Biota shares tumble on weak flu drug study SHARES in Biota slumped more than 10 per cent today after releasing weak preliminary results from a prophylaxis study for its flu drug Inavir. The influenza Phase III prophylaxis study, conducted during the 2009-2010 pandemic flu season in Japan, gave subjects one of two doses of CS-8958, or Inavir, to evaluate the prevention and safety of the drug in families of influenza A and B sufferers. Biota's Japanese partner Daiichi Sankyo last September received approval to manufacture and market Inavir, or laninamivir octanoate, in Japan. Daiichi has achieved "significant" sales since, with the prophylaxis study looking at prevention rather than treatment. But Biota today said the trial showed the protective efficacies of a single, inhaled dose of CS-8958 of 20mg and 40mg -- as measured by the risk reduction rate (RRR) -- were 43.7 per cent and 43.2 per cent respectively, lower than the preset RRR endpoint of 70 per cent. "The possible reasons offered for the lower protective efficacies were the low infection rate within families in the placebo group (8.6 per cent) and the growth in public awareness, resulting in the use of other preventative infection measures during the 09H1N1 (swine flu) pandemic," the company said. Biota will continue to update shareholders when additional trials commence. By late morning, shares in Biota were down 10 cents, or 9.8 per cent at 92 cents, slashing its market value to $168 million from $185m. The stock fell as low as 91 cents at one stage in the morning, a slide of 10.8 per cent. Inavir is a new class of long acting neuraminidase inhibitors (LANIs) delivered by inhaler designed to address the limitation of influenza anti-virals, which require daily or more frequent dosing. Inavir is Daiichi's registered brand and one of a range of second generation influenza antivirals co-owned by Melbourne-based Biota and the Japanese firm.