Zanamivir for the treatment of influenza A and B infection in high-risk patients - A pooled analysis of randomized controlled trials

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. Conclusions: 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.