Updated from 2:59 p.m. EDT

Shares of

Possis Medical

(POSS)

were among the worst-performing health and pharmaceutical stocks Tuesday after the company's treatment for blood clots in coronary arteries

failed to show clinical superiority over conventional treatment.

The company's catheter device, which has already been approved by the Food and Drug Administration for removing thrombus in native arteries and in saphenous vein bypass grafts, showed disappointing results in the company's postmarketing study. In the heart study, Possis measured the AngioJet XMI's effectiveness by studying the final infarct size on the heart within a month of heart surgery. The company concluded that the device "did not provide a basis for concluding that the AngioJet device should be routinely used for all heart attack patients to reduce final infarct size."

As a result of the weak study results, Possis said that it now expects to post 2005 earnings of 70 cents to 82 cents a share on sales of $85 million to $90 million, down from previous earnings guidance of 83 cents to 96 cents a share on sales of $92 million to $98 million. Analysts surveyed by Thomson First Call were expecting 2005 earnings of 87 cents on sales of $93.4 million. Shares traded down $12.23, or 39.8%, to $18.53.

BioCryst

(BCRX) - Get Report

traded actively after the FDA granted its lead anticancer drug orphan status for two additional indications. The orphan status designation allows BioCryst to receive prefiling regulatory guidance and reduced fees, and provides market exclusivity for seven years once the FDA approves the drug. After rising in early-morning action, shares of BioCryst traded down 17 cents, or 2.8%, to $5.87.

Shares of

AVI Biopharma

(AVII)

rose after the company announced a collaboration with the Centers for Disease Control and Prevention. The two-year agreement provides for further testing on AVI's Neugene antisense therapeutics, which is used for killing all four serotypes of dengue virus. It's estimated that 50 million to 100 million cases of dengue fever occur each year. High fever, severe frontal headache, joint and muscle pain, nausea, vomiting and a rash characterize dengue fever. Shares of AVI Biopharma traded up 26 cents, or 12.2%, to $2.39.

Seattle Genetics

(SGEN) - Get Report

rose after its myeloma therapy received orphan drug status. SGN-40, which is a humanized monoclonal antibody, is currently being evaluated by Seattle Genetics in a phase I study. In the event of FDA market approval, Seattle Genetics will be able to market SGN-40 exclusively for seven years. Previously, the company's SGN-30 drug received orphan status for Hodgkin's disease and T-cell lymphomas. Shares traded up 3 cents, or 0.4%, to $6.83.

Other health care volume movers included

Pfizer

(PFE) - Get Report

, down 12 cents to $31.53;

Sepracor

(SEPR)

, up $1.70 to $49.35;

Amgen

(AMGN) - Get Report

, up 78 cents to $58.83;

Boston Scientific

(BSX) - Get Report

, up 58 cents to $35.78;

Schering-Plough

(SGP)

, up 8 cents to $18.78; and

Johnson & Johnson

(JNJ) - Get Report

, up 12 cents to $57.17.