Safety Study to Assess IV Zanamivir for Treatment of Influenza Infection in Patients Who Are in Hospital

This study will be an open-label, Phase II, multi-center, single arm study to evaluate the safety and tolerability of IV zanamivir 600mg twice daily for 5 days in hospitalized subjects with laboratory confirmed influenza infection. The initial 5-day treatment course may be extended for up to 5 additional days if viral shedding is determined to be ongoing or if clinical symptoms warrant further treatment with IV zanamivir. Approximately 200 subjects will be enrolled into the study (approximately 150 adult/adolescent subjects and approximately 50 pediatric subjects). Adult (\>/= 18 years of age) with normal renal function will receive 600mg per dose. Pediatric (6 months to \<13 years)/adolescent (\>13 years to \<18 years) subjects will receive an age-adjusted, weight-based dose (not to exceed the 600 mg adult dose) intended to provide comparable systemic exposures to 600mg in adults. Subjects with renal impairment will receive an adjusted dose based on calculated creatinine clearance and renal replacement modality. Serum pharmacokinetic assessments will be performed in subjects across all age groups wherever possible. Pharmacokinetic analyses will be conducted, in real-time to the extent possible, when 4 subjects (from whom samples can be obtained) are enrolled in each of the following age cohorts: 6 months to less than 1 year; 1 to less than 2 years, and 2 to less than 6 years to determine the need for pediatric dose adjustments. PK assessments are required in the first 4 subjects enrolled in the 6 months to less than 1 year age cohort, and PK data must be analyzed and IV zanamivir dosage must be reviewed before additional subjects in this age cohort can be enrolled. The study duration is approximately 28 days for subjects whose treatment duration is 5 days, and up to approximately 33 days for subjects whose treatment duration is extended to a maximum of 10 days. The study will consist of Pre-dose Baseline Assessments (Day 1), During Treatment Assessments (Days 1 to 5, and up to Day 10), and Follow-up Assessments on the following days: Post-Treatment +2 +5, +9, +16 and +23 Days. If the first dose of IV zanamivir is administered in the afternoon/evening of Day 1, the twice daily dosing schedule will result in one treatment day encompassing two calendar days. For subjects who have been discharged from hospital, the Post-Treatment +2, +5, +9 and +16 Days Assessments can be made by telephone contact.