Updated from 3:45 p.m. Shares of Vivus ( VVUS) were among the best-performing health-related stocks Thursday, rising 18.3% after the company announced positive results from its phase II study of Avanafil, the company's experimental impotence drug. The drug, which was well tolerated and showed no serious adverse events, did particularly well at the 300-milligram level. "The ability to initiate intercourse in 30 minutes, which is half the time as compared to the recommended initiation time of two of the currently approved PDE5 inhibitors, while maintaining a high degree of efficacy, should help differentiate Avanafil and give men a meaningful option to treat their ED," one of the investigators in the study said. The study covered 284 patients who were treated with placebo or Avanfil at various doses for 12 weeks. Shares traded up 61 cents to $3.95. Applied Biosystems ( ABI) fell 1.5% after the company said it would cut about 250 jobs in its research and development, marketing and operations areas. Applied expects to take a pretax charge during the fourth quarter of between $20 million and $22 million, which will cover severance costs and the closing of facilities. "These adjustments are in keeping with our program to enhance Applied Biosystems' performance and should better align our resources with the needs of our customers," the company said. During fiscal 2006, the company expects to add employees in field sales and support, manufacturing quality and advanced research, it said. Shares traded down 32 cents to $20.49. Shares of McKesson ( MCK) fell modestly after the company announced a contract extension with the U.K.'s National Health Service. The contract extension, which brings the contract term to 12.75 years, up from 10 years, calls for McKesson to continue providing an electronic staff record system for managing human resources and payroll. McKesson will receive a cash payment of $143 million as part of the new extension, mostly for McKesson's investment in the project to date. Shares traded down 12 cents to $43.47.