Randomised trial of efficacy and safety of inhaled zanamivir in treatment of influenza A and B virus infections

Background Influenza affects many people worldwide each year and has many troublesome symptoms. We investigated the efficacy and safety of the inhaled antiviral agent zanamivir as a treatment for influenza A and B infection. Methods In a randomised, double-blind, placebo-controlled trial, we recruited 455 patients aged 12 years and older with influenza-like symptoms of 36 h duration or less who lived in Australia, New Zealand, and South Africa. Eligible patients were randomly assigned 10 mg inhaled zanamivir (n=227) or placebo (n=228) twice daily for 5 days. All patients recorded symptoms on diary cards four times daily during treatment and twice daily for 9 days after treatment. We analysed all patients by intention to treat, influenza positivity, and high risk of developing complications. Findings Compared with placebo, zanamavir relieved influenza symptoms a median of 1-5 days earlier in the intention-to-treat population (p=0-011), in influenza-positive patients (p=0-004), and in patients who were febrile at entry (p<0-001). In high-risk patients treated with zanamivir, symptoms were alleviated a median of 2-5 days earlier (p=0-048), fewer had complications (p=0-004), and fewer used complication-associated antibiotics (p=0-025) compared with placebo. The adverse event profiles were similar for zanamivir and placebo. Interpretation Zanamivir was well-tolerated and effective in shortening the duration and severity of influenza symptoms and, in high-risk patients, the rate of complications. Our findings need to be confirmed in future studies because of the small number of patients.