL) - Get Report

were among the worst-performing health-related stocks Thursday, plunging 63% after the drug developer's allergy medication failed a phase II clinical trial.

In the trial, R112 didn't meet the study's primary endpoint of showing a statistically significant difference in improving nasal allergy symptoms, when compared with a placebo, over a seven-day period. "We are disappointed in today's results," the company said. "These results are surprising given that the earlier phase II 'Park' study of R112 demonstrated a statistically significant reduction in the symptoms associated with the allergies." Beconase AQ, a

GlaxoSmithKline

(GSK) - Get Report

product that was also compared in the study, was superior to the placebo treatment, Rigel said. Shares of Rigel were trading down $13.75 to $8.17.

Pediatrix Medical Group

( PDX) rose 4% after the contract medical services provider issued a 2006 earnings guidance above Wall Street forecasts. The company sees earnings of $4.76 to $4.86 a share, including items, and $5.35 to $5.45 a share on an adjusted basis. Analysts polled by Thomson First Call expect adjusted earnings of $5.22 a share. Pediatrix's guidance is based on same-unit revenue patient growth of 3% to 5% at neonatal intensive care units staffed by its doctors, as well as contributions from acquisitions. Shares were trading up $3.67 to $88.23.

Lexicon Genetics

(LEXG)

shares rose 8% after the company announced an expansion of its drug discovery alliance with

Genentech

( DNA). As part of the expanded agreement, which calls for advanced research, development and commercialization of new biologic drugs, Lexicon will receive $25 million in payments and funding over the three-year advanced research portion of the deal. The company also will receive payments if certain drugs are approved and commercialized by Genentech. "The expansion of our alliance with Genentech reflects the success of our intial collaboration and is a validation of our gene knockout approach to defining gene function for drug discovery," Lexicon said in a statement. Shares were up 32 cents to $4.10.

Noven Pharmaceuticals

(NOVN) - Get Report

shed 19% after the Food and Drug Administration released a memo saying that the company's skin patch for treating attention deficit hyperactivity disorder in children can't be marketed safely. The patch, which being is co-developed by

Shire Pharmaceuticals

, is set to be reviewed by an FDA advisory panel Friday. According to the memo, the clinical reviewer for the product said the patch can't be marketed because of safety concerns, including insomnia, anorexia and weight loss. Noven shares recently had tumbled $2.54 to $10.97.

Amsurg

(AMSG)

fell 8% after Deutsche Bank reduced its rating on the operator of surgery centers to sell from hold. The broker also cut its price target to $21 from $23. Analyst Darren Lehrich said Amsurg's declining growth rate is cause for concern, and added that Amsurg's ability to return to mid-to-high-teen earnings growth may be "quite limited" during the next several years. Specifically, the firm said that it is concerned with Amsurg's decelerating same-store revenue growth, a deteriorating acquisition and development pipeline, and uncertainty surrounding potential Medicare payment reform. Shares of Amsurg recently traded down $1.81 to $22.30.

St. Jude Medical

(STJ)

agreed Thursday to acquire privately held Savacor for $50 million. The acquisition of Savacor, which makes heart failure diagnostic and therapy guidance products, is expected to close by the end of the year. St. Jude plans to record $50 million charge for related in-process research and development. "The Savacor technology has exciting potential and will complement the development efforts already underway at St. Jude Medical in managing the co-morbidities of heart failure patients," St. Jude said. The medical device maker's shares were up $1.38, or 3%, to $49.15.

Other health care volume movers included

Pfizer

(PFE) - Get Report

, up 13 cents to $21.33;

Wyeth

( WYE), down 35 cents to $41.21;

BioCryst Pharmaceuticals

(BCRX) - Get Report

, down $1.32 to $14.92;

SFBC International

( SFCC), down $4.59 to $16.50;

Bristol-Myers Squibb

(BMY) - Get Report

, up 6 cents to $21.65;

Merck

(MRK) - Get Report

, up 13 cents $29.53;

Novavax

(NVAX) - Get Report

, up 18 cents to $3.65;

Johnson & Johnson

(JNJ) - Get Report

, up 10 cents to $61.85;

Amgen

(AMGN) - Get Report

, up 82 cents to $81.75;

Schering-Plough

( SGP), down 42 cents to $18.90;

Gilead Sciences

(GILD) - Get Report

, up $2.41 to $53.10.