Two days after the government approved the purchase of NIS 150 million worth of Tamiflu to treat victims of avian flu, the British journal Nature reported on a way to cut dosage of the precious drug in half: It should be given along with a specific generic drug that stops Tamiflu from being excreted in the urine. The "helper" drug, called probenecid, stops many drugs - including antibiotics - from being removed from the blood by the kidneys. The technique was invented during World War II, but probenecid is still widely used alongside antibiotics in emergency rooms and in treating the sexually transmitted diseases gonorrhea and syphilis. The prospect of using the drug to stretch supplies of Tamiflu (oseltamivir phosphate) - which is in very short supply around the world - was raised last week by an unnamed emergency medicine specialist who was browsing safety data published by Tamiflu's Swiss manufacturer. He noticed that giving the flu drug with probenecid doubles the number of hours its active ingredient stays in the blood and doubles its maximum concentration in the blood. In other words, half a dose of Tamiflu with probenecid has the same effect as a dose without. "It dawned on me that the data potentially represented a tremendous therapeutic benefit," the specialist said Tuesday. Doctors have welcomed the idea, telling Nature that the combination therapy raised few safety considerations because probenecid was already so widely used. But some cautioned that, although using probenecid would make Tamiflu go further in emergency situations, coping with a large-scale pandemic still required a huge increase in the production of flu drugs. The World Health Organization and the US Food and Drug Administration declined to comment on the idea, an apparent lack of interest that scientists have described as "stupefying." The possibility of effectively doubling Tamiflu stocks comes just as US President George Bush is preparing to announce the US pandemic plan at the National Institutes of Health.