According to this week's "Nature", a physician has noticed that Tamiflu is actively excreted by the kidneys. Administering probenecid to stop this drug excretion (a technique already used with penicillin) increases the drug's effectiveness twofold and means that half the dose can be used. Roche has data on this from 2002 but has done nothing with it. Draw your own conclusions.
Nature, volume 438 (3 november 2005), News, page 6.