&NA;Oseltamivir (EN241104, RO640796, GS 4104, Tamiflu) is the lead compound from a group of carbocyclic compounds developed by Gilead Sciences and the University of California, Berkeley in collaboration with The Australian National University, Canberra. Oseltamivir is the ethyl ester prodrug of GS 4071, a potent and selective inhibitor of the influenza neuraminidase enzyme with low (< 5%) oral bioavailability. Oseltamivir has lipophilic properties and exhibits rapid enzymatic conversion to GS 4071.Roche has submitted an NDA with the FDA in the US, where oseltamivir will be marketed as Tamiflu. The company anticipates the application will receive a 6-month priority review. Regulatory filings have also been submitted in the European Union, Canada, and Switzerland. Oseltamivir is undergoing phase III clinical studies involving a variety of patients, including senior citizens, adults at risk of developing complications from the flu, healthy children as young as 1 year and children with asthma, in Australia, New Zealand, Hong Kong, South Africa and South America. Pivotal studies were initiated in Japan in the first quarter of 1999.Gilead has entered into an agreement with Roche for the development and marketing of influenza therapies. Under this agreement, Roche gained exclusive worldwide rights to Gilead's neuraminidase inhibitors, of which oseltamivir is the lead candidate. Roche is to pay Gilead $US10 million up front and a further $US40 million in milestone payments for worldwide marketing rights. In addition, Roche will fund all research and development costs and pay Gilead royalties on sales of marketed compounds.Oseltamivir has potent, broad spectrum activity against multiple strains of influenza A and B viruses, verified by clinical studies. Oseltamivir has demonstrated effectiveness in both the treatment and prevention of naturally occurring infections and compared with zanamivir, oseltamivir has the advantage of being administered orally. Oseltamivir could also potentially be a useful adjunct to the flu vaccine.