Due in part to widespread availability of oseltamivir and clinical experience using oseltamivir to treat H5N1 influenza virus infections, many strains of influenza have become resistant to it. Other reliable methods of treating H5N1 must be identified in case of a pandemic. One such option is intravenous zanamivir used in combination with oseltamivir. The primary purpose of this study is to evaluate the interaction between oral oseltamivir and intravenous zanamivir administered as either a continuous or intermittent infusion in healthy adults.