Zanamivir for the Treatment of Influenza A and B Infection in High-Risk Patients

Background: Influenza can cause significant morbidity and mortality, particularly in patients considered to be at high risk (such as the elderly and those with chronic disease) of developing influenza-related complications.Data on the efficacy of zanamivir in high-risk patients are lacking because individual studies recruited a limited number of these patients. Methods:A retrospective pooled analysis of data from high-risk patients in studies completed before or during the 1998-1999 winter season was performed to investigate the efficacy and safety of inhaled zanamivir (10 mg twice daily for 5 days) for the treatment of confirmed influenza.All studies were randomized, double-blind, and placebo-controlled with 21-to 28-day follow-up.A total of 2751 patients was recruited.Of these, 321 (12%) were considered high risk and 154 were randomized to zanamivir.The median time to alleviation of influenza symptoms and time to return to normal activities were the main outcome measures.Results: Zanamivir-treated high-risk patients had a treatment benefit of 2.5 days compared with those given placebo (P=.015).Patients treated with zanamivir returned to normal activities 3.0 days earlier (P=.022) and had an 11% reduction (P=.039) in the median total symptom score over 1 to 5 days relative to those taking placebo.In addition, zanamivir reduced the incidence of complications requiring antibiotic use by 43% relative to placebo users (P=.045).Adverse events reported were of a similar nature and frequency between the two groups. Conclusion:This pooled analysis shows that zanamivir is an effective and well-tolerated treatment for influenza in patients considered at high-risk of developing influenza-related complications.