WASHINGTON (AP) — GlaxoSmithKline has notified doctors of at least one death caused by a inappropriate use of its anti-flu medication Relenza. In a letter sent Thursday to doctors, Glaxo said the death resulted after the drug was reformulated into a liquid form, something not recommended by the Food and Drug Administration. The agency posted the letter online Friday. It did not provide details on the person who died. Relenza comes in powder form for use with Glaxo's Diskhaler device. The drug is approved to treat symptoms of the seasonal flu when taken within two days of onset. FDA and London-based Glaxo stressed the safety of reconstituting Relenza has not been established. The U.S. has stockpiled millions of doses of Relenza and Roche's Tamiflu.