Crossover Study to Investigate the Safety, Tolerability, and Pharmacokinetics of Repeat Dose Zanamivir/Placebo Via Devices Administered Twice Daily for 5 Days

The purpose of this study is to compare the safety and tolerability of Zanamivir using a Rotahaler to placebo within the Rotahaler presentation and to the Diskhaler. Eighteen subjects will receive each of three treatments for 5 days in a 3-way crossover design.