Shares of

Inhibitex

( INHX) were among the worst-performing health-related stocks Monday, plunging 61% after the biotechnology company said its Veronate drug failed to meet its primary endpoint in a phase III study.

The drug, used to prevent hospital-associated infections in premature infants, failed to lower the staph infection rate of premature babies weighing 500 grams to 1,250 grams at birth. The company said there were no measurable trends in favor of Veronate for the primary or any of the secondary endpoints. "The outcome of the trial was unexpected against the background of our preclinical studies and favorable phase II trends such that additional scrutiny is warranted," the company said. Shares were trading down $4.42 to $2.84, hitting a 52-week low.

Sirna Therapeutics

( RNAI) jumped 14% after the company announced a drug development agreement with

GlaxoSmithKline

(GSK) - Get Report

. As part of the agreement, GlaxoSmithKline will make an upfront payment of $12 million to Sirna, which will consist of cash and a stock purchase priced at $8.36 a share. In all, Sirna could receive more than $700 million in milestone payments during the multiyear alliance. Shares were trading up 98 cents to $7.72.

Shares of

Cortex Pharmaceuticals

(COR) - Get Report

tumbled 51% after the Food and Drug Administration halted trials of the company's Ampakine CX717 technology, which is being developed to treat the neurodegenerative effects of aging and disease. "The action taken by the FDA is related to concerns over some preclinical animal data and not to results from any human clinical trials," the company said. Cortex, which received a phone call from the FDA on Friday afternoon, expects to receive formal written notice about the halted trials within the next seven to 10 days. "After Cortex receives the written notification from the FDA, has had a chance to analyze its contents, and has had discussions with the appropriate personnel within the agency, it plans to provide an update for shareholders and investors on this issue," the company said. Shares fell $2.68 to $2.57.

Incyte

(INCY) - Get Report

slid 34% after the drug developer discontinued the development of DFC as an HIV treatment. As a result, the company also cut its financial assumptions for cash use during the year. Incyte said the trial was halted because of an observed increase in the frequency of grade 4 hyperlipasemia, a sign of pancreatic inflammation. "This is an unfortunate and disappointing finding as we have seen clinically meaningful antiviral effects in patients taking the 200 mg dose of DFC without 3TC or FTC," the company said. "Even though lower doses could be safer, those we've studied have not been effective and we believe it is in the best interest of patients to discontinue DFC's development."

Looking ahead, Incyte now sees cash use of $88 million to $95 million during 2006, down from an earlier estimate of $98 million to $105 million. The company lowered its research and development expense projection to a range of $82 million to $88 million from an earlier forecast of $92 million to $98 million. Shares were down $2.12 to $3.90.

Shares of

Medarex

( MEDX) fell 3% after the biopharmaceutical company said that it plans to sell 10 million shares of stock. Proceeds from the offering, which is being underwritten by J.P. Morgan Securities and Goldman Sachs, will be used to fund the company's research programs and product development, as well as other general needs. Shares were trading down 35 cents to $12.87.

Other health care volume movers included

Generex Biotechnology

(GNBT)

, down 27 cents to $2.80;

Pfizer

(PFE) - Get Report

, up 20 cents to $25.12;

StemCells

(STEM)

, down 42 cents to $3.16;

Boston Scientific

(BSX) - Get Report

, down 18 cents to $22.87;

UnitedHealth Group

(UNH) - Get Report

, up 20 cents to $56.06;

Johnson & Johnson

(JNJ) - Get Report

, up 6 cents to $59.28;

Amgen

(AMGN) - Get Report

, down 51 cents to $72.24;

Bristol-Myers Squibb

(BMY) - Get Report

, up 22 cents to $24.83;

Elan

(ELN)

, up 12 cents to $14.56;

Merck

(MRK) - Get Report

, up 25 cents to $35.48; and

Schering-Plough

( SGP), up 2 cents to $19.01.