Rapid antiviral effect of inhaled zanamivir in the treatment of naturally occurring influenza in otherwise healthy adults

The antiviral and clinical effects of inhaled zanamivir (10 mg twice daily for 5 days, started within the first or second day of a flulike illness) we re evaluated in a randomized, placebo-controlled trial during the 1997-1998 influenza season in Canada. Pharyngeal secretions were collected with swab s every 12 h during 6 days, and symptoms were self-evaluated twice daily du ring 14 days. After only 12 h of treatment (1 dose), median virus titers de creased by 1.0 log(10) TCID50/mL in the zanamivir group (n = 17), compared with a 0.42-log(10) increase in the placebo group (n = 10; P = .08). This w as associated with a 4.5-day (47.4%) reduction in the median time to allevi ation of all significant flu symptoms in the zanamivir recipients (P = .03 after adjusting for the initial virus titer and the time between onset of s ymptoms and treatment). Resistance to zanamivir was not detected in virus i solates by either phenotypic or genotypic assays.