Shares of Myogen ( MYOG) were among the best-performing health-related stocks Monday, climbing 40% after the drug developer's treatment for pulmonary arterial hypertension performed well in a Phase III trial.

The company's ambrisentan drug met the primary endpoint of improved exercise capacity and its secondary endpoint of time to clinical worsening. "We believe the robustness of these results is unprecedented for oral therapies for patients with pulmonary arterial hypertension and represents a significant achievement for ambrisentan and Myogen," the company said.

Myogen also said ambrisentan was well tolerated in the study. The most frequent adverse event was headache, it said, which occurred in 12.7% of patients in the 5-milligram-dose group and 7.8% in the 2.5-milligram-dose group. Some 6.2% of those in the placebo group suffered from headaches. Shares of Myogen were trading up $7.77 to $27.04. Shares of Encysive Pharmaceuticals ( ENCY), which is developing its own pulmonary arterial hypertension drug, sank $3.64 to $7.54.

Pain Therapeutics ( PTIE) fell 9% after the drugmaker discontinued the development of its irritable bowel syndrome treatment. The company's PTI-901 drug candidate showed a favorable safety profile and patients had statistically meaningful relief of the syndrome during the second month of treatment, but the drug didn't show a meaningful benefit during the third month of treatment, the study's primary endpoint. Based on regulatory standards, an experimental drug for irritable bowel syndrome must show efficacy at the end of the three-month period.

As a result of the failed trial, Pain Therapeutics plans to discontinue all further clinical development activities of the drug. "This is an opportunity to sharpen our focus on our late-stage pipeline," the company said. "We're ready to start 2006 with a strong balance sheet, a modest cash burn rate and two lead drug candidates in Phase III clinical development." Shares were trading down 63 cents to $6.69.

Shares of Sierra Health Services ( SIE) rose 2% after the health-care services company affirmed its 2005 and 2006 earnings guidance. The company continues to expect 2005 earnings of $3.55 a share and 2006 earnings of $3.80 to $4 a share. Analysts polled by Thomson First Call project 2005 earnings of $3.51 a share and 2006 earnings of $4.03 a share. Sierra Health was up $1.33 to $81.16.

Cell Genesys ( CEGE) rose 3% after the company reported positive results from its Phase II trial of GVAX, a vaccine for chronic myelogenous leukemia. The initial findings of the trial showed that the vaccine reduced persistent leukemic disease in nine of 19 patients. The vaccine was administered to patients who continued to exhibit evidence of persistent leukemia despite being on Novartis' ( NVS - Get Report) Gleevec therapy for more than a year. Shares were up 17 cents to $5.69.

Shares of MedImmune ( MEDI) rose 4% after the company said its FluMist spray vaccine performed well vs. a flu shot in a head-to-head influenza study of children aged 6 months to 59 months. Preliminary data from a Phase III study showed that 8.6% of the study participants who received a flu shot got the flu, while only 3.9% got the flu after taking a new refrigerator-stable formulation of FluMist. "This pivotal trial is the third Phase III trial of CAIV-T to show statistically significant reductions in influenza compared to the injectible influenza vaccine," the company said.

FluMist is currently approved for children who are 5 to 17 years old, and adults who are 18 to 49. MedImmune plans to submit its data to the Food and Drug Administration during the second quarter of 2006. The company hopes to offer the updated FluMist product beginning in the 2007 flu season, if approved by the FDA. MedImmune shares were trading up $1.20 to $35.36.

Other health-care volume movers included Pfizer ( PFE - Get Report), down 29 cents to $20.31; Merck ( MRK), down $1.09 to $28.04; Teva Pharmaceutical Industries ( TEVA - Get Report), down 93 cents to $43.55; Elan ( ELN), down 28 cents to $12.66; Johnson & Johnson ( JNJ), up 10 cents to $60.20; Abbott Labs ( ABT), down 7 cents to $38.92; Bristol-Myers Squibb ( BMY), down 26 cents to $21.16; Guidant ( GDT), up 29 cents to $67.49; UnitedHealth Group ( UNH), down 96 cents to $62.71; and Schering-Plough ( SGP), down 13 cents to $19.33.