Wood Mackenzie, an Edinburgh-based research and consulting firm, reviews recent trends in biotechnology stocks. The Nasdaq biotechnology index rose in February and dropped back in March, but the overall trend remains positive, with a gain of 6% since the start of the year. February saw strong 2005 financial results posted by many of the major biotech companies, bolstering investor confidence in the sector.

The changing fortunes of Biogen Idec in Cambridge, Massachusetts, had a particularly strong influence on the index. The company's year so far has been a tale of two antibodies. Its shares rose 12% in February when the US Food and Drug Administration (FDA) approved its anticancer antibody Rituxan to treat rheumatoid arthritis and an FDA advisory committee recommended that the antibody Tysabri should return to market to treat multiple sclerosis. Tysabri had been withdrawn from sale in February 2005 on safety grounds. The FDA subsequently delayed making a final decision on the drug, causing Biogen's shares to shed much of their earlier advance.

Other share movements were dictated by the results of clinical trials. Adolor of Exton, Pennsylvania, saw its share value rise by more than half after good trial results for its post-surgery bowel treatment Entereg. Another Pennsylvania company, Novavax in Malvern, enjoyed a whopping 79% increase in its share price after presenting promising preclinical data on its early-stage bird-flu vaccine.

But Antigenics of New York lost almost half its share value when experimental cancer drug Oncophage failed to meet expectations in kidney cancer patients. And unexpected side effects from hepatitis C treatment valopicitabine shaved nearly 40% from the share price of Idenix Pharmaceuticals of Cambridge, Massachusetts.